Chapter 5 The Working Cell © 2016 Pearson Education, Inc.

Chapter 5: Concepts Energy : Kinetic, Potential, chemical and Entropy
ATP: How we get energy out of it Enzymes: Activation energy, importance of shape Membrane function: Active and Passive transport plus cell signaling Osmosis Exocytosis and Endocytosis

Why Cellular Functions Matter
Figure 5.0-1 Figure Why cellular functions matter

Biology and Society: Harnessing Cellular Structures
You can think of a cell as a machine that continuously and efficiently performs a variety of functions, such as movement, energy processing, and production of various products. © 2016 Pearson Education, Inc. 4

Chapter Thread: Nanotechnology
Figure 5.0-2 Figure Nanotechnology: cellular structures

Like other cells, a sperm cell generates energy by breaking down sugars and other molecules that pass through its plasma membrane. Enzymes within the cell carry out a process called glycolysis. During glycolysis, the energy released from the breakdown of glucose is used to produce molecules of ATP. Within a living sperm, the ATP produced during glycolysis and other processes provides the energy that propels the sperm through the female reproductive tract. © 2016 Pearson Education, Inc. 6

To harness this energy-producing system, researchers attached three glycolysis enzymes to a computer chip. The enzymes continued to function in this artificial system, producing energy from sugar. The hope is that a larger set of enzymes can eventually be used to power microscopic robots. © 2016 Pearson Education, Inc. 7

Some Basic Energy Concepts
Energy makes the world go round . All organisms require energy to stay alive But what is energy? Energy is defined as the capacity to perform work. Some forms of energy are used to perform work, such as moving an object against an opposing force. Energy is the ability to rearrange a collection of matter. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students with limited exposure to physics may have never understood the concepts of “energy” and “the conservation of energy” or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. 2. Although typically familiar with the concept of dietary Calories, students often struggle to think of Calories as a source of potential energy. For many students, it is not immediately clear how energy is stored in food. Teaching Tips 1. Some students can relate well to the concept of entropy as it relates to the room where they live. Despite cleaning up and organizing the room on a regular (or irregular) basis, the room increasingly becomes disorganized, a victim of entropy, until another energy input (or effort) is exerted to make the room more orderly again. Students might even get to know “entropy” as the “dorm room effect.” 2. All too often we hear or read that some thing or reaction creates energy. We might hear or read that a power plant “produces” energy or that mitochondria “make” energy. Even in our classroom conversations, we may occasionally slip into this error. When discussing the first law of thermodynamics, consider emphasizing the inaccuracy of such statements. 3. The heat produced by the engine of a car is typically used to heat the car during cold weather. But is this same heat available in warmer weather? Students are often unaware that their car “heater” works very well in the summer, too. Just as exercise can warm us when it is cold, the same extra heat is released when we exercise in warm conditions. A car engine in the summer struggles to dissipate heat in the same way that a human struggles to cool off after exercising when the weather is warm. 4. Here is a calculation that has impressed some students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0° to 100°C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-L bottles you can help students visualize how much liquid water can be raised from 0° to 100°C. (Note: 200 Calories raises about 2 L of water 100°C; but it takes much more energy to melt ice or to convert boiling water into steam.) 5. The same mass of fat (about 9 kcal per gram) stores nearly twice as many Calories as an equivalent mass of protein or carbohydrates (about 4.5–5 kcal per gram). Thus, when comparing equal masses of fat, protein, and lipid, the fat has nearly twice the potential energy. Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 pounds overweight, you would be nearly 40 pounds overweight if the same energy were stored as carbohydrates or proteins instead of fat.) Active Lecture Tips 1. Challenge your students to come up with examples of common energy conversions in their lives. Have students turn to someone seated near them to find at least two examples. In our daily lives, we rely upon many energy transformations. On our classroom walls, a clock converts electrical energy to mechanical energy to sweep the hands around the clock’s face (unless it is digital!). Our physical (mechanical) activities walking to and from the classroom rely upon the chemical energy from our diet. This chemical energy in our diet also helps us maintain a steady body temperature (heat). 2. Challenge your students to explain why they feel warm when it is 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). Shouldn’t they feel cold? Have students work in groups of two or three to think this through. The answer is that our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a core body temperature around 37°C. Thus, we sweat and behave in ways that help release our extra heat generated in cellular respiration. 3. See the Activity Keeping an Organized Dorm Room Requires Energy, Just Like in a Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 9

Conservation of Energy
Energy primarily come into two different types Kinetic energy is the energy of motion. Potential energy is stored energy, energy that an object has because of its location or structure. Life depends on countless similar conversions of energy from one form to another. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students with limited exposure to physics may have never understood the concepts of “energy” and “the conservation of energy” or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. 2. Although typically familiar with the concept of dietary Calories, students often struggle to think of Calories as a source of potential energy. For many students, it is not immediately clear how energy is stored in food. Teaching Tips 1. Some students can relate well to the concept of entropy as it relates to the room where they live. Despite cleaning up and organizing the room on a regular (or irregular) basis, the room increasingly becomes disorganized, a victim of entropy, until another energy input (or effort) is exerted to make the room more orderly again. Students might even get to know “entropy” as the “dorm room effect.” 2. All too often we hear or read that some thing or reaction creates energy. We might hear or read that a power plant “produces” energy or that mitochondria “make” energy. Even in our classroom conversations, we may occasionally slip into this error. When discussing the first law of thermodynamics, consider emphasizing the inaccuracy of such statements. 3. The heat produced by the engine of a car is typically used to heat the car during cold weather. But is this same heat available in warmer weather? Students are often unaware that their car “heater” works very well in the summer, too. Just as exercise can warm us when it is cold, the same extra heat is released when we exercise in warm conditions. A car engine in the summer struggles to dissipate heat in the same way that a human struggles to cool off after exercising when the weather is warm. 4. Here is a calculation that has impressed some students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0° to 100°C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-L bottles you can help students visualize how much liquid water can be raised from 0° to 100°C. (Note: 200 Calories raises about 2 L of water 100°C; but it takes much more energy to melt ice or to convert boiling water into steam.) 5. The same mass of fat (about 9 kcal per gram) stores nearly twice as many Calories as an equivalent mass of protein or carbohydrates (about 4.5–5 kcal per gram). Thus, when comparing equal masses of fat, protein, and lipid, the fat has nearly twice the potential energy. Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 pounds overweight, you would be nearly 40 pounds overweight if the same energy were stored as carbohydrates or proteins instead of fat.) Active Lecture Tips 1. Challenge your students to come up with examples of common energy conversions in their lives. Have students turn to someone seated near them to find at least two examples. In our daily lives, we rely upon many energy transformations. On our classroom walls, a clock converts electrical energy to mechanical energy to sweep the hands around the clock’s face (unless it is digital!). Our physical (mechanical) activities walking to and from the classroom rely upon the chemical energy from our diet. This chemical energy in our diet also helps us maintain a steady body temperature (heat). 2. Challenge your students to explain why they feel warm when it is 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). Shouldn’t they feel cold? Have students work in groups of two or three to think this through. The answer is that our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a core body temperature around 37°C. Thus, we sweat and behave in ways that help release our extra heat generated in cellular respiration. 3. See the Activity Keeping an Organized Dorm Room Requires Energy, Just Like in a Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 10

Animation: Energy Concepts
© 2016 Pearson Education, Inc.

Greatest potential energy Climbing converts kinetic energy to
Figure 5.1 Greatest potential energy Climbing converts kinetic energy to potential energy. Diving converts potential energy to kinetic energy. Least potential energy Figure 5.1 Energy conversions during a dive

Conservation of Energy
A physical principle known as conservation of energy explains that it is not possible to destroy or create energy. Energy can only be converted from one form to another. The molecules of food, gasoline, and other fuels have a form of potential energy called chemical energy, which arises from the arrangement of atoms and can be released by a chemical reaction. For example, the chemical energy in the covalent bonds of gasoline molecules is converted to kinetic energy to move the car © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students with limited exposure to physics may have never understood the concepts of “energy” and “the conservation of energy” or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. 2. Although typically familiar with the concept of dietary Calories, students often struggle to think of Calories as a source of potential energy. For many students, it is not immediately clear how energy is stored in food. Teaching Tips 1. Some students can relate well to the concept of entropy as it relates to the room where they live. Despite cleaning up and organizing the room on a regular (or irregular) basis, the room increasingly becomes disorganized, a victim of entropy, until another energy input (or effort) is exerted to make the room more orderly again. Students might even get to know “entropy” as the “dorm room effect.” 2. All too often we hear or read that some thing or reaction creates energy. We might hear or read that a power plant “produces” energy or that mitochondria “make” energy. Even in our classroom conversations, we may occasionally slip into this error. When discussing the first law of thermodynamics, consider emphasizing the inaccuracy of such statements. 3. The heat produced by the engine of a car is typically used to heat the car during cold weather. But is this same heat available in warmer weather? Students are often unaware that their car “heater” works very well in the summer, too. Just as exercise can warm us when it is cold, the same extra heat is released when we exercise in warm conditions. A car engine in the summer struggles to dissipate heat in the same way that a human struggles to cool off after exercising when the weather is warm. 4. Here is a calculation that has impressed some students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0° to 100°C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-L bottles you can help students visualize how much liquid water can be raised from 0° to 100°C. (Note: 200 Calories raises about 2 L of water 100°C; but it takes much more energy to melt ice or to convert boiling water into steam.) 5. The same mass of fat (about 9 kcal per gram) stores nearly twice as many Calories as an equivalent mass of protein or carbohydrates (about 4.5–5 kcal per gram). Thus, when comparing equal masses of fat, protein, and lipid, the fat has nearly twice the potential energy. Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 pounds overweight, you would be nearly 40 pounds overweight if the same energy were stored as carbohydrates or proteins instead of fat.) Active Lecture Tips 1. Challenge your students to come up with examples of common energy conversions in their lives. Have students turn to someone seated near them to find at least two examples. In our daily lives, we rely upon many energy transformations. On our classroom walls, a clock converts electrical energy to mechanical energy to sweep the hands around the clock’s face (unless it is digital!). Our physical (mechanical) activities walking to and from the classroom rely upon the chemical energy from our diet. This chemical energy in our diet also helps us maintain a steady body temperature (heat). 2. Challenge your students to explain why they feel warm when it is 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). Shouldn’t they feel cold? Have students work in groups of two or three to think this through. The answer is that our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a core body temperature around 37°C. Thus, we sweat and behave in ways that help release our extra heat generated in cellular respiration. 3. See the Activity Keeping an Organized Dorm Room Requires Energy, Just Like in a Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 13

Heat Every energy conversion releases some randomized energy in the form of heat Heat is a type of kinetic energy contained in the random motion of atoms and molecules. a product of all energy conversions © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students with limited exposure to physics may have never understood the concepts of “energy” and “the conservation of energy” or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. 2. Although typically familiar with the concept of dietary Calories, students often struggle to think of Calories as a source of potential energy. For many students, it is not immediately clear how energy is stored in food. Teaching Tips 1. Some students can relate well to the concept of entropy as it relates to the room where they live. Despite cleaning up and organizing the room on a regular (or irregular) basis, the room increasingly becomes disorganized, a victim of entropy, until another energy input (or effort) is exerted to make the room more orderly again. Students might even get to know “entropy” as the “dorm room effect.” 2. All too often we hear or read that some thing or reaction creates energy. We might hear or read that a power plant “produces” energy or that mitochondria “make” energy. Even in our classroom conversations, we may occasionally slip into this error. When discussing the first law of thermodynamics, consider emphasizing the inaccuracy of such statements. 3. The heat produced by the engine of a car is typically used to heat the car during cold weather. But is this same heat available in warmer weather? Students are often unaware that their car “heater” works very well in the summer, too. Just as exercise can warm us when it is cold, the same extra heat is released when we exercise in warm conditions. A car engine in the summer struggles to dissipate heat in the same way that a human struggles to cool off after exercising when the weather is warm. 4. Here is a calculation that has impressed some students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0° to 100°C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-L bottles you can help students visualize how much liquid water can be raised from 0° to 100°C. (Note: 200 Calories raises about 2 L of water 100°C; but it takes much more energy to melt ice or to convert boiling water into steam.) 5. The same mass of fat (about 9 kcal per gram) stores nearly twice as many Calories as an equivalent mass of protein or carbohydrates (about 4.5–5 kcal per gram). Thus, when comparing equal masses of fat, protein, and lipid, the fat has nearly twice the potential energy. Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 pounds overweight, you would be nearly 40 pounds overweight if the same energy were stored as carbohydrates or proteins instead of fat.) Active Lecture Tips 1. Challenge your students to come up with examples of common energy conversions in their lives. Have students turn to someone seated near them to find at least two examples. In our daily lives, we rely upon many energy transformations. On our classroom walls, a clock converts electrical energy to mechanical energy to sweep the hands around the clock’s face (unless it is digital!). Our physical (mechanical) activities walking to and from the classroom rely upon the chemical energy from our diet. This chemical energy in our diet also helps us maintain a steady body temperature (heat). 2. Challenge your students to explain why they feel warm when it is 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). Shouldn’t they feel cold? Have students work in groups of two or three to think this through. The answer is that our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a core body temperature around 37°C. Thus, we sweat and behave in ways that help release our extra heat generated in cellular respiration. 3. See the Activity Keeping an Organized Dorm Room Requires Energy, Just Like in a Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 14

Entropy This is the second law of Thermodynamic
Scientists use the term entropy as a measure of disorder, or randomness in a system. All energy conversions increase the entropy of the universe This is because some energy is always “lost” as heat No energy conversion is ever perfectly 100% efficient Example: food web trophic levels This is the second law of Thermodynamic If energy is not destroyed where it has gone when the diver hits the water? It has been converted to heat in the air and then in water which is produced by the friction between the body and its surroundings.

Chemical Energy Living cells and automobile engines use the same basic process to make the chemical energy stored in their fuels available for work. In both cases, this process breaks organic fuel into smaller waste molecules that have much less chemical energy than the fuel molecules did, thereby releasing energy that can be used to perform work. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students with limited exposure to physics may have never understood the concepts of “energy” and “the conservation of energy” or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. 2. Although typically familiar with the concept of dietary Calories, students often struggle to think of Calories as a source of potential energy. For many students, it is not immediately clear how energy is stored in food. Teaching Tips 1. Some students can relate well to the concept of entropy as it relates to the room where they live. Despite cleaning up and organizing the room on a regular (or irregular) basis, the room increasingly becomes disorganized, a victim of entropy, until another energy input (or effort) is exerted to make the room more orderly again. Students might even get to know “entropy” as the “dorm room effect.” 2. All too often we hear or read that some thing or reaction creates energy. We might hear or read that a power plant “produces” energy or that mitochondria “make” energy. Even in our classroom conversations, we may occasionally slip into this error. When discussing the first law of thermodynamics, consider emphasizing the inaccuracy of such statements. 3. The heat produced by the engine of a car is typically used to heat the car during cold weather. But is this same heat available in warmer weather? Students are often unaware that their car “heater” works very well in the summer, too. Just as exercise can warm us when it is cold, the same extra heat is released when we exercise in warm conditions. A car engine in the summer struggles to dissipate heat in the same way that a human struggles to cool off after exercising when the weather is warm. 4. Here is a calculation that has impressed some students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0° to 100°C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-L bottles you can help students visualize how much liquid water can be raised from 0° to 100°C. (Note: 200 Calories raises about 2 L of water 100°C; but it takes much more energy to melt ice or to convert boiling water into steam.) 5. The same mass of fat (about 9 kcal per gram) stores nearly twice as many Calories as an equivalent mass of protein or carbohydrates (about 4.5–5 kcal per gram). Thus, when comparing equal masses of fat, protein, and lipid, the fat has nearly twice the potential energy. Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 pounds overweight, you would be nearly 40 pounds overweight if the same energy were stored as carbohydrates or proteins instead of fat.) Active Lecture Tips 1. Challenge your students to come up with examples of common energy conversions in their lives. Have students turn to someone seated near them to find at least two examples. In our daily lives, we rely upon many energy transformations. On our classroom walls, a clock converts electrical energy to mechanical energy to sweep the hands around the clock’s face (unless it is digital!). Our physical (mechanical) activities walking to and from the classroom rely upon the chemical energy from our diet. This chemical energy in our diet also helps us maintain a steady body temperature (heat). 2. Challenge your students to explain why they feel warm when it is 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). Shouldn’t they feel cold? Have students work in groups of two or three to think this through. The answer is that our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a core body temperature around 37°C. Thus, we sweat and behave in ways that help release our extra heat generated in cellular respiration. 3. See the Activity Keeping an Organized Dorm Room Requires Energy, Just Like in a Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 16

Energy conversions in a car and a cell
Fuel rich in chemical energy Energy conversion Waste products poor in chemical Gasoline  Oxygen Carbon dioxide Water Energy conversion in a car Energy for cellular work Energy conversion in a cell Heat Food Combustion Cellular respiration Kinetic energy of movement ATP Figure 5.2 Energy conversions in a car and a cell In both car and a cell, the chemical energy of organic fuel is harvested using oxygen. This chemical breakdown releases energy stored in the fuel molecules and produces CO2 and H2O. The released energy can be used to perform work.

Chemical Energy Cellular respiration is
the energy-releasing chemical breakdown of fuel molecules and the storage of that energy in a form the cell can use to perform work. Humans convert about 34% of our food energy to useful work such as the contraction of muscles. The rest of the energy released by the breakdown of fuel molecules generates body heat. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students with limited exposure to physics may have never understood the concepts of “energy” and “the conservation of energy” or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. 2. Although typically familiar with the concept of dietary Calories, students often struggle to think of Calories as a source of potential energy. For many students, it is not immediately clear how energy is stored in food. Teaching Tips 1. Some students can relate well to the concept of entropy as it relates to the room where they live. Despite cleaning up and organizing the room on a regular (or irregular) basis, the room increasingly becomes disorganized, a victim of entropy, until another energy input (or effort) is exerted to make the room more orderly again. Students might even get to know “entropy” as the “dorm room effect.” 2. All too often we hear or read that some thing or reaction creates energy. We might hear or read that a power plant “produces” energy or that mitochondria “make” energy. Even in our classroom conversations, we may occasionally slip into this error. When discussing the first law of thermodynamics, consider emphasizing the inaccuracy of such statements. 3. The heat produced by the engine of a car is typically used to heat the car during cold weather. But is this same heat available in warmer weather? Students are often unaware that their car “heater” works very well in the summer, too. Just as exercise can warm us when it is cold, the same extra heat is released when we exercise in warm conditions. A car engine in the summer struggles to dissipate heat in the same way that a human struggles to cool off after exercising when the weather is warm. 4. Here is a calculation that has impressed some students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0° to 100°C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-L bottles you can help students visualize how much liquid water can be raised from 0° to 100°C. (Note: 200 Calories raises about 2 L of water 100°C; but it takes much more energy to melt ice or to convert boiling water into steam.) 5. The same mass of fat (about 9 kcal per gram) stores nearly twice as many Calories as an equivalent mass of protein or carbohydrates (about 4.5–5 kcal per gram). Thus, when comparing equal masses of fat, protein, and lipid, the fat has nearly twice the potential energy. Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 pounds overweight, you would be nearly 40 pounds overweight if the same energy were stored as carbohydrates or proteins instead of fat.) Active Lecture Tips 1. Challenge your students to come up with examples of common energy conversions in their lives. Have students turn to someone seated near them to find at least two examples. In our daily lives, we rely upon many energy transformations. On our classroom walls, a clock converts electrical energy to mechanical energy to sweep the hands around the clock’s face (unless it is digital!). Our physical (mechanical) activities walking to and from the classroom rely upon the chemical energy from our diet. This chemical energy in our diet also helps us maintain a steady body temperature (heat). 2. Challenge your students to explain why they feel warm when it is 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). Shouldn’t they feel cold? Have students work in groups of two or three to think this through. The answer is that our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a core body temperature around 37°C. Thus, we sweat and behave in ways that help release our extra heat generated in cellular respiration. 3. See the Activity Keeping an Organized Dorm Room Requires Energy, Just Like in a Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 18

Food Calories A calorie (cal) is the amount of energy that can raise the temperature of 1 gram (g) of water by 1°C. Food Calories are kilocalories, equal to 1,000 calories. The energy of calories in food is is burned off by many activities activities . © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Students with limited exposure to physics may have never understood the concepts of “energy” and “the conservation of energy” or distinguished between potential and kinetic energy. Understanding such broad and new abstract concepts requires time and concrete examples. 2. Although typically familiar with the concept of dietary Calories, students often struggle to think of Calories as a source of potential energy. For many students, it is not immediately clear how energy is stored in food. Teaching Tips 1. Some students can relate well to the concept of entropy as it relates to the room where they live. Despite cleaning up and organizing the room on a regular (or irregular) basis, the room increasingly becomes disorganized, a victim of entropy, until another energy input (or effort) is exerted to make the room more orderly again. Students might even get to know “entropy” as the “dorm room effect.” 2. All too often we hear or read that some thing or reaction creates energy. We might hear or read that a power plant “produces” energy or that mitochondria “make” energy. Even in our classroom conversations, we may occasionally slip into this error. When discussing the first law of thermodynamics, consider emphasizing the inaccuracy of such statements. 3. The heat produced by the engine of a car is typically used to heat the car during cold weather. But is this same heat available in warmer weather? Students are often unaware that their car “heater” works very well in the summer, too. Just as exercise can warm us when it is cold, the same extra heat is released when we exercise in warm conditions. A car engine in the summer struggles to dissipate heat in the same way that a human struggles to cool off after exercising when the weather is warm. 4. Here is a calculation that has impressed some students. Depending on the size and activity of a person, a human might burn 2,000 dietary Calories (kilocalories) a day. This is enough energy to raise the temperature of 20 L of liquid water from 0° to 100°C. This is something to think about the next time you heat water on the stove! If you can bring in ten 2-L bottles you can help students visualize how much liquid water can be raised from 0° to 100°C. (Note: 200 Calories raises about 2 L of water 100°C; but it takes much more energy to melt ice or to convert boiling water into steam.) 5. The same mass of fat (about 9 kcal per gram) stores nearly twice as many Calories as an equivalent mass of protein or carbohydrates (about 4.5–5 kcal per gram). Thus, when comparing equal masses of fat, protein, and lipid, the fat has nearly twice the potential energy. Fat is therefore an efficient way to store energy in animals and many plants. To store an equivalent amount of energy in the form of carbohydrates or proteins would require about twice the mass, adding a significant burden to the organism’s structure. (For example, if you were 20 pounds overweight, you would be nearly 40 pounds overweight if the same energy were stored as carbohydrates or proteins instead of fat.) Active Lecture Tips 1. Challenge your students to come up with examples of common energy conversions in their lives. Have students turn to someone seated near them to find at least two examples. In our daily lives, we rely upon many energy transformations. On our classroom walls, a clock converts electrical energy to mechanical energy to sweep the hands around the clock’s face (unless it is digital!). Our physical (mechanical) activities walking to and from the classroom rely upon the chemical energy from our diet. This chemical energy in our diet also helps us maintain a steady body temperature (heat). 2. Challenge your students to explain why they feel warm when it is 30°C (86°F) outside if their core body temperature is 37°C (98.6°F). Shouldn’t they feel cold? Have students work in groups of two or three to think this through. The answer is that our bodies are always producing heat. At these higher temperatures, we are producing more heat than we need to maintain a core body temperature around 37°C. Thus, we sweat and behave in ways that help release our extra heat generated in cellular respiration. 3. See the Activity Keeping an Organized Dorm Room Requires Energy, Just Like in a Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 19

(kilocalories) we burn in various activities
Food Food Calories Activity Food Calories consumed per hour by a 150-pound person* Cheeseburger 295 Running (7 min/mi) 979 Spaghetti with sauce (1 cup) 241 Dancing (fast) 510 Baked potato (plain, with skin) 220 Bicycling (10 mph) 490 Fried chicken (drumstick) 193 Swimming (2 mph) 408 Bean burrito 189 Walking (3 mph) 245 Pizza with pepperoni (1 slice) 181 Dancing (slow) 204 Peanuts (1 ounce) 166 Playing the piano 73 Apple 81 Driving a car 61 Garden salad (2 cups) 56 Sitting (writing) 28 Popcorn (plain, 1 cup) 31 *Not including energy necessary for basic functions, such as breathing and heartbeat Broccoli (1 cup) 25 (a) Food Calories (kilocalories) in various foods (b) Food Calories (kilocalories) we burn in various activities Figure 5.3 Figure 5.3 Some caloric accounting

Energy Transformations: ATP and Cellular Work
Chemical energy released by the breakdown of organic molecules during cellular respiration is used to generate molecules of ATP. ATP acts like an energy shuttle, stores energy obtained from food, and releases it later as needed. Such energy transformations are essential for all life on Earth. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Although students might already understand mechanical and chemical work in a cell, the idea of transport work might be new to them. Chapter 6, in a section on the electron transport system, develops an analogy between transport work and water behind a dam. Therefore, at this point you might consider making an analogy between transport work (against a gradient) and pumping water up into a reservoir (against gravity)—perhaps into a water tower. 2. Energy shuttling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from your employer. (Most of us would soon tire of a fast-food job that pays its employees only in free food!) Money permits the generation of value (a paycheck) analogous to an energy-releasing reaction to be coupled to an energy (money)-consuming reaction, making purchases in distant locations. This idea of “earn and spend” is a common concept most students know well. Teaching Tips 1. The authors suggest an analogy between ATP and a spring. When a phosphate group is attached to ADP, it is like compressing the spring. When a phosphate group is lost, the spring is relaxed, and energy is released. 2. When introducing ATP and ADP, consider having students think of the terms as A-3-P and A-2-P, noting that the word roots “tri” means three and “di” means two. It might help students to keep track of the number of phosphates more easily. 3. Recycling is essential in cell biology. Damaged organelles are broken down intracellularly and the chemical components recycled, monomers of the cytoskeleton are routinely recycled, and ADP is recycled. Several advantages are common to both human recycling of components of garbage and cellular recycling. For example, both save energy by avoiding the need to remanufacture the basic units, and both avoid an accumulation of waste products that could interfere with other “environmental” chemistry (the environment of the cell or the environment of the human population). Active Lecture Tips 1. See the Activity Universal Currency in the Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 21

The Structure of ATP ATP (adenosine triphosphate)
consists of an organic molecule called adenosine plus a tail of three phosphate groups and is broken down to ADP, adenosine diphosphate, and a phosphate group, releasing energy. The release of the phosphate at the tip of the triphosphate tail makes energy available to cells. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Although students might already understand mechanical and chemical work in a cell, the idea of transport work might be new to them. Chapter 6, in a section on the electron transport system, develops an analogy between transport work and water behind a dam. Therefore, at this point you might consider making an analogy between transport work (against a gradient) and pumping water up into a reservoir (against gravity)—perhaps into a water tower. 2. Energy shuttling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from your employer. (Most of us would soon tire of a fast-food job that pays its employees only in free food!) Money permits the generation of value (a paycheck) analogous to an energy-releasing reaction to be coupled to an energy (money)-consuming reaction, making purchases in distant locations. This idea of “earn and spend” is a common concept most students know well. Teaching Tips 1. The authors suggest an analogy between ATP and a spring. When a phosphate group is attached to ADP, it is like compressing the spring. When a phosphate group is lost, the spring is relaxed, and energy is released. 2. When introducing ATP and ADP, consider having students think of the terms as A-3-P and A-2-P, noting that the word roots “tri” means three and “di” means two. It might help students to keep track of the number of phosphates more easily. 3. Recycling is essential in cell biology. Damaged organelles are broken down intracellularly and the chemical components recycled, monomers of the cytoskeleton are routinely recycled, and ADP is recycled. Several advantages are common to both human recycling of components of garbage and cellular recycling. For example, both save energy by avoiding the need to remanufacture the basic units, and both avoid an accumulation of waste products that could interfere with other “environmental” chemistry (the environment of the cell or the environment of the human population). Active Lecture Tips 1. See the Activity Universal Currency in the Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 22

ATP power Energy Triphosphate Diphosphate Adenosine P P P Adenosine P
(transferred to another molecule) ATP ADP Figure 5.4 Figure 5.4 ATP power

Phosphate Transfer ATP energizes other molecules in cells by transferring phosphate groups to those molecules. This energy helps cells change shape (Mechanical work) enables the transport of ions and other dissolved substances across the membranes (Transport work), and drives the production of a cell’s large molecules (Chemical work). © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Although students might already understand mechanical and chemical work in a cell, the idea of transport work might be new to them. Chapter 6, in a section on the electron transport system, develops an analogy between transport work and water behind a dam. Therefore, at this point you might consider making an analogy between transport work (against a gradient) and pumping water up into a reservoir (against gravity)—perhaps into a water tower. 2. Energy shuttling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from your employer. (Most of us would soon tire of a fast-food job that pays its employees only in free food!) Money permits the generation of value (a paycheck) analogous to an energy-releasing reaction to be coupled to an energy (money)-consuming reaction, making purchases in distant locations. This idea of “earn and spend” is a common concept most students know well. Teaching Tips 1. The authors suggest an analogy between ATP and a spring. When a phosphate group is attached to ADP, it is like compressing the spring. When a phosphate group is lost, the spring is relaxed, and energy is released. 2. When introducing ATP and ADP, consider having students think of the terms as A-3-P and A-2-P, noting that the word roots “tri” means three and “di” means two. It might help students to keep track of the number of phosphates more easily. 3. Recycling is essential in cell biology. Damaged organelles are broken down intracellularly and the chemical components recycled, monomers of the cytoskeleton are routinely recycled, and ADP is recycled. Several advantages are common to both human recycling of components of garbage and cellular recycling. For example, both save energy by avoiding the need to remanufacture the basic units, and both avoid an accumulation of waste products that could interfere with other “environmental” chemistry (the environment of the cell or the environment of the human population). Active Lecture Tips 1. See the Activity Universal Currency in the Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 24

(a) Motor protein performing mechanical work (moving a muscle fiber)
ATP ADP P ADP P Protein moved (a) Motor protein performing mechanical work (moving a muscle fiber) Solute Transport protein P P ATP ADP P Solute transported (b) Transport protein performing transport work (importing a solute) P ATP X P X Y ADP P Y Reactants Product made (c) Chemical reactants performing chemical work (promoting a chemical reaction) Figure 5.5 Figure 5.5 How ATP drives cellular work

The ATP Cycle Cells spend ATP continuously.
ATP is recycled when ADP and phosphate are combined, using energy released by cellular respiration. Up to 10 million ATPs are consumed and recycled each second in a working muscle cell. Cellular respiration: chemical energy harvested from fuel molecules Energy for cellular work ATP ADP P © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. Although students might already understand mechanical and chemical work in a cell, the idea of transport work might be new to them. Chapter 6, in a section on the electron transport system, develops an analogy between transport work and water behind a dam. Therefore, at this point you might consider making an analogy between transport work (against a gradient) and pumping water up into a reservoir (against gravity)—perhaps into a water tower. 2. Energy shuttling at the cellular level may be new to many students, but it is a familiar concept when related to the use of money in our society. Students might be discouraged if the only benefit of work was the ability to make purchases from your employer. (Most of us would soon tire of a fast-food job that pays its employees only in free food!) Money permits the generation of value (a paycheck) analogous to an energy-releasing reaction to be coupled to an energy (money)-consuming reaction, making purchases in distant locations. This idea of “earn and spend” is a common concept most students know well. Teaching Tips 1. The authors suggest an analogy between ATP and a spring. When a phosphate group is attached to ADP, it is like compressing the spring. When a phosphate group is lost, the spring is relaxed, and energy is released. 2. When introducing ATP and ADP, consider having students think of the terms as A-3-P and A-2-P, noting that the word roots “tri” means three and “di” means two. It might help students to keep track of the number of phosphates more easily. 3. Recycling is essential in cell biology. Damaged organelles are broken down intracellularly and the chemical components recycled, monomers of the cytoskeleton are routinely recycled, and ADP is recycled. Several advantages are common to both human recycling of components of garbage and cellular recycling. For example, both save energy by avoiding the need to remanufacture the basic units, and both avoid an accumulation of waste products that could interfere with other “environmental” chemistry (the environment of the cell or the environment of the human population). Active Lecture Tips 1. See the Activity Universal Currency in the Cell on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 26

ENZYMES Metabolism is the total of all chemical reactions in an organism. Most metabolic reactions require the assistance of enzymes, proteins that speed up chemical reactions without being consumed by the reaction. All living cells contain thousands of different enzymes, each promoting a different chemical reaction. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. For students not previously familiar with activation energy, analogies can make all the difference. Activation energy can be thought of as a small input that is needed to trigger a large output. This is like (a) an irritated person who needs only a bit more frustration to explode in anger, (b) small waves that lift debris over a dam, or (c) lighting a match around lighter fluid. In each situation, the output was much greater than the input. 2. The specific interactions of enzymes and substrates can be illustrated with simple physical models. Many students new to these concepts will benefit from several forms of explanation, including diagrams such as those in the textbook, physical models, and the opportunity to manipulate or create their own examples. New concepts, like pitching a tent, are best constructed with many lines of support. Teaching Tips 1. The text notes that the relationship between an enzyme and its substrate is like a handshake, with each hand generally conforming to the shape of the other. This induced fit is also like the change in shape of a glove when a hand is inserted. The glove’s general shape matches the hand, but the final “fit” requires some additional adjustments. 2. Enzyme inhibitors that block the active site are like (a) a person sitting in your assigned theater seat or (b) a car parked in your parking space. Analogies for inhibitors that change the shape of the active site are more difficult to imagine. Consider challenging your students to think of such analogies. (Perhaps someone adjusting the driver seat of the car differently from your preferences and then leaving it that way when you try to use the car.) 3. Consider challenging your class to suggest advantages to using specific enzyme inhibitors as insect poisons. Many advantages exist and include (a) the ability to target chemical reactions of only certain types of pest organisms and (b) the ability to target chemical reactions that are found in insects but not in humans. 4. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. Yet in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might be curious, and you could point out that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, which are proteins with the ability to control the production of carbohydrates and lipids. Active Lecture Tips 1. Feedback regulation relies on the negative feedback of the accumulation of a product. Ask students in class to work in pairs to suggest other products of reactions that inhibit the process that made them, when the product reaches high enough levels. (Gas station pumps routinely shut off when a high level of gasoline is detected. Furnaces typically turn off when enough heat has been produced, and toilets stop running when the tank is refilled.) 2. See the Activity Students, Design Your Own Enzyme-Catalyzed Reaction on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. See the Activity Lock and Key Analogy with Enzymes on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 27

Activation Energy A chemical reaction begins with chemical bonds in the reactant molecules being broken. This process requires that molecules absorb energy from their surroundings; this is called activation energy, because it activates the reactants & triggers the chemical reaction Activation energy is the energy that must be invested to start a reaction, by activating the reactants and triggering a chemical reaction. Enzymes enable metabolism to occur by reducing the amount of activation energy required to break the bonds of reactant molecules. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. For students not previously familiar with activation energy, analogies can make all the difference. Activation energy can be thought of as a small input that is needed to trigger a large output. This is like (a) an irritated person who needs only a bit more frustration to explode in anger, (b) small waves that lift debris over a dam, or (c) lighting a match around lighter fluid. In each situation, the output was much greater than the input. 2. The specific interactions of enzymes and substrates can be illustrated with simple physical models. Many students new to these concepts will benefit from several forms of explanation, including diagrams such as those in the textbook, physical models, and the opportunity to manipulate or create their own examples. New concepts, like pitching a tent, are best constructed with many lines of support. Teaching Tips 1. The text notes that the relationship between an enzyme and its substrate is like a handshake, with each hand generally conforming to the shape of the other. This induced fit is also like the change in shape of a glove when a hand is inserted. The glove’s general shape matches the hand, but the final “fit” requires some additional adjustments. 2. Enzyme inhibitors that block the active site are like (a) a person sitting in your assigned theater seat or (b) a car parked in your parking space. Analogies for inhibitors that change the shape of the active site are more difficult to imagine. Consider challenging your students to think of such analogies. (Perhaps someone adjusting the driver seat of the car differently from your preferences and then leaving it that way when you try to use the car.) 3. Consider challenging your class to suggest advantages to using specific enzyme inhibitors as insect poisons. Many advantages exist and include (a) the ability to target chemical reactions of only certain types of pest organisms and (b) the ability to target chemical reactions that are found in insects but not in humans. 4. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. Yet in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might be curious, and you could point out that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, which are proteins with the ability to control the production of carbohydrates and lipids. Active Lecture Tips 1. Feedback regulation relies on the negative feedback of the accumulation of a product. Ask students in class to work in pairs to suggest other products of reactions that inhibit the process that made them, when the product reaches high enough levels. (Gas station pumps routinely shut off when a high level of gasoline is detected. Furnaces typically turn off when enough heat has been produced, and toilets stop running when the tank is refilled.) 2. See the Activity Students, Design Your Own Enzyme-Catalyzed Reaction on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. See the Activity Lock and Key Analogy with Enzymes on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 28

Enzymes and activation energy
energy barrier Activation energy barrier reduced by enzyme Enzyme Reactant Reactant Energy level Energy level Products Products (a) Without enzyme (b) With enzyme Figure 5.7 Enzymes and activation energy

Structure/Function: Enzyme Activity
An enzyme is very selective in the reaction it catalyzes. Each enzyme recognizes a substrate, a certain reactant molecule. The active site has a shape and chemistry that fits the substrate molecule. This interaction is called induced fit because the entry of the substrate induces the enzyme to change shape slightly, making the fit between the substrate and active site snugger. Enzymes can function over and over again, a key characteristic of enzymes. Many enzymes are named for their substrates, but with an –ase ending. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. For students not previously familiar with activation energy, analogies can make all the difference. Activation energy can be thought of as a small input that is needed to trigger a large output. This is like (a) an irritated person who needs only a bit more frustration to explode in anger, (b) small waves that lift debris over a dam, or (c) lighting a match around lighter fluid. In each situation, the output was much greater than the input. 2. The specific interactions of enzymes and substrates can be illustrated with simple physical models. Many students new to these concepts will benefit from several forms of explanation, including diagrams such as those in the textbook, physical models, and the opportunity to manipulate or create their own examples. New concepts, like pitching a tent, are best constructed with many lines of support. Teaching Tips 1. The text notes that the relationship between an enzyme and its substrate is like a handshake, with each hand generally conforming to the shape of the other. This induced fit is also like the change in shape of a glove when a hand is inserted. The glove’s general shape matches the hand, but the final “fit” requires some additional adjustments. 2. Enzyme inhibitors that block the active site are like (a) a person sitting in your assigned theater seat or (b) a car parked in your parking space. Analogies for inhibitors that change the shape of the active site are more difficult to imagine. Consider challenging your students to think of such analogies. (Perhaps someone adjusting the driver seat of the car differently from your preferences and then leaving it that way when you try to use the car.) 3. Consider challenging your class to suggest advantages to using specific enzyme inhibitors as insect poisons. Many advantages exist and include (a) the ability to target chemical reactions of only certain types of pest organisms and (b) the ability to target chemical reactions that are found in insects but not in humans. 4. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. Yet in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might be curious, and you could point out that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, which are proteins with the ability to control the production of carbohydrates and lipids. Active Lecture Tips 1. Feedback regulation relies on the negative feedback of the accumulation of a product. Ask students in class to work in pairs to suggest other products of reactions that inhibit the process that made them, when the product reaches high enough levels. (Gas station pumps routinely shut off when a high level of gasoline is detected. Furnaces typically turn off when enough heat has been produced, and toilets stop running when the tank is refilled.) 2. See the Activity Students, Design Your Own Enzyme-Catalyzed Reaction on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. See the Activity Lock and Key Analogy with Enzymes on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 30

Animation: How Enzymes Work

How an enzyme works 1 Substrate (lactose) Ready for substrate
Active site 2 Substrate binding Enzyme (lactase) Galactose H2O Glucose 4 Product release 3 Catalysis Figure 5.9-s4 Figure 5.9-s4 How an enzyme works (step 4)

Enzyme Inhibitors Certain molecules inhibit a metabolic reaction by
binding to an enzyme and disrupting its function. Some of these enzyme inhibitors are actually substrate imposters that plug up the active site. Other inhibitors bind to the enzyme at a site remote from the active site, but the binding changes the enzyme’s shape so that the active site no longer accepts the substrate. In each case, an inhibitor disrupts the function of an enzyme by altering its shape. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. For students not previously familiar with activation energy, analogies can make all the difference. Activation energy can be thought of as a small input that is needed to trigger a large output. This is like (a) an irritated person who needs only a bit more frustration to explode in anger, (b) small waves that lift debris over a dam, or (c) lighting a match around lighter fluid. In each situation, the output was much greater than the input. 2. The specific interactions of enzymes and substrates can be illustrated with simple physical models. Many students new to these concepts will benefit from several forms of explanation, including diagrams such as those in the textbook, physical models, and the opportunity to manipulate or create their own examples. New concepts, like pitching a tent, are best constructed with many lines of support. Teaching Tips 1. The text notes that the relationship between an enzyme and its substrate is like a handshake, with each hand generally conforming to the shape of the other. This induced fit is also like the change in shape of a glove when a hand is inserted. The glove’s general shape matches the hand, but the final “fit” requires some additional adjustments. 2. Enzyme inhibitors that block the active site are like (a) a person sitting in your assigned theater seat or (b) a car parked in your parking space. Analogies for inhibitors that change the shape of the active site are more difficult to imagine. Consider challenging your students to think of such analogies. (Perhaps someone adjusting the driver seat of the car differently from your preferences and then leaving it that way when you try to use the car.) 3. Consider challenging your class to suggest advantages to using specific enzyme inhibitors as insect poisons. Many advantages exist and include (a) the ability to target chemical reactions of only certain types of pest organisms and (b) the ability to target chemical reactions that are found in insects but not in humans. 4. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. Yet in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might be curious, and you could point out that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, which are proteins with the ability to control the production of carbohydrates and lipids. Active Lecture Tips 1. Feedback regulation relies on the negative feedback of the accumulation of a product. Ask students in class to work in pairs to suggest other products of reactions that inhibit the process that made them, when the product reaches high enough levels. (Gas station pumps routinely shut off when a high level of gasoline is detected. Furnaces typically turn off when enough heat has been produced, and toilets stop running when the tank is refilled.) 2. See the Activity Students, Design Your Own Enzyme-Catalyzed Reaction on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. See the Activity Lock and Key Analogy with Enzymes on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 33

Enzyme inhibitors (a) Enzyme and substrate binding normally
Active site Enzyme inhibitors Enzyme (b) Enzyme inhibition by a substrate imposter Inhibitor Substrate Active site Enzyme (c) Inhibition of an enzyme by a molecule that causes the active site to change shape Substrate Active site Inhibitor Enzyme Figure 5.10 Figure 5.10 Enzyme inhibitors

Enzyme Inhibitors In some cases, the binding of an inhibitor s reversible. If a cell is producing more of a certain product than it needs, that product may reversibly inhibit an enzyme required for its production, keeping the cell from wasting resources that could be put to better use. Many beneficial drugs work by inhibiting enzymes. Penicillin blocks the active site of an enzyme that bacteria use in making cell walls. Ibuprofen inhibits an enzyme involved in sending pain signals. Many cancer drugs inhibit enzymes that promote cell division. Many toxins and poisons also work as inhibitors. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. For students not previously familiar with activation energy, analogies can make all the difference. Activation energy can be thought of as a small input that is needed to trigger a large output. This is like (a) an irritated person who needs only a bit more frustration to explode in anger, (b) small waves that lift debris over a dam, or (c) lighting a match around lighter fluid. In each situation, the output was much greater than the input. 2. The specific interactions of enzymes and substrates can be illustrated with simple physical models. Many students new to these concepts will benefit from several forms of explanation, including diagrams such as those in the textbook, physical models, and the opportunity to manipulate or create their own examples. New concepts, like pitching a tent, are best constructed with many lines of support. Teaching Tips 1. The text notes that the relationship between an enzyme and its substrate is like a handshake, with each hand generally conforming to the shape of the other. This induced fit is also like the change in shape of a glove when a hand is inserted. The glove’s general shape matches the hand, but the final “fit” requires some additional adjustments. 2. Enzyme inhibitors that block the active site are like (a) a person sitting in your assigned theater seat or (b) a car parked in your parking space. Analogies for inhibitors that change the shape of the active site are more difficult to imagine. Consider challenging your students to think of such analogies. (Perhaps someone adjusting the driver seat of the car differently from your preferences and then leaving it that way when you try to use the car.) 3. Consider challenging your class to suggest advantages to using specific enzyme inhibitors as insect poisons. Many advantages exist and include (a) the ability to target chemical reactions of only certain types of pest organisms and (b) the ability to target chemical reactions that are found in insects but not in humans. 4. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. Yet in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might be curious, and you could point out that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, which are proteins with the ability to control the production of carbohydrates and lipids. Active Lecture Tips 1. Feedback regulation relies on the negative feedback of the accumulation of a product. Ask students in class to work in pairs to suggest other products of reactions that inhibit the process that made them, when the product reaches high enough levels. (Gas station pumps routinely shut off when a high level of gasoline is detected. Furnaces typically turn off when enough heat has been produced, and toilets stop running when the tank is refilled.) 2. See the Activity Students, Design Your Own Enzyme-Catalyzed Reaction on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. See the Activity Lock and Key Analogy with Enzymes on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 35

MEMBRANE FUNCTION Working cells must control the flow of materials to and from the environment Cell membrane separates living cell from aqueous environment thin barrier = 8nm thick controls traffic in & out of the cell allows some substances to cross more easily than others hydrophobic (nonpolar) vs. hydrophilic (polar) The plasma membrane consists of a double layer of fat (a phospholipid bilayer) with embedded proteins. Membrane proteins perform many functions Transport proteins are located in membranes, they regulate the passage of materials into and out of the cell So far we learned about how cells control the flow of energy and the pace of chemical ractions. They also must control the flow of materials to and from the environment

Permeability to polar molecules?
Phospholipid bilayer - Serves as a cellular barrier / border Transmembrane proteins embedded in phospholipid bilayer - specific channels allow specific material across cell membrane Membrane becomes semi-permeable via protein channels Fluid Mosaic model: Fluid: Phospholipids have fluid consistency like that of oil Mosaic: Proteins are scattered throughout Function: Maintains the cell’s shape, Regulates what goes into and out of cell inside cell H2O aa sugar Polar hydrophilic heads Nonpolar Hydrophobic tails Polar hydrophilic heads outside cell salt NH3

Practice Which of the following describes the fluid-mosaic model of the plasma membrane structure? phospholipid monolayer with embedded proteins phospholipid bilayer with embedded proteins C) phospholipid trilayer with embedded proteins D) triglyceride bilayer with embedded proteins E) triglyceride monolayer with embedded proteins

Practice Which of the following is NOT a characteristic of an animal plasma membrane? A) separates the internal environment of the cell from the external environment B) helps the cell maintain homeostasis C) responsible for the synthesis of ATP D) helps to maintain the cell's shape E) regulates passage of molecules into and out of the cell

Primary functions of membrane proteins
Cell signaling Enzymatic activity Fibers of extracellular matrix Cytoplasm Cytoplasm Cytoskeleton Attachment to the cytoskeleton and extracellular matrix Transport Intercellular joining Cell-cell recognition Figure 5.11 Figure 5.11 Primary functions of membrane proteins

BioFlix Animation: Membrane Transport

Passive Transport: Diffusion across Membranes
Molecules contain heat energy that causes them to constantly vibrate and wander randomly. Diffusion is the movement of molecules spreading out evenly into the available space. Imagine a membrane separating pure water from a mixture of dye dissolved in water. Passive transport is the diffusion of a substance across a membrane without the input of energy (O2 and CO2). In passive transport, a substance diffuses down its concentration gradient from where the substance is more concentrated to where it is less concentrated. Student Misconceptions and Concerns 1. For students with limited science backgrounds, concepts such as diffusion and osmosis can take considerable time to fully understand and apply. Instructors often struggle to remember a time in their lives when they did not know about such fundamental scientific principles. Consider spending extra time to illustrate and demonstrate these key processes to the class. Consider short interactive class exercises in which students create analogies or think of examples of these principles in their lives. 2. Students easily confuse the terms hypertonic and hypotonic. One challenge is to understand that these are relative terms, such as heavier, darker, or fewer. No single solution is “heavier,” no single cup of coffee is “darker,” and no single bag of M & M’s has “fewer” candies. Such terms only apply when comparing two or more items. A solution with a higher concentration is “hypertonic.” But the same solution might also be “hypotonic” to a third solution. Teaching Tips 1. Students often benefit from reminders of diffusion in their lives. Smells can usually be traced back to their sources—the smell of dinner on the stove, the scent of a perfume or cologne coming from its bottle, the smoke drifting away from a campfire. These scents are strongest nearest the source and weaker as we move away. 2. The word root “hypo” means “below.” Thus, a hypodermic needle injects substances below the dermis. Students might best remember that hypotonic solutions have concentrations below that of the other solution(s). 3. After introducing the idea of hypertonic and hypotonic solutions, you may wish to challenge your students with the following: A marine salmon moves from the ocean up a freshwater stream to reproduce. The salmon is moving from a _____ environment to a _____ environment. (Answers: hypertonic; hypotonic) 4. Your students may have noticed that their fingers wrinkle after taking a long shower or bath or washing dishes. The skin wrinkles because it is swollen with water but still tacked down at some points. Oils inhibit the movement of water into our skin. Thus, soapy water results in wrinkling faster than plain water since the soap removes the natural layer of oil from our skin. Our skin is hypertonic to the solutions that produce the swelling that appears as large wrinkles. 5. The effects of hypertonic and hypotonic solutions are easily demonstrated if students soak carrot sticks, long slices of potato, or celery in hypertonic and hypotonic solutions. These also make nice class demonstrations. 6. The hydrophobic and hydrophilic ends of a phospholipid molecule create a lipid bilayer. The hydrophobic edges of the layer will also seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water. Furthermore, because of these hydrophobic properties, lipid bilayers are naturally self-healing. All of these properties emerge from the structure of phospholipid. Active Lecture Tips 1. Consider demonstrating simple diffusion. A large jar of water and a few drops of dark-colored dye work well over the course of a lecture period. Alternatively, release a strong scent of cologne or peppermint or peel part of an orange in the classroom and have students raise their hands as they first detect the smell. Students nearest the source will raise their hands before students farther away. A fan from a projector or overhead vent may bias the experiment a bit, so be aware of any directed movements of air in your classroom that might disrupt this demonstration. 2. See the Activity Using Food and Drink to Describe Osmosis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. Students carefully considering exocytosis may notice that membrane from secretory vesicles is added to the plasma membrane. Challenge your students to work with someone sitting nearby to identify mechanisms that balance out this enlargement of the cell surface. (Endocytosis “subtracts” area from the cell surface. It is a major factor balancing out the additional membrane supplied by exocytosis.) 42

Passive transport: diffusion across a membrane
Molecules of dye Membrane (a) Passive transport of one type of molecule (b) Passive transport of two types of molecules Net diffusion Equilibrium Figure 5.12 Passive transport: diffusion across a membrane A substance will diffuse from where it is more concentrated to where it is less concentrated which mean substances diffuse down their concentration gradient. Passive transport of two types of molecules” each will diffuse down its own concentratrion gradient.

Passive Transport: Diffusion across Membranes
Substances that do not cross membranes spontaneously, or otherwise cross very slowly, can be transported via proteins that act as corridors for specific molecules. This assisted transport is called facilitated diffusion, a type of passive transport because it does not require the cell to expend energy. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. For students with limited science backgrounds, concepts such as diffusion and osmosis can take considerable time to fully understand and apply. Instructors often struggle to remember a time in their lives when they did not know about such fundamental scientific principles. Consider spending extra time to illustrate and demonstrate these key processes to the class. Consider short interactive class exercises in which students create analogies or think of examples of these principles in their lives. 2. Students easily confuse the terms hypertonic and hypotonic. One challenge is to understand that these are relative terms, such as heavier, darker, or fewer. No single solution is “heavier,” no single cup of coffee is “darker,” and no single bag of M & M’s has “fewer” candies. Such terms only apply when comparing two or more items. A solution with a higher concentration is “hypertonic.” But the same solution might also be “hypotonic” to a third solution. Teaching Tips 1. Students often benefit from reminders of diffusion in their lives. Smells can usually be traced back to their sources—the smell of dinner on the stove, the scent of a perfume or cologne coming from its bottle, the smoke drifting away from a campfire. These scents are strongest nearest the source and weaker as we move away. 2. The word root “hypo” means “below.” Thus, a hypodermic needle injects substances below the dermis. Students might best remember that hypotonic solutions have concentrations below that of the other solution(s). 3. After introducing the idea of hypertonic and hypotonic solutions, you may wish to challenge your students with the following: A marine salmon moves from the ocean up a freshwater stream to reproduce. The salmon is moving from a _____ environment to a _____ environment. (Answers: hypertonic; hypotonic) 4. Your students may have noticed that their fingers wrinkle after taking a long shower or bath or washing dishes. The skin wrinkles because it is swollen with water but still tacked down at some points. Oils inhibit the movement of water into our skin. Thus, soapy water results in wrinkling faster than plain water since the soap removes the natural layer of oil from our skin. Our skin is hypertonic to the solutions that produce the swelling that appears as large wrinkles. 5. The effects of hypertonic and hypotonic solutions are easily demonstrated if students soak carrot sticks, long slices of potato, or celery in hypertonic and hypotonic solutions. These also make nice class demonstrations. 6. The hydrophobic and hydrophilic ends of a phospholipid molecule create a lipid bilayer. The hydrophobic edges of the layer will also seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water. Furthermore, because of these hydrophobic properties, lipid bilayers are naturally self-healing. All of these properties emerge from the structure of phospholipid. Active Lecture Tips 1. Consider demonstrating simple diffusion. A large jar of water and a few drops of dark-colored dye work well over the course of a lecture period. Alternatively, release a strong scent of cologne or peppermint or peel part of an orange in the classroom and have students raise their hands as they first detect the smell. Students nearest the source will raise their hands before students farther away. A fan from a projector or overhead vent may bias the experiment a bit, so be aware of any directed movements of air in your classroom that might disrupt this demonstration. 2. See the Activity Using Food and Drink to Describe Osmosis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. Students carefully considering exocytosis may notice that membrane from secretory vesicles is added to the plasma membrane. Challenge your students to work with someone sitting nearby to identify mechanisms that balance out this enlargement of the cell surface. (Endocytosis “subtracts” area from the cell surface. It is a major factor balancing out the additional membrane supplied by exocytosis.) 45

Osmosis and Water Balance
The diffusion of water across a selectively permeable membrane is osmosis (special kind of passive transport). A solute is a substance that is dissolved in a liquid solvent, such as the salt in salt water, and the resulting mixture is called a solution. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. For students with limited science backgrounds, concepts such as diffusion and osmosis can take considerable time to fully understand and apply. Instructors often struggle to remember a time in their lives when they did not know about such fundamental scientific principles. Consider spending extra time to illustrate and demonstrate these key processes to the class. Consider short interactive class exercises in which students create analogies or think of examples of these principles in their lives. 2. Students easily confuse the terms hypertonic and hypotonic. One challenge is to understand that these are relative terms, such as heavier, darker, or fewer. No single solution is “heavier,” no single cup of coffee is “darker,” and no single bag of M & M’s has “fewer” candies. Such terms only apply when comparing two or more items. A solution with a higher concentration is “hypertonic.” But the same solution might also be “hypotonic” to a third solution. Teaching Tips 1. Students often benefit from reminders of diffusion in their lives. Smells can usually be traced back to their sources—the smell of dinner on the stove, the scent of a perfume or cologne coming from its bottle, the smoke drifting away from a campfire. These scents are strongest nearest the source and weaker as we move away. 2. The word root “hypo” means “below.” Thus, a hypodermic needle injects substances below the dermis. Students might best remember that hypotonic solutions have concentrations below that of the other solution(s). 3. After introducing the idea of hypertonic and hypotonic solutions, you may wish to challenge your students with the following: A marine salmon moves from the ocean up a freshwater stream to reproduce. The salmon is moving from a _____ environment to a _____ environment. (Answers: hypertonic; hypotonic) 4. Your students may have noticed that their fingers wrinkle after taking a long shower or bath or washing dishes. The skin wrinkles because it is swollen with water but still tacked down at some points. Oils inhibit the movement of water into our skin. Thus, soapy water results in wrinkling faster than plain water since the soap removes the natural layer of oil from our skin. Our skin is hypertonic to the solutions that produce the swelling that appears as large wrinkles. 5. The effects of hypertonic and hypotonic solutions are easily demonstrated if students soak carrot sticks, long slices of potato, or celery in hypertonic and hypotonic solutions. These also make nice class demonstrations. 6. The hydrophobic and hydrophilic ends of a phospholipid molecule create a lipid bilayer. The hydrophobic edges of the layer will also seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water. Furthermore, because of these hydrophobic properties, lipid bilayers are naturally self-healing. All of these properties emerge from the structure of phospholipid. Active Lecture Tips 1. Consider demonstrating simple diffusion. A large jar of water and a few drops of dark-colored dye work well over the course of a lecture period. Alternatively, release a strong scent of cologne or peppermint or peel part of an orange in the classroom and have students raise their hands as they first detect the smell. Students nearest the source will raise their hands before students farther away. A fan from a projector or overhead vent may bias the experiment a bit, so be aware of any directed movements of air in your classroom that might disrupt this demonstration. 2. See the Activity Using Food and Drink to Describe Osmosis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. Students carefully considering exocytosis may notice that membrane from secretory vesicles is added to the plasma membrane. Challenge your students to work with someone sitting nearby to identify mechanisms that balance out this enlargement of the cell surface. (Endocytosis “subtracts” area from the cell surface. It is a major factor balancing out the additional membrane supplied by exocytosis.) 46

The diffusion of water across a selectively permeable membrane is osmosis (special kind of passive transport). The membrane allows water to pass but not the solute. the solution with the higher concentration is hypertonic and the one with lower solute is hypotonic. Lower concentration (Hypotonic solution) Higher concentration (Hypertonic solution) Sugar molecule Selectively permeable membrane Osmosis Equal concentration (Isotonic solutions) People can take the advantage of osmosis to preserve foods.

Direction of osmosis is determined by comparing total solute concentrations Compared to another solution, a hypertonic solution has a higher concentration of solute than the cell, a hypotonic solution has a lower concentration of solute than the cell, and an isotonic solution has an equal concentration of solute with the cell. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. For students with limited science backgrounds, concepts such as diffusion and osmosis can take considerable time to fully understand and apply. Instructors often struggle to remember a time in their lives when they did not know about such fundamental scientific principles. Consider spending extra time to illustrate and demonstrate these key processes to the class. Consider short interactive class exercises in which students create analogies or think of examples of these principles in their lives. 2. Students easily confuse the terms hypertonic and hypotonic. One challenge is to understand that these are relative terms, such as heavier, darker, or fewer. No single solution is “heavier,” no single cup of coffee is “darker,” and no single bag of M & M’s has “fewer” candies. Such terms only apply when comparing two or more items. A solution with a higher concentration is “hypertonic.” But the same solution might also be “hypotonic” to a third solution. Teaching Tips 1. Students often benefit from reminders of diffusion in their lives. Smells can usually be traced back to their sources—the smell of dinner on the stove, the scent of a perfume or cologne coming from its bottle, the smoke drifting away from a campfire. These scents are strongest nearest the source and weaker as we move away. 2. The word root “hypo” means “below.” Thus, a hypodermic needle injects substances below the dermis. Students might best remember that hypotonic solutions have concentrations below that of the other solution(s). 3. After introducing the idea of hypertonic and hypotonic solutions, you may wish to challenge your students with the following: A marine salmon moves from the ocean up a freshwater stream to reproduce. The salmon is moving from a _____ environment to a _____ environment. (Answers: hypertonic; hypotonic) 4. Your students may have noticed that their fingers wrinkle after taking a long shower or bath or washing dishes. The skin wrinkles because it is swollen with water but still tacked down at some points. Oils inhibit the movement of water into our skin. Thus, soapy water results in wrinkling faster than plain water since the soap removes the natural layer of oil from our skin. Our skin is hypertonic to the solutions that produce the swelling that appears as large wrinkles. 5. The effects of hypertonic and hypotonic solutions are easily demonstrated if students soak carrot sticks, long slices of potato, or celery in hypertonic and hypotonic solutions. These also make nice class demonstrations. 6. The hydrophobic and hydrophilic ends of a phospholipid molecule create a lipid bilayer. The hydrophobic edges of the layer will also seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water. Furthermore, because of these hydrophobic properties, lipid bilayers are naturally self-healing. All of these properties emerge from the structure of phospholipid. Active Lecture Tips 1. Consider demonstrating simple diffusion. A large jar of water and a few drops of dark-colored dye work well over the course of a lecture period. Alternatively, release a strong scent of cologne or peppermint or peel part of an orange in the classroom and have students raise their hands as they first detect the smell. Students nearest the source will raise their hands before students farther away. A fan from a projector or overhead vent may bias the experiment a bit, so be aware of any directed movements of air in your classroom that might disrupt this demonstration. 2. See the Activity Using Food and Drink to Describe Osmosis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. Students carefully considering exocytosis may notice that membrane from secretory vesicles is added to the plasma membrane. Challenge your students to work with someone sitting nearby to identify mechanisms that balance out this enlargement of the cell surface. (Endocytosis “subtracts” area from the cell surface. It is a major factor balancing out the additional membrane supplied by exocytosis.) 49

Water Balance in Animal Cells
The survival of a cell depends on its ability to balance water uptake and loss. For an animal to survive a hypotonic or hypertonic environment, the animal must have a way to balance the uptake and loss of water. The control of water balance is called osmoregulation. Most animal cells require an isotonic environment Plant have rigid cell walls. They require a hypotonic environment, which expands their cell walls without bursting which keeps these walled cells turgid © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. For students with limited science backgrounds, concepts such as diffusion and osmosis can take considerable time to fully understand and apply. Instructors often struggle to remember a time in their lives when they did not know about such fundamental scientific principles. Consider spending extra time to illustrate and demonstrate these key processes to the class. Consider short interactive class exercises in which students create analogies or think of examples of these principles in their lives. 2. Students easily confuse the terms hypertonic and hypotonic. One challenge is to understand that these are relative terms, such as heavier, darker, or fewer. No single solution is “heavier,” no single cup of coffee is “darker,” and no single bag of M & M’s has “fewer” candies. Such terms only apply when comparing two or more items. A solution with a higher concentration is “hypertonic.” But the same solution might also be “hypotonic” to a third solution. Teaching Tips 1. Students often benefit from reminders of diffusion in their lives. Smells can usually be traced back to their sources—the smell of dinner on the stove, the scent of a perfume or cologne coming from its bottle, the smoke drifting away from a campfire. These scents are strongest nearest the source and weaker as we move away. 2. The word root “hypo” means “below.” Thus, a hypodermic needle injects substances below the dermis. Students might best remember that hypotonic solutions have concentrations below that of the other solution(s). 3. After introducing the idea of hypertonic and hypotonic solutions, you may wish to challenge your students with the following: A marine salmon moves from the ocean up a freshwater stream to reproduce. The salmon is moving from a _____ environment to a _____ environment. (Answers: hypertonic; hypotonic) 4. Your students may have noticed that their fingers wrinkle after taking a long shower or bath or washing dishes. The skin wrinkles because it is swollen with water but still tacked down at some points. Oils inhibit the movement of water into our skin. Thus, soapy water results in wrinkling faster than plain water since the soap removes the natural layer of oil from our skin. Our skin is hypertonic to the solutions that produce the swelling that appears as large wrinkles. 5. The effects of hypertonic and hypotonic solutions are easily demonstrated if students soak carrot sticks, long slices of potato, or celery in hypertonic and hypotonic solutions. These also make nice class demonstrations. 6. The hydrophobic and hydrophilic ends of a phospholipid molecule create a lipid bilayer. The hydrophobic edges of the layer will also seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water. Furthermore, because of these hydrophobic properties, lipid bilayers are naturally self-healing. All of these properties emerge from the structure of phospholipid. Active Lecture Tips 1. Consider demonstrating simple diffusion. A large jar of water and a few drops of dark-colored dye work well over the course of a lecture period. Alternatively, release a strong scent of cologne or peppermint or peel part of an orange in the classroom and have students raise their hands as they first detect the smell. Students nearest the source will raise their hands before students farther away. A fan from a projector or overhead vent may bias the experiment a bit, so be aware of any directed movements of air in your classroom that might disrupt this demonstration. 2. See the Activity Using Food and Drink to Describe Osmosis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. Students carefully considering exocytosis may notice that membrane from secretory vesicles is added to the plasma membrane. Challenge your students to work with someone sitting nearby to identify mechanisms that balance out this enlargement of the cell surface. (Endocytosis “subtracts” area from the cell surface. It is a major factor balancing out the additional membrane supplied by exocytosis.) 50

The behavior of animal and plant cells in different osmotic environments
Animal cell H2O H2O H2O H2O Normal Lysing Shriveled Plant cell Plasma membrane H2O H2O H2O H2O Flaccid (wilts) Turgid (normal) Shriveled (a) Isotonic solution (b) Hypotonic solution (c) Hypertonic solution Figure 5.14 Figure 5.14 Osmotic environments

Water Balance in Plant Cells
As a plant cell loses water, it shrivels and its plasma membrane may pull away from the cell wall in the process of plasmolysis, which usually kills the cell. Figure 5.15 Plant turgor

Active Transport: The Pumping of Molecules across Membranes
Active transport requires that a cell expend energy to move molecules across a membrane. Cellular energy (usually provided by ATP) is used to drive a transport protein that pumps a solute against the concentration gradient. Active transport allows cells to maintain internal concentrations of small solutes that differ from environmental concentrations. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. For students with limited science backgrounds, concepts such as diffusion and osmosis can take considerable time to fully understand and apply. Instructors often struggle to remember a time in their lives when they did not know about such fundamental scientific principles. Consider spending extra time to illustrate and demonstrate these key processes to the class. Consider short interactive class exercises in which students create analogies or think of examples of these principles in their lives. 2. Students easily confuse the terms hypertonic and hypotonic. One challenge is to understand that these are relative terms, such as heavier, darker, or fewer. No single solution is “heavier,” no single cup of coffee is “darker,” and no single bag of M & M’s has “fewer” candies. Such terms only apply when comparing two or more items. A solution with a higher concentration is “hypertonic.” But the same solution might also be “hypotonic” to a third solution. Teaching Tips 1. Students often benefit from reminders of diffusion in their lives. Smells can usually be traced back to their sources—the smell of dinner on the stove, the scent of a perfume or cologne coming from its bottle, the smoke drifting away from a campfire. These scents are strongest nearest the source and weaker as we move away. 2. The word root “hypo” means “below.” Thus, a hypodermic needle injects substances below the dermis. Students might best remember that hypotonic solutions have concentrations below that of the other solution(s). 3. After introducing the idea of hypertonic and hypotonic solutions, you may wish to challenge your students with the following: A marine salmon moves from the ocean up a freshwater stream to reproduce. The salmon is moving from a _____ environment to a _____ environment. (Answers: hypertonic; hypotonic) 4. Your students may have noticed that their fingers wrinkle after taking a long shower or bath or washing dishes. The skin wrinkles because it is swollen with water but still tacked down at some points. Oils inhibit the movement of water into our skin. Thus, soapy water results in wrinkling faster than plain water since the soap removes the natural layer of oil from our skin. Our skin is hypertonic to the solutions that produce the swelling that appears as large wrinkles. 5. The effects of hypertonic and hypotonic solutions are easily demonstrated if students soak carrot sticks, long slices of potato, or celery in hypertonic and hypotonic solutions. These also make nice class demonstrations. 6. The hydrophobic and hydrophilic ends of a phospholipid molecule create a lipid bilayer. The hydrophobic edges of the layer will also seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water. Furthermore, because of these hydrophobic properties, lipid bilayers are naturally self-healing. All of these properties emerge from the structure of phospholipid. Active Lecture Tips 1. Consider demonstrating simple diffusion. A large jar of water and a few drops of dark-colored dye work well over the course of a lecture period. Alternatively, release a strong scent of cologne or peppermint or peel part of an orange in the classroom and have students raise their hands as they first detect the smell. Students nearest the source will raise their hands before students farther away. A fan from a projector or overhead vent may bias the experiment a bit, so be aware of any directed movements of air in your classroom that might disrupt this demonstration. 2. See the Activity Using Food and Drink to Describe Osmosis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. Students carefully considering exocytosis may notice that membrane from secretory vesicles is added to the plasma membrane. Challenge your students to work with someone sitting nearby to identify mechanisms that balance out this enlargement of the cell surface. (Endocytosis “subtracts” area from the cell surface. It is a major factor balancing out the additional membrane supplied by exocytosis.) 54

Animation: Active Transport

Active transport Lower solute concentration Solute ATP
Figure 5.16-s2 Lower solute concentration Solute ATP Higher solute concentration Active transport Figure 5.16-s2 Active transport (step 2)

(requires no energy, down the concentration gradient,
MEMBRANE TRANSPORT Passive Transport (requires no energy, down the concentration gradient, movement of molecules from high to tow) Active Transport (requires energy, up against the gradient) Diffusion Facilitated diffusion Osmosis Higher solute concentration Higher water concentration (lower solute concentration) Higher solute concentration Solute Solute Solute Water Solute ATP Lower solute concentration Lower water concentration (higher solute concentration) Lower solute concentration Figure UN3 Summary: membrane transport

Getting through cell membrane
Passive Transport Simple diffusion diffusion of nonpolar, hydrophobic molecules (lipids) HIGH  LOW concentration gradient Facilitated transport diffusion of polar, hydrophilic molecules through a protein channel Active transport diffusion against concentration gradient LOW  HIGH uses a protein pump requires ATP ATP

Exocytosis and Endocytosis: Traffic of Large Molecules
Exocytosis is the secretion of large molecules within vesicles. It happens when secretory proteins exit the cell from transport vesicles that fuse with the plasma membrane, spilling the contents outside the cell. Outside of cell Cytoplasm Plasma membrane The movement of larger molecules into and out of the cell depends on the ability of the membrane to form sacs, thereby packaging the larger moleucules into sacs.

Animation: Exocytosis and Endocytosis Introduction

Endocytosis is when cell takes material into a cell within vesicles that bud inward from the plasma membrane. So it "gulps" particle and packages it with a food vacuole.

Evolution Connection: The Origin of Membranes
Phospholipids are key ingredients of membranes, were probably among the first organic compounds that formed from chemical reactions on early Earth, and self-assemble into simple membranes. © 2013 Pearson Education, Inc. 62

There are three types of endocytosis: Phagocytosis (“cellular eating”); a cell engulfs a particle and packages it within a food vacuole Pinocytosis (“cellular drinking”); a cell “gulps” droplets of fluid by forming tiny vesicles Receptor-mediated endocytosis; a cell takes in very specific molecules

Animation: Phagocytosis

Animation: Pinocytosis

Animation: Receptor-Mediated Endocytosis

Summary: exocytosis and endocytosis
Figure UN4 Summary: exocytosis and endocytosis

Practice Seawater is dangerous to drink because __________. ( Membrane Function) seawater is isotonic to your body fluids and you will absorb too much water, causing your cells to burst one cup of seawater contains enough sodium to poison you the salt causes hypertension and you will promptly die of a stroke seawater is hypertonic to your body tissues and drinking it will cause you to lose water by osmosis it contains toxic levels of iodine

Practice If a red blood cell is placed in an isotonic solution,
water moves into and out of the cell at an equal rate. the cell will swell and then return to normal. the cell will shrivel the cell will swell and burst the cell will shrivel and then return to normal.

Practice Crystals of dye, when placed in a beaker of water, eventually spread evenly throughout the water. This is an example of ______. Lipid-soluble molecules and gases enter the cell by ______. A) diffusion through the channel proteins B) osmosis through the channel proteins C) diffusion through the lipid bilayer D) osmosis through the lipid bilayer E) active transport through the lipid bilayer The diffusion of water across a differentially permeable membrane is called ______.

Practice If two solutions have unequal concentrations of a solute, the solution with the lower concentration is called 1. hypotonic. 2. osmosis. 3. hypnotic. 4. isotonic. 5. hypertonic.

Practice Which type of solution will cause cells to swell, or even to burst? Which type of solution has a lower percentage of solute than the cell? Which of the following processes uses a carrier protein and ATP? A) simple diffusion B) osmosis C) facilitated diffusion D) active transport E) endocytosis Which of the following comparisons is NOT correct? A) endocytosis--entering by sac B) exocytosis--leaving by sac C) active transport--against the gradient D) facilitated diffusion--with the gradient E) hypotonic solution--cells shrivel

Practice An animal cell excretes a protein outside its membrane by the formation of a vesicle. Which process is involved in this transport? 1. endocytosis 2. osmosis 3. passive transport 4. exocytosis 5. phagocytosis

Practice The diffusion of water across a selectively permeable membrane is called _____. ( Membrane Function) a. active transport b. osmosis c. exocytosis d. passive transport e. facilitated diffusion A plant cell placed in a hypotonic solution will not lyse because _____. ( Membrane Function) a. the cell wall prevents the plant cell from bursting b. it becomes turgid c. it shrivels d. plant plasma membranes are impermeable to water e. it is flaccid

Practice Some liver cells ingest bacteria, a function probably accomplished by _____. ( Membrane Function) a. pinocytosis b. phagocytosis c. receptor-mediated d. endocytosis e. exocytosis f. passive transport The secretion of neurotransmitters out of the nerve cell, from small vesicles at the end of the axon, can be considered an example of _____. ( Membrane Function)

Which beaker(s) contain(s) a solution that is hypertonic to the bag?
a. Which beaker(s) contain(s) a solution that is hypertonic to the bag? b. Which beaker(s) contain(s) a solution that is hypertonic to the bag? c. isotonic?

Practice Which one of the following is involved in facilitated diffusion? ( Membrane Function) Osmosis a concentration gradient an outside energy source a pump a nucleic acid

Practice Which of the following is a difference between active transport and facilitated diffusion? ( Membrane Function) Facilitated diffusion requires energy from ATP, and active transport does not. Active transport requires the expenditure of cellular energy, and facilitated diffusion does not. Facilitated diffusion can move solutes against a concentration gradient, and active transport cannot. Facilitated diffusion involves transport proteins, and active transport does not. Active transport involves transport proteins, and facilitated diffusion does not.

Practice Which of the following is NOT an active method where molecules pass across the plasma membrane? simple diffusion active transport Endocytosis exocytosis The plasma membrane, because of the channel proteins, is said to be freely permeable. A) True B) False Macromolecules can freely cross a plasma membrane.

Practice A nursing infant is able to obtain disease-fighting antibodies, which are large protein molecules, from its mother's milk. These molecules probably enter the cells lining the baby's digestive tract via _____. ( Membrane Function) Osmosis active transport Endocytosis Exocytosis passive transport

Practice The secretion of neurotransmitters out of the nerve cell, from small vesicles at the end of the axon, can be considered an example of _____. ( Membrane Function) Pinocytosis Exocytosis Endocytosis Osmoregulation phagocytosis

Practice Identify the energy needs of simple diffusion, osmosis, facilitated diffusion, active transport/solute pumping, endocytosis, and exocytosis. What type of transport uses protein carriers driven by the expenditure of chemical energy to move solute across a membrane against its concentration gradient? Osmosis active transport Exocytosis Diffusion facilitated transport

Phospholipids are key ingredients of membranes, were probably among the first organic compounds that formed from chemical reactions on early Earth, and self-assemble into simple membranes. The tendency of lipids in water to spontaneously form membranes has led biomedical engineers to produce liposomes (a type of artificial vesicle) that can encase particular chemicals. These engineered liposomes may be used to deliver nutrients or medications to specific sites within the body. Student Misconceptions and Concerns 1. For students with limited science backgrounds, concepts such as diffusion and osmosis can take considerable time to fully understand and apply. Instructors often struggle to remember a time in their lives when they did not know about such fundamental scientific principles. Consider spending extra time to illustrate and demonstrate these key processes to the class. Consider short interactive class exercises in which students create analogies or think of examples of these principles in their lives. 2. Students easily confuse the terms hypertonic and hypotonic. One challenge is to understand that these are relative terms, such as heavier, darker, or fewer. No single solution is “heavier,” no single cup of coffee is “darker,” and no single bag of M & M’s has “fewer” candies. Such terms only apply when comparing two or more items. A solution with a higher concentration is “hypertonic.” But the same solution might also be “hypotonic” to a third solution. Teaching Tips 1. Students often benefit from reminders of diffusion in their lives. Smells can usually be traced back to their sources—the smell of dinner on the stove, the scent of a perfume or cologne coming from its bottle, the smoke drifting away from a campfire. These scents are strongest nearest the source and weaker as we move away. 2. The word root “hypo” means “below.” Thus, a hypodermic needle injects substances below the dermis. Students might best remember that hypotonic solutions have concentrations below that of the other solution(s). 3. After introducing the idea of hypertonic and hypotonic solutions, you may wish to challenge your students with the following: A marine salmon moves from the ocean up a freshwater stream to reproduce. The salmon is moving from a _____ environment to a _____ environment. (Answers: hypertonic; hypotonic) 4. Your students may have noticed that their fingers wrinkle after taking a long shower or bath or washing dishes. The skin wrinkles because it is swollen with water but still tacked down at some points. Oils inhibit the movement of water into our skin. Thus, soapy water results in wrinkling faster than plain water since the soap removes the natural layer of oil from our skin. Our skin is hypertonic to the solutions that produce the swelling that appears as large wrinkles. 5. The effects of hypertonic and hypotonic solutions are easily demonstrated if students soak carrot sticks, long slices of potato, or celery in hypertonic and hypotonic solutions. These also make nice class demonstrations. 6. The hydrophobic and hydrophilic ends of a phospholipid molecule create a lipid bilayer. The hydrophobic edges of the layer will also seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water. Furthermore, because of these hydrophobic properties, lipid bilayers are naturally self-healing. All of these properties emerge from the structure of phospholipid. Active Lecture Tips 1. Consider demonstrating simple diffusion. A large jar of water and a few drops of dark-colored dye work well over the course of a lecture period. Alternatively, release a strong scent of cologne or peppermint or peel part of an orange in the classroom and have students raise their hands as they first detect the smell. Students nearest the source will raise their hands before students farther away. A fan from a projector or overhead vent may bias the experiment a bit, so be aware of any directed movements of air in your classroom that might disrupt this demonstration. 2. See the Activity Using Food and Drink to Describe Osmosis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. Students carefully considering exocytosis may notice that membrane from secretory vesicles is added to the plasma membrane. Challenge your students to work with someone sitting nearby to identify mechanisms that balance out this enlargement of the cell surface. (Endocytosis “subtracts” area from the cell surface. It is a major factor balancing out the additional membrane supplied by exocytosis.) 83

The spontaneous formation of membranes: a key step in the origin of life
Water-filled bubble made of phospholipids Colorized LM Figure 5.19 Figure 5.19 The spontaneous formation of membranes: a key step in the origin of life

The formation of membrane-enclosed collections of molecules would have been a critical step in the evolution of the first cells. A membrane can enclose a solution that is different in composition from its surroundings. A plasma membrane that allows cells to regulate their chemical exchanges with the environment is a basic requirement for life. Indeed, all cells are enclosed by a plasma membrane that is similar in structure and function— illustrating the evolutionary unity of life. Student Misconceptions and Concerns 1. For students with limited science backgrounds, concepts such as diffusion and osmosis can take considerable time to fully understand and apply. Instructors often struggle to remember a time in their lives when they did not know about such fundamental scientific principles. Consider spending extra time to illustrate and demonstrate these key processes to the class. Consider short interactive class exercises in which students create analogies or think of examples of these principles in their lives. 2. Students easily confuse the terms hypertonic and hypotonic. One challenge is to understand that these are relative terms, such as heavier, darker, or fewer. No single solution is “heavier,” no single cup of coffee is “darker,” and no single bag of M & M’s has “fewer” candies. Such terms only apply when comparing two or more items. A solution with a higher concentration is “hypertonic.” But the same solution might also be “hypotonic” to a third solution. Teaching Tips 1. Students often benefit from reminders of diffusion in their lives. Smells can usually be traced back to their sources—the smell of dinner on the stove, the scent of a perfume or cologne coming from its bottle, the smoke drifting away from a campfire. These scents are strongest nearest the source and weaker as we move away. 2. The word root “hypo” means “below.” Thus, a hypodermic needle injects substances below the dermis. Students might best remember that hypotonic solutions have concentrations below that of the other solution(s). 3. After introducing the idea of hypertonic and hypotonic solutions, you may wish to challenge your students with the following: A marine salmon moves from the ocean up a freshwater stream to reproduce. The salmon is moving from a _____ environment to a _____ environment. (Answers: hypertonic; hypotonic) 4. Your students may have noticed that their fingers wrinkle after taking a long shower or bath or washing dishes. The skin wrinkles because it is swollen with water but still tacked down at some points. Oils inhibit the movement of water into our skin. Thus, soapy water results in wrinkling faster than plain water since the soap removes the natural layer of oil from our skin. Our skin is hypertonic to the solutions that produce the swelling that appears as large wrinkles. 5. The effects of hypertonic and hypotonic solutions are easily demonstrated if students soak carrot sticks, long slices of potato, or celery in hypertonic and hypotonic solutions. These also make nice class demonstrations. 6. The hydrophobic and hydrophilic ends of a phospholipid molecule create a lipid bilayer. The hydrophobic edges of the layer will also seal to other such edges, eventually wrapping a sheet into a sphere that can enclose water. Furthermore, because of these hydrophobic properties, lipid bilayers are naturally self-healing. All of these properties emerge from the structure of phospholipid. Active Lecture Tips 1. Consider demonstrating simple diffusion. A large jar of water and a few drops of dark-colored dye work well over the course of a lecture period. Alternatively, release a strong scent of cologne or peppermint or peel part of an orange in the classroom and have students raise their hands as they first detect the smell. Students nearest the source will raise their hands before students farther away. A fan from a projector or overhead vent may bias the experiment a bit, so be aware of any directed movements of air in your classroom that might disrupt this demonstration. 2. See the Activity Using Food and Drink to Describe Osmosis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. Students carefully considering exocytosis may notice that membrane from secretory vesicles is added to the plasma membrane. Challenge your students to work with someone sitting nearby to identify mechanisms that balance out this enlargement of the cell surface. (Endocytosis “subtracts” area from the cell surface. It is a major factor balancing out the additional membrane supplied by exocytosis.) 85

The Process of Science: Can Enzymes Be Engineered?
Observation: Genetic sequences suggest that many of our genes were formed through a type of molecular evolution. Question: Can laboratory methods mimic this process through artificial selection? Hypothesis: An artificial process could be used to modify the gene that codes for lactase into a new gene coding for an enzyme with a new function. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. For students not previously familiar with activation energy, analogies can make all the difference. Activation energy can be thought of as a small input that is needed to trigger a large output. This is like (a) an irritated person who needs only a bit more frustration to explode in anger, (b) small waves that lift debris over a dam, or (c) lighting a match around lighter fluid. In each situation, the output was much greater than the input. 2. The specific interactions of enzymes and substrates can be illustrated with simple physical models. Many students new to these concepts will benefit from several forms of explanation, including diagrams such as those in the textbook, physical models, and the opportunity to manipulate or create their own examples. New concepts, like pitching a tent, are best constructed with many lines of support. Teaching Tips 1. The text notes that the relationship between an enzyme and its substrate is like a handshake, with each hand generally conforming to the shape of the other. This induced fit is also like the change in shape of a glove when a hand is inserted. The glove’s general shape matches the hand, but the final “fit” requires some additional adjustments. 2. Enzyme inhibitors that block the active site are like (a) a person sitting in your assigned theater seat or (b) a car parked in your parking space. Analogies for inhibitors that change the shape of the active site are more difficult to imagine. Consider challenging your students to think of such analogies. (Perhaps someone adjusting the driver seat of the car differently from your preferences and then leaving it that way when you try to use the car.) 3. Consider challenging your class to suggest advantages to using specific enzyme inhibitors as insect poisons. Many advantages exist and include (a) the ability to target chemical reactions of only certain types of pest organisms and (b) the ability to target chemical reactions that are found in insects but not in humans. 4. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. Yet in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might be curious, and you could point out that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, which are proteins with the ability to control the production of carbohydrates and lipids. Active Lecture Tips 1. Feedback regulation relies on the negative feedback of the accumulation of a product. Ask students in class to work in pairs to suggest other products of reactions that inhibit the process that made them, when the product reaches high enough levels. (Gas station pumps routinely shut off when a high level of gasoline is detected. Furnaces typically turn off when enough heat has been produced, and toilets stop running when the tank is refilled.) 2. See the Activity Students, Design Your Own Enzyme-Catalyzed Reaction on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. See the Activity Lock and Key Analogy with Enzymes on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 86

The Process of Science: Can Enzymes Be Engineered?
Experiment: Using the process of directed evolution, many copies of the lactase gene were randomly mutated and tested for new activities. Results: Directed evolution produced a new enzyme with a novel function. © 2016 Pearson Education, Inc. Student Misconceptions and Concerns 1. For students not previously familiar with activation energy, analogies can make all the difference. Activation energy can be thought of as a small input that is needed to trigger a large output. This is like (a) an irritated person who needs only a bit more frustration to explode in anger, (b) small waves that lift debris over a dam, or (c) lighting a match around lighter fluid. In each situation, the output was much greater than the input. 2. The specific interactions of enzymes and substrates can be illustrated with simple physical models. Many students new to these concepts will benefit from several forms of explanation, including diagrams such as those in the textbook, physical models, and the opportunity to manipulate or create their own examples. New concepts, like pitching a tent, are best constructed with many lines of support. Teaching Tips 1. The text notes that the relationship between an enzyme and its substrate is like a handshake, with each hand generally conforming to the shape of the other. This induced fit is also like the change in shape of a glove when a hand is inserted. The glove’s general shape matches the hand, but the final “fit” requires some additional adjustments. 2. Enzyme inhibitors that block the active site are like (a) a person sitting in your assigned theater seat or (b) a car parked in your parking space. Analogies for inhibitors that change the shape of the active site are more difficult to imagine. Consider challenging your students to think of such analogies. (Perhaps someone adjusting the driver seat of the car differently from your preferences and then leaving it that way when you try to use the car.) 3. Consider challenging your class to suggest advantages to using specific enzyme inhibitors as insect poisons. Many advantages exist and include (a) the ability to target chemical reactions of only certain types of pest organisms and (b) the ability to target chemical reactions that are found in insects but not in humans. 4. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. Yet in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might be curious, and you could point out that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, which are proteins with the ability to control the production of carbohydrates and lipids. Active Lecture Tips 1. Feedback regulation relies on the negative feedback of the accumulation of a product. Ask students in class to work in pairs to suggest other products of reactions that inhibit the process that made them, when the product reaches high enough levels. (Gas station pumps routinely shut off when a high level of gasoline is detected. Furnaces typically turn off when enough heat has been produced, and toilets stop running when the tank is refilled.) 2. See the Activity Students, Design Your Own Enzyme-Catalyzed Reaction on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 3. See the Activity Lock and Key Analogy with Enzymes on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. 87

(mutations shown in orange)
Figure 5.8 Gene for lactase Gene duplicated and mutated at random Mutated genes (mutations shown in orange) Mutated genes screened by testing new enzymes Genes coding for enzymes that show new activity Genes coding for enzymes that do not show new activity Computer-generated model of the enzyme lactase Genes duplicated and mutated at random Mutated genes screened by testing new enzymes After seven rounds, some genes code for enzymes that can efficiently perform new activity. Figure 5.8 Directed evolution of an enzyme

(mutations shown in orange)
Figure 5.8-1 Gene for lactase Gene duplicated and mutated at random Mutated genes (mutations shown in orange) Figure Directed evolution of an enzyme (part 1: lactase)

Mutated genes screened by testing new enzymes
Figure 5.8-2 Mutated genes screened by testing new enzymes Genes coding for enzymes that show new activity Genes coding for enzymes that do not show new activity Genes duplicated and mutated at random After seven rounds, some genes code for enzymes that can efficiently perform new activity. Mutated genes screened by testing new enzymes Figure Directed evolution of an enzyme (part 2: mutated genes)

Computer-generated model of the enzyme lactase
Figure 5.8-3 Computer-generated model of the enzyme lactase Figure Directed evolution of an enzyme (part 3: computer-generated model of lactase)

Chapter 5 The Working Cell © 2016 Pearson Education, Inc.

Similar presentations

Presentation on theme: "Chapter 5 The Working Cell © 2016 Pearson Education, Inc."— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Chapter 5 The Working Cell © 2016 Pearson Education, Inc.

Similar presentations

Presentation on theme: "Chapter 5 The Working Cell © 2016 Pearson Education, Inc."— Presentation transcript:

Similar presentations

About project

Feedback