Chapter 5 The Working Cell.

Chapter 5 The Working Cell

Membrane Structure and Function
Figure 5.0_1 Chapter 5: Big Ideas Cellular respiration Membrane Structure and Function Energy and the Cell Figure 5.0_1 Chapter 5: Big Ideas How Enzymes Function 2

Introduction Many of a cell’s reactions
take place in organelles and use enzymes embedded in the membranes of these organelles. This chapter addresses how working cells use membranes, energy, and enzymes. © 2012 Pearson Education, Inc. 3

MEMBRANE STRUCTURE AND FUNCTION
© 2012 Pearson Education, Inc. 4

5.1 Membranes are fluid mosaics of lipids and proteins with many functions
Membranes are composed of a bilayer of phospholipids with embedded and attached proteins, in a structure biologists call a fluid mosaic. Teaching Tips You might wish to share a very simple analogy that seems to work well for some students. A cell membrane is a little like a peanut butter and jelly sandwich with jellybeans poked into it. The bread represents the hydrophilic portions of the bilayer (and bread does indeed quickly absorb water). The peanut butter and jelly represent the hydrophobic regions (and peanut butter, containing plenty of oil, is generally hydrophobic). The jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans that poke completely through the sandwich. Analogies are rarely perfect. Challenge your students to critique this analogy by finding exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.) © 2012 Pearson Education, Inc. 5

Many phospholipids are made from unsaturated fatty acids that have kinks in their tails. These kinks prevent phospholipids from packing tightly together, keeping them in liquid form. In animal cell membranes, cholesterol helps stabilize membranes at warmer temperatures and keep the membrane fluid at lower temperatures. Teaching Tips You might wish to share a very simple analogy that seems to work well for some students. A cell membrane is a little like a peanut butter and jelly sandwich with jellybeans poked into it. The bread represents the hydrophilic portions of the bilayer (and bread does indeed quickly absorb water). The peanut butter and jelly represent the hydrophobic regions (and peanut butter, containing plenty of oil, is generally hydrophobic). The jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans that poke completely through the sandwich. Analogies are rarely perfect. Challenge your students to critique this analogy by finding exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.) © 2012 Pearson Education, Inc. 6

Fibers of extracellular matrix (ECM)
Figure 5.1 CYTOPLASM Enzymatic activity Fibers of extracellular matrix (ECM) Phospholipid Cell-cell recognition Cholesterol Receptor Signaling molecule Figure 5.1 Some functions of membrane proteins Intercellular junctions ATP Transport Glycoprotein Signal transduction Attachment to the cytoskeleton and extracellular matrix (ECM) Microfilaments of cytoskeleton CYTOPLASM 7

Membrane proteins perform many functions. Some proteins help maintain cell shape and coordinate changes inside and outside the cell through their attachment to the cytoskeleton and extracellular matrix. Some proteins function as receptors for chemical messengers from other cells. Some membrane proteins function as enzymes. Teaching Tips You might wish to share a very simple analogy that seems to work well for some students. A cell membrane is a little like a peanut butter and jelly sandwich with jellybeans poked into it. The bread represents the hydrophilic portions of the bilayer (and bread does indeed quickly absorb water). The peanut butter and jelly represent the hydrophobic regions (and peanut butter, containing plenty of oil, is generally hydrophobic). The jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans that poke completely through the sandwich. Analogies are rarely perfect. Challenge your students to critique this analogy by finding exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.) © 2012 Pearson Education, Inc. 8

Some membrane glycoproteins are involved in cell-cell recognition. Membrane proteins may participate in the intercellular junctions that attach adjacent cells to each other. Membranes may exhibit selective permeability, allowing some substances to cross more easily than others. Teaching Tips You might wish to share a very simple analogy that seems to work well for some students. A cell membrane is a little like a peanut butter and jelly sandwich with jellybeans poked into it. The bread represents the hydrophilic portions of the bilayer (and bread does indeed quickly absorb water). The peanut butter and jelly represent the hydrophobic regions (and peanut butter, containing plenty of oil, is generally hydrophobic). The jellybeans stuck into the sandwich represent proteins variously embedded partially into or completely through the membrane. Transport proteins would be like the jellybeans that poke completely through the sandwich. Analogies are rarely perfect. Challenge your students to critique this analogy by finding exceptions. (For example, this analogy does not include a model of the carbohydrates on the cell surface.) Animation: Signal Transduction Pathways Animation: Overview of Cell Signaling © 2012 Pearson Education, Inc. 9

5.2 Membranes form spontaneously
Phospholipids, the key ingredient of biological membranes, spontaneously self-assemble into simple membranes. Teaching Tips 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 phospholipids. © 2012 Pearson Education, Inc. 10

Water-filled bubble made of phospholipids
Figure 5.2 Figure 5.2 Artificial membrane-bounded sacs Water-filled bubble made of phospholipids 11

Figure 5.2Q Water Figure 5.2Q Structure of membrane sacs Water 12

5.3 Passive transport is diffusion across a membrane with no energy investment
Diffusion is the tendency of particles to spread out evenly in an available space. Particles move from an area of more concentrated particles to an area where they are less concentrated. This means that particles diffuse down their concentration gradient. Eventually, the particles reach equilibrium where the concentration of particles is the same throughout. Student Misconceptions and Concerns 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. 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 perfume or cologne from a bottle, the smoke drifting away from a campfire. These scents are strongest nearest the source and weaker as we move away. 2. 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. The fan from an active overhead 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. © 2012 Pearson Education, Inc. 13

Animation: Membrane Selectivity
5.3 Passive transport is diffusion across a membrane with no energy investment Diffusion across a cell membrane does not require energy, so it is called passive transport. The concentration gradient itself represents potential energy for diffusion. Example: Oxygen and Carbon dioxide. Both small, nonpolar molecules. Student Misconceptions and Concerns 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. 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 perfume or cologne from a bottle, the smoke drifting away from a campfire. These scents are strongest nearest the source and weaker as we move away. 2. 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. The fan from an active overhead 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. Animation: Diffusion Animation: Membrane Selectivity © 2012 Pearson Education, Inc. 14

Molecules of dye Membrane Pores Net diffusion Net diffusion
Figure 5.3A Molecules of dye Membrane Pores Figure 5.3A Passive transport of one type of molecule Net diffusion Net diffusion Equilibrium 15

Net diffusion Net diffusion Equilibrium Net diffusion Net diffusion
Figure 5.3B Net diffusion Net diffusion Equilibrium Figure 5.3B Passive transport of two types of molecules Net diffusion Net diffusion Equilibrium 16

5.4 Osmosis is the diffusion of water across a membrane
One of the most important substances that crosses membranes is water. The diffusion of water across a selectively permeable membrane is called osmosis. Student Misconceptions and Concerns 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. Teaching Tips Your students may have noticed that the skin of their fingers wrinkles after taking a long shower or bath, or after washing dishes. The skin wrinkles because it is swollen with water but still tacked down at some points. Through osmosis, water moves into the epidermal skin cells. Our skin is hypertonic to these solutions, producing the swelling that appears as large wrinkles. Oils inhibit the movement of water into our skin. Thus, soapy water results in wrinkling faster than plain water because the soap removes the natural layer of oil from our skin. Animation: Osmosis © 2012 Pearson Education, Inc. 17

5.4 Osmosis is the diffusion of water across a membrane
If a membrane permeable to water but not a solute separates two solutions with different concentrations of solute, water will cross the membrane, moving down its own concentration gradient, until the solute concentration on both sides is equal. Student Misconceptions and Concerns 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. Teaching Tips Your students may have noticed that the skin of their fingers wrinkles after taking a long shower or bath, or after washing dishes. The skin wrinkles because it is swollen with water but still tacked down at some points. Through osmosis, water moves into the epidermal skin cells. Our skin is hypertonic to these solutions, producing the swelling that appears as large wrinkles. Oils inhibit the movement of water into our skin. Thus, soapy water results in wrinkling faster than plain water because the soap removes the natural layer of oil from our skin. © 2012 Pearson Education, Inc. 18

Lower concentration of solute Higher concentration of solute
Figure 5.4 Lower concentration of solute Higher concentration of solute Equal concentrations of solute H2O Solute molecule Selectively permeable membrane Water molecule Figure 5.4 Osmosis, the diffusion of water across a membrane Solute molecule with cluster of water molecules Osmosis 19

5.5 Water balance between cells and their surroundings is crucial to organisms
Tonicity is a term that describes the ability of a solution to cause a cell to gain or lose water. Tonicity mostly depends on the concentration of a solute on both sides of the membrane. Student Misconceptions and Concerns Students easily confuse the term hypertonic and hypotonic. One challenge is to get them to understand that these are relative terms, such as heavier, darker, or fewer. No single object 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 than another solution is hypertonic to that solution. However, the same solution might also be hypotonic to a third solution. Teaching Tips 1. The word root hypo means “below.” Thus, a hypodermic needle injects substances below the dermis. Students might best remember that hypotonic solutions have concentrations of solutes below that of the other solution(s). 2. After introducing the idea of hypertonic and hypotonic solutions, you may wish to challenge your students with the following: A salmon might swim from the ocean up a freshwater stream to reproduce. The salmon is moving from a _____ environment to a _____ environment. (Answers: hypertonic, hypotonic) 3. The effects of hypertonic and hypotonic solutions can be demonstrated if students soak carrot sticks, long slices of potato, or celery in hypertonic and hypotonic solutions. These also make nice class demonstrations. © 2012 Pearson Education, Inc. 20

How will animal cells be affected when placed into solutions of various tonicities? When an animal cell is placed into an isotonic solution, the concentration of solute is the same on both sides of a membrane, and the cell volume will not change, a hypotonic solution, the solute concentration is lower outside the cell, water molecules move into the cell, and the cell will expand and may burst, or a hypertonic solution, the solute concentration is higher outside the cell, water molecules move out of the cell, and the cell will shrink. Student Misconceptions and Concerns Students easily confuse the term hypertonic and hypotonic. One challenge is to get them to understand that these are relative terms, such as heavier, darker, or fewer. No single object 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 than another solution is hypertonic to that solution. However, the same solution might also be hypotonic to a third solution. Teaching Tips 1. The word root hypo means “below.” Thus, a hypodermic needle injects substances below the dermis. Students might best remember that hypotonic solutions have concentrations of solutes below that of the other solution(s). 2. After introducing the idea of hypertonic and hypotonic solutions, you may wish to challenge your students with the following: A salmon might swim from the ocean up a freshwater stream to reproduce. The salmon is moving from a _____ environment to a _____ environment. (Answers: hypertonic, hypotonic) 3. The effects of hypertonic and hypotonic solutions can be demonstrated if students soak carrot sticks, long slices of potato, or celery in hypertonic and hypotonic solutions. These also make nice class demonstrations. © 2012 Pearson Education, Inc. 21

For an animal cell to survive in a hypotonic or hypertonic environment, it must engage in osmoregulation, the control of water balance. Student Misconceptions and Concerns Students easily confuse the term hypertonic and hypotonic. One challenge is to get them to understand that these are relative terms, such as heavier, darker, or fewer. No single object 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 than another solution is hypertonic to that solution. However, the same solution might also be hypotonic to a third solution. Teaching Tips 1. The word root hypo means “below.” Thus, a hypodermic needle injects substances below the dermis. Students might best remember that hypotonic solutions have concentrations of solutes below that of the other solution(s). 2. After introducing the idea of hypertonic and hypotonic solutions, you may wish to challenge your students with the following: A salmon might swim from the ocean up a freshwater stream to reproduce. The salmon is moving from a _____ environment to a _____ environment. (Answers: hypertonic, hypotonic) 3. The effects of hypertonic and hypotonic solutions can be demonstrated if students soak carrot sticks, long slices of potato, or celery in hypertonic and hypotonic solutions. These also make nice class demonstrations. © 2012 Pearson Education, Inc. 22

Video: Paramecium Vacuole
5.5 Water balance between cells and their surroundings is crucial to organisms The cell walls of plant cells, prokaryotes, and fungi make water balance issues somewhat different. The cell wall of a plant cell exerts pressure that prevents the cell from taking in too much water and bursting when placed in a hypotonic environment. But in a hypertonic environment, plant and animal cells both shrivel. Student Misconceptions and Concerns Students easily confuse the term hypertonic and hypotonic. One challenge is to get them to understand that these are relative terms, such as heavier, darker, or fewer. No single object 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 than another solution is hypertonic to that solution. However, the same solution might also be hypotonic to a third solution. Teaching Tips 1. The word root hypo means “below.” Thus, a hypodermic needle injects substances below the dermis. Students might best remember that hypotonic solutions have concentrations of solutes below that of the other solution(s). 2. After introducing the idea of hypertonic and hypotonic solutions, you may wish to challenge your students with the following: A salmon might swim from the ocean up a freshwater stream to reproduce. The salmon is moving from a _____ environment to a _____ environment. (Answers: hypertonic, hypotonic) 3. The effects of hypertonic and hypotonic solutions can be demonstrated if students soak carrot sticks, long slices of potato, or celery in hypertonic and hypotonic solutions. These also make nice class demonstrations. Video: Chlamydomonas Video: Plasmolysis Video: Paramecium Vacuole Video: Turgid Elodea © 2012 Pearson Education, Inc. 23

Shriveled (plasmolyzed)
Figure 5.5 Hypotonic solution Isotonic solution Hypertonic solution H2O H2O H2O H2O Animal cell Lysed Normal Shriveled H2O H2O Plasma membrane H2O Plant cell Figure 5.5 How animal and plant cells react to changes in tonicity Turgid (normal) Flaccid Shriveled (plasmolyzed) 24

5.6 Transport proteins can facilitate diffusion across membranes
Hydrophobic substances easily diffuse across a cell membrane. However, polar or charged substances do not easily cross cell membranes and, instead, move across membranes with the help of specific transport proteins in a process called facilitated diffusion, which does not require energy and relies on the concentration gradient. Teaching Tips The text notes that “The greater the number of transport proteins for a particular solute in a membrane, the faster the solute’s rate of diffusion across the membrane.” This is similar to a situation that might be more familiar to your students. The more ticket-takers present at the entrance to a stadium, the faster the rate of movement of people into the stadium. © 2012 Pearson Education, Inc. 25 25

Some proteins function by becoming a hydrophilic tunnel for passage of ions or other molecules. Other proteins bind their passenger, change shape, and release their passenger on the other side. In both of these situations, the protein is specific for the substrate, which can be sugars, amino acids, ions, and even water. Teaching Tips The text notes that “The greater the number of transport proteins for a particular solute in a membrane, the faster the solute’s rate of diffusion across the membrane.” This is similar to a situation that might be more familiar to your students. The more ticket-takers present at the entrance to a stadium, the faster the rate of movement of people into the stadium. © 2012 Pearson Education, Inc. 26 26

Because water is polar, its diffusion through a membrane’s hydrophobic interior is relatively slow. The very rapid diffusion of water into and out of certain cells is made possible by a protein channel called an aquaporin. Teaching Tips The text notes that “The greater the number of transport proteins for a particular solute in a membrane, the faster the solute’s rate of diffusion across the membrane.” This is similar to a situation that might be more familiar to your students. The more ticket-takers present at the entrance to a stadium, the faster the rate of movement of people into the stadium. © 2012 Pearson Education, Inc. 27 27

Solute molecule Transport protein Figure 5.6
Figure 5.6 Transport protein providing a channel for the diffusion of a specific solute across a membrane Transport protein 28

5.7 SCIENTIFIC DISCOVERY: Research on another membrane protein led to the discovery of aquaporins
Dr. Peter Agre received the 2003 Nobel Prize in chemistry for his discovery of aquaporins. His research on the Rh protein used in blood typing led to this discovery. Teaching Tips The functional significance of aquaporins in cell membranes is somewhat like open windows in a home. Even without windows, air moves slowly into and out of a home. Open windows and aquaporins facilitate the process of these movements, speeding them up. © 2012 Pearson Education, Inc. 29

Figure 5.7 Figure 5.7 Aquaporin in action 30

5.8 Cells expend energy in the active transport of a solute
In active transport, a cell must expend energy to move a solute against its concentration gradient. The following figures show the four main stages of active transport. Teaching Tips 1. Active transport uses energy to move a solute against its concentration gradient. Challenge your students to think of the many possible analogies to this situation, for example, bailing out a leaky boat by moving water back to a place (outside the boat) where water is more concentrated. An alternative analogy might be the herding of animals, which requires work to keep the organisms concentrated and counteract their natural tendency to spread out. 2. Students familiar with city subway toll stations might think of some gate mechanisms that work similarly to the proteins regulating active transport. A person steps up to a barrier and inserts payment (analogous to ATP input), and the gate changes shape, permitting passage to the other side. Even a simple turnstile system that requires payment is generally similar. Animation: Active Transport © 2012 Pearson Education, Inc. 31

Transport protein Solute Solute binding 1 Figure 5.8_s1
Figure 5.8_s1 Active transport of a solute across a membrane (step 1) 1 Solute binding 32

Transport protein P ATP Solute ADP Solute binding Phosphate attaching
Figure 5.8_s2 Transport protein P ATP Solute ADP Figure 5.8_s2 Active transport of a solute across a membrane (step 2) 1 Solute binding 2 Phosphate attaching 33

Transport protein P P Protein changes shape. ATP Solute ADP
Figure 5.8_s3 Transport protein P P Protein changes shape. ATP Solute ADP Figure 5.8_s3 Active transport of a solute across a membrane (step 3) 1 Solute binding 2 Phosphate attaching 3 Transport 34

Transport protein P P Protein changes shape. Phosphate detaches. P ATP
Figure 5.8_s4 Transport protein P P Protein changes shape. Phosphate detaches. P ATP Solute ADP Figure 5.8_s4 Active transport of a solute across a membrane (step 4) 1 Solute binding 2 Phosphate attaching 3 Transport 4 Protein reversion 35

5.9 Exocytosis and endocytosis transport large molecules across membranes
A cell uses two mechanisms to move large molecules across membranes. Exocytosis is used to export bulky molecules, such as proteins or polysaccharides. Endocytosis is used to import substances useful to the livelihood of the cell. In both cases, material to be transported is packaged within a vesicle that fuses with the membrane. Teaching Tips Students carefully considering exocytosis may notice that membrane from secretory vesicles is added to the plasma membrane. Consider challenging your students 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.) © 2012 Pearson Education, Inc. 36

5.9 Exocytosis and endocytosis transport large molecules across membranes
There are three kinds of endocytosis. Phagocytosis is the engulfment of a particle by wrapping cell membrane around it, forming a vacuole. Pinocytosis is the same thing except that fluids are taken into small vesicles. Receptor-mediated endocytosis uses receptors in a receptor-coated pit to interact with a specific protein, initiating the formation of a vesicle. Teaching Tips Students carefully considering exocytosis may notice that membrane from secretory vesicles is added to the plasma membrane. Consider challenging your students 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.) Animation: Exocytosis and Endocytosis Introduction Animation: Exocytosis Animation: Pinocytosis Animation: Phagocytosis Animation: Receptor-Mediated Endocytosis © 2012 Pearson Education, Inc. 37

Figure 5.9 Three kinds of endocytosis
Phagocytosis EXTRACELLULAR FLUID CYTOPLASM Food being ingested Pseudopodium “Food” or other particle Food vacuole Pinocytosis Plasma membrane Vesicle Figure 5.9 Three kinds of endocytosis Plasma membrane Receptor-mediated endocytosis Coat protein Receptor Coated vesicle Coated pit Coated pit Specific molecule Material bound to receptor proteins 38

“Food” or other particle
Figure 5.9_1 Phagocytosis EXTRACELLULAR FLUID CYTOPLASM Food being ingested Pseudopodium “Food” or other particle Figure 5.9_1 Three kinds of endocytosis (part 1) Food vacuole 39

Pinocytosis Plasma membrane Vesicle Plasma membrane Figure 5.9_2
Figure 5.9_2 Three kinds of endocytosis (part 2) Plasma membrane 40

Receptor-mediated endocytosis Coat protein
Figure 5.9_3 Plasma membrane Receptor-mediated endocytosis Coat protein Coated vesicle Receptor Coated pit Coated pit Specific molecule Figure 5.9_3 Three kinds of endocytosis (part 3) Material bound to receptor proteins 41

5.10 Cells transform energy as they perform work
Cells are small units, a chemical factory, housing thousands of chemical reactions. Cells use these chemical reactions for cell maintenance, manufacture of cellular parts, and cell replication. Student Misconceptions and Concerns 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. Teaching Tips 1. 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). Consider challenging your students to come up with additional examples of such common energy conversions in their lives. 2. Some students can relate well to the concept of entropy as applied to the room where they live. Despite their cleaning up and organizing the room on a regular (or irregular) basis, the room becomes increasingly 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.” 3. The heat produced by the engine of a car is typically used to heat the car during cold weather. However, is this same heat available in warmer weather? Students are often unaware that their car “heaters” work 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 weather is warm. 4. Here is a question that might make cellular respiration a little more meaningful to your students. Ask your students 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? The answer is, 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. © 2012 Pearson Education, Inc. 43

Energy is the capacity to cause change or to perform work. There are two kinds of energy. Kinetic energy is the energy of motion. Potential energy is energy that matter possesses as a result of its location or structure. Student Misconceptions and Concerns 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. Teaching Tips 1. 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). Consider challenging your students to come up with additional examples of such common energy conversions in their lives. 2. Some students can relate well to the concept of entropy as applied to the room where they live. Despite their cleaning up and organizing the room on a regular (or irregular) basis, the room becomes increasingly 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.” 3. The heat produced by the engine of a car is typically used to heat the car during cold weather. However, is this same heat available in warmer weather? Students are often unaware that their car “heaters” work 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 weather is warm. 4. Here is a question that might make cellular respiration a little more meaningful to your students. Ask your students 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? The answer is, 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. © 2012 Pearson Education, Inc. 44

Kinetic energy of movement
Figure 5.10 Fuel Energy conversion Waste products Heat energy Carbon dioxide Gasoline   Combustion Kinetic energy of movement Oxygen Water Energy conversion in a car Heat energy Figure 5.10 Energy transformations in a car and a cell Cellular respiration Glucose Carbon dioxide   ATP ATP Oxygen Energy for cellular work Water Energy conversion in a cell 45

Kinetic energy of movement
Figure 5.10_1 Fuel Energy conversion Waste products Heat energy Carbon dioxide Gasoline   Combustion Kinetic energy of movement Figure 5.10_1 Energy transformations in a car and a cell (part 1) Water Oxygen Energy conversion in a car 46

Energy for cellular work Water
Figure 5.10_2 Fuel Energy conversion Waste products Heat energy Cellular respiration Glucose Carbon dioxide   ATP ATP Figure 5.10_2 Energy transformations in a car and a cell (part 2) Oxygen Energy for cellular work Water Energy conversion in a cell 47

Heat, or thermal energy, is a type of kinetic energy associated with the random movement of atoms or molecules. Light is also a type of kinetic energy, and can be harnessed to power photosynthesis. Student Misconceptions and Concerns 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. Teaching Tips 1. 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). Consider challenging your students to come up with additional examples of such common energy conversions in their lives. 2. Some students can relate well to the concept of entropy as applied to the room where they live. Despite their cleaning up and organizing the room on a regular (or irregular) basis, the room becomes increasingly 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.” 3. The heat produced by the engine of a car is typically used to heat the car during cold weather. However, is this same heat available in warmer weather? Students are often unaware that their car “heaters” work 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 weather is warm. 4. Here is a question that might make cellular respiration a little more meaningful to your students. Ask your students 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? The answer is, 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. © 2012 Pearson Education, Inc. 48

Chemical energy is the potential energy available for release in a chemical reaction. It is the most important type of energy for living organisms to power the work of the cell. Student Misconceptions and Concerns 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. Teaching Tips 1. 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). Consider challenging your students to come up with additional examples of such common energy conversions in their lives. 2. Some students can relate well to the concept of entropy as applied to the room where they live. Despite their cleaning up and organizing the room on a regular (or irregular) basis, the room becomes increasingly 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.” 3. The heat produced by the engine of a car is typically used to heat the car during cold weather. However, is this same heat available in warmer weather? Students are often unaware that their car “heaters” work 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 weather is warm. 4. Here is a question that might make cellular respiration a little more meaningful to your students. Ask your students 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? The answer is, 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. Animation: Energy Concepts © 2012 Pearson Education, Inc. 49

Thermodynamics is the study of energy transformations that occur in a collection of matter. Scientists use the word system for the matter under study and surroundings for the rest of the universe. Student Misconceptions and Concerns 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. Teaching Tips 1. 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). Consider challenging your students to come up with additional examples of such common energy conversions in their lives. 2. Some students can relate well to the concept of entropy as applied to the room where they live. Despite their cleaning up and organizing the room on a regular (or irregular) basis, the room becomes increasingly 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.” 3. The heat produced by the engine of a car is typically used to heat the car during cold weather. However, is this same heat available in warmer weather? Students are often unaware that their car “heaters” work 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 weather is warm. 4. Here is a question that might make cellular respiration a little more meaningful to your students. Ask your students 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? The answer is, 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. © 2012 Pearson Education, Inc. 50

Two laws govern energy transformations in organisms. According to the first law of thermodynamics, energy in the universe is constant, and second law of thermodynamics, energy conversions increase the disorder of the universe. Entropy is the measure of disorder, or randomness. Student Misconceptions and Concerns 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. Teaching Tips 1. 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). Consider challenging your students to come up with additional examples of such common energy conversions in their lives. 2. Some students can relate well to the concept of entropy as applied to the room where they live. Despite their cleaning up and organizing the room on a regular (or irregular) basis, the room becomes increasingly 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.” 3. The heat produced by the engine of a car is typically used to heat the car during cold weather. However, is this same heat available in warmer weather? Students are often unaware that their car “heaters” work 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 weather is warm. 4. Here is a question that might make cellular respiration a little more meaningful to your students. Ask your students 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? The answer is, 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. © 2012 Pearson Education, Inc. 51

Cells use oxygen in reactions that release energy from fuel molecules. In cellular respiration, the chemical energy stored in organic molecules is converted to a form that the cell can use to perform work. Only about 25% of the chemical energy stored in gasoline is converted to kinetic energy. About 34% of the chemical energy in the fuel for cells gets converted to energy for cellular work. The rest is lost as heat. Student Misconceptions and Concerns 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. Teaching Tips 1. 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). Consider challenging your students to come up with additional examples of such common energy conversions in their lives. 2. Some students can relate well to the concept of entropy as applied to the room where they live. Despite their cleaning up and organizing the room on a regular (or irregular) basis, the room becomes increasingly 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.” 3. The heat produced by the engine of a car is typically used to heat the car during cold weather. However, is this same heat available in warmer weather? Students are often unaware that their car “heaters” work 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 weather is warm. 4. Here is a question that might make cellular respiration a little more meaningful to your students. Ask your students 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? The answer is, 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. © 2012 Pearson Education, Inc. 52

5.11 Chemical reactions either release or store energy
release energy (exergonic reactions) or require an input of energy and store energy (endergonic reactions). 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. 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. 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 clear that potential energy is stored in food as calories. Teaching Tips 1. The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) 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 lbs overweight, you would be nearly 40 lbs overweight if the same energy were stored as carbohydrates or proteins instead of fat). 2. The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon 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 liters 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-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100C, but it takes much more energy to melt ice or to convert boiling water into steam.) © 2012 Pearson Education, Inc. 53

Exergonic reactions release energy. These reactions release the energy in covalent bonds of the reactants. Burning wood releases the energy in glucose as heat and light. Cellular respiration involves many steps, releases energy slowly, and uses some of the released energy to produce ATP. 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. 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. 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 clear that potential energy is stored in food as calories. Teaching Tips 1. The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) 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 lbs overweight, you would be nearly 40 lbs overweight if the same energy were stored as carbohydrates or proteins instead of fat). 2. The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon 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 liters 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-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100C, but it takes much more energy to melt ice or to convert boiling water into steam.) © 2012 Pearson Education, Inc. 54

Amount of energy released
Figure 5.11A Reactants Amount of energy released Potential energy of molecules Energy Products Figure 5.11A Exergonic reaction, energy released 55

An endergonic reaction requires an input of energy and yields products rich in potential energy. Endergonic reactions begin with reactant molecules that contain relatively little potential energy but end with products that contain more chemical energy. 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. 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. 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 clear that potential energy is stored in food as calories. Teaching Tips 1. The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) 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 lbs overweight, you would be nearly 40 lbs overweight if the same energy were stored as carbohydrates or proteins instead of fat). 2. The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon 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 liters 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-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100C, but it takes much more energy to melt ice or to convert boiling water into steam.) © 2012 Pearson Education, Inc. 56

Amount of energy required
Figure 5.11B Products Amount of energy required Potential energy of molecules Energy Reactants Figure 5.11B Endergonic reaction, energy required 57

Photosynthesis is a type of endergonic process. Energy-poor reactants, carbon dioxide, and water are used. Energy is absorbed from sunlight. Energy-rich sugar molecules are produced. 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. 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. 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 clear that potential energy is stored in food as calories. Teaching Tips 1. The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) 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 lbs overweight, you would be nearly 40 lbs overweight if the same energy were stored as carbohydrates or proteins instead of fat). 2. The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon 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 liters 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-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100C, but it takes much more energy to melt ice or to convert boiling water into steam.) © 2012 Pearson Education, Inc. 58

A living organism carries out thousands of endergonic and exergonic chemical reactions. The total of an organism’s chemical reactions is called metabolism. A metabolic pathway is a series of chemical reactions that either builds a complex molecule or breaks down a complex molecule into simpler compounds. 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. 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. 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 clear that potential energy is stored in food as calories. Teaching Tips 1. The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) 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 lbs overweight, you would be nearly 40 lbs overweight if the same energy were stored as carbohydrates or proteins instead of fat). 2. The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon 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 liters 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-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100C, but it takes much more energy to melt ice or to convert boiling water into steam.) © 2012 Pearson Education, Inc. 59

Energy coupling uses the energy released from exergonic reactions to drive essential endergonic reactions, usually using the energy stored in ATP molecules. 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. 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. 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 clear that potential energy is stored in food as calories. Teaching Tips 1. The same mass of fat stores nearly twice as many calories (about 9 kcal per gram) 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 lbs overweight, you would be nearly 40 lbs overweight if the same energy were stored as carbohydrates or proteins instead of fat). 2. The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon 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 liters 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-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100C, but it takes much more energy to melt ice or to convert boiling water into steam.) © 2012 Pearson Education, Inc. 60

5.12 ATP drives cellular work by coupling exergonic and endergonic reactions
ATP, adenosine triphosphate, powers nearly all forms of cellular work. ATP consists of the nitrogenous base adenine, the five-carbon sugar ribose, and three phosphate groups. 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. Energy coupling 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 the employer. (We all might soon tire of a fast-food job that only paid its employees in food!) Money permits the coupling of a generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which allows us to make purchases in distant locations). This idea of earning and spending is a common concept we all know well. Teaching Tips 1. The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon 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 liters 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-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100°C, but it takes much more energy to melt ice or to convert boiling water into steam.) 2. When introducing ATP and ADP, consider asking your students to think of the terms as A-3-P and A-2-P, noting that the word roots tri = 3 and di = 2. 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 chemical components, the monomers of the cytoskeleton, and ADP are routinely recycled. There are several advantages common to human recycling of garbage and cellular recycling. 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). © 2012 Pearson Education, Inc. 61

Hydrolysis of ATP releases energy by transferring its third phosphate from ATP to some other molecule in a process called phosphorylation. Most cellular work depends on ATP energizing molecules by phosphorylating them. 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. Energy coupling 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 the employer. (We all might soon tire of a fast-food job that only paid its employees in food!) Money permits the coupling of a generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which allows us to make purchases in distant locations). This idea of earning and spending is a common concept we all know well. Teaching Tips 1. The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon 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 liters 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-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100°C, but it takes much more energy to melt ice or to convert boiling water into steam.) 2. When introducing ATP and ADP, consider asking your students to think of the terms as A-3-P and A-2-P, noting that the word roots tri = 3 and di = 2. 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 chemical components, the monomers of the cytoskeleton, and ADP are routinely recycled. There are several advantages common to human recycling of garbage and cellular recycling. 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). © 2012 Pearson Education, Inc. 62

ATP: Adenosine Triphosphate Phosphate group P P P Adenine Ribose
Figure 5.12A_s1 ATP: Adenosine Triphosphate Phosphate group P P P Adenine Ribose Figure 5.12A_s1 The structure and hydrolysis of ATP (step 1) 63

ATP: Adenosine Triphosphate Phosphate group P P P Adenine Ribose H2O
Figure 5.12A_s2 ATP: Adenosine Triphosphate Phosphate group P P P Adenine Ribose H2O Hydrolysis Figure 5.12A_s2 The structure and hydrolysis of ATP (step 2) P P P Energy ADP: Adenosine Diphosphate 64

There are three main types of cellular work: chemical, mechanical, and transport. ATP drives all three of these types of work. 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. Energy coupling 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 the employer. (We all might soon tire of a fast-food job that only paid its employees in food!) Money permits the coupling of a generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which allows us to make purchases in distant locations). This idea of earning and spending is a common concept we all know well. Teaching Tips 1. The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon 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 liters 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-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100°C, but it takes much more energy to melt ice or to convert boiling water into steam.) 2. When introducing ATP and ADP, consider asking your students to think of the terms as A-3-P and A-2-P, noting that the word roots tri = 3 and di = 2. 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 chemical components, the monomers of the cytoskeleton, and ADP are routinely recycled. There are several advantages common to human recycling of garbage and cellular recycling. 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). © 2012 Pearson Education, Inc. 65

Protein filament moved Solute transported
Figure 5.12B Chemical work Mechanical work Transport work ATP ATP ATP Solute P Motor protein P P Reactants Membrane protein P Figure 5.12B How ATP powers cellular work P P Product Molecule formed Protein filament moved Solute transported ADP P ADP P ADP P 66

ATP is a renewable source of energy for the cell. In the ATP cycle, energy released in an exergonic reaction, such as the breakdown of glucose,is used in an endergonic reaction to generate ATP. 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. Energy coupling 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 the employer. (We all might soon tire of a fast-food job that only paid its employees in food!) Money permits the coupling of a generation of value (a paycheck, analogous to an energy-releasing reaction) to an energy-consuming reaction (money, which allows us to make purchases in distant locations). This idea of earning and spending is a common concept we all know well. Teaching Tips 1. The amount of energy each adult human needs to generate the ATP required in a day is tremendous. Here is a calculation that has impressed many students. Depending upon 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 liters 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-liter bottles, you can help students visualize how much liquid water can be raised from 0 to 100C. (Note: 100 calories raises about 1 liter of water 100°C, but it takes much more energy to melt ice or to convert boiling water into steam.) 2. When introducing ATP and ADP, consider asking your students to think of the terms as A-3-P and A-2-P, noting that the word roots tri = 3 and di = 2. 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 chemical components, the monomers of the cytoskeleton, and ADP are routinely recycled. There are several advantages common to human recycling of garbage and cellular recycling. 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). © 2012 Pearson Education, Inc. 67

Energy from exergonic reactions Energy for endergonic reactions
Figure 5.12C ATP Phosphorylation Hydrolysis Energy from exergonic reactions Energy for endergonic reactions Figure 5.12C The ATP cycle ADP P 68

5.13 Enzymes speed up the cell’s chemical reactions by lowering energy barriers
Although biological molecules possess much potential energy, it is not released spontaneously. An energy barrier must be overcome before a chemical reaction can begin. This energy is called the activation energy (EA). Student Misconceptions and Concerns 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 is much greater than the input. Teaching Tips The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, 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, proteins with the ability to promote the production of carbohydrates and lipids. © 2012 Pearson Education, Inc. 70

5.13 Enzymes speed up the cell’s chemical reactions by lowering energy barriers
We can think of EA as the amount of energy needed for a reactant molecule to move “uphill” to a higher energy but an unstable state so that the “downhill” part of the reaction can begin. One way to speed up a reaction is to add heat, which agitates atoms so that bonds break more easily and reactions can proceed but could kill a cell. Student Misconceptions and Concerns 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 is much greater than the input. Teaching Tips The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, 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, proteins with the ability to promote the production of carbohydrates and lipids. © 2012 Pearson Education, Inc. 71

Activation energy barrier
Figure 5.13A Activation energy barrier Enzyme Activation energy barrier reduced by enzyme Reactant Reactant Energy Energy Figure 5.13A The effect of an enzyme in lowering EA Products Products Without enzyme With enzyme 72

Activation energy barrier
Figure 5.13A_1 Activation energy barrier Reactant Energy Figure 5.13A_1 The effect of an enzyme in lowering EA (part 1) Products Without enzyme 73

Activation energy barrier reduced by enzyme
Figure 5.13A_2 Enzyme Activation energy barrier reduced by enzyme Reactant Energy Figure 5.13A_2 The effect of an enzyme in lowering EA (part 2) Products With enzyme 74

Progress of the reaction
Figure 5.13Q a b Energy Reactants c Figure 5.13Q Activation energy with and without an enzyme Products Progress of the reaction 75

Animation: How Enzymes Work
5.13 Enzymes speed up the cell’s chemical reactions by lowering energy barriers Enzymes function as biological catalysts by lowering the EA needed for a reaction to begin, increase the rate of a reaction without being consumed by the reaction, and are usually proteins, although some RNA molecules can function as enzymes. Student Misconceptions and Concerns 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 is much greater than the input. Teaching Tips The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, 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, proteins with the ability to promote the production of carbohydrates and lipids. Animation: How Enzymes Work © 2012 Pearson Education, Inc. 76

5.14 A specific enzyme catalyzes each cellular reaction
An enzyme is very selective in the reaction it catalyzes and has a shape that determines the enzyme’s specificity. The specific reactant that an enzyme acts on is called the enzyme’s substrate. A substrate fits into a region of the enzyme called the active site. Enzymes are specific because their active site fits only specific substrate molecules. Student Misconceptions and Concerns 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. Just like pitching a tent, new concepts are best constructed with many lines of support. Teaching Tips 1. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, 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, proteins with the ability to promote the production of carbohydrates and lipids. 2. 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. © 2012 Pearson Education, Inc. 77

The following figure illustrates the catalytic cycle of an enzyme. Student Misconceptions and Concerns 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. Just like pitching a tent, new concepts are best constructed with many lines of support. Teaching Tips 1. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, 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, proteins with the ability to promote the production of carbohydrates and lipids. 2. 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. © 2012 Pearson Education, Inc. 78

Enzyme available with empty active site
Figure 5.14_s1 1 Enzyme available with empty active site Active site Enzyme (sucrase) Figure 5.14_s1 The catalytic cycle of an enzyme (step 1) 79

Figure 5.14_s2 1 Enzyme available with empty active site Active site Substrate (sucrose) 2 Substrate binds to enzyme with induced fit Enzyme (sucrase) Figure 5.14_s2 The catalytic cycle of an enzyme (step 2) 80

Figure 5.14_s3 1 Enzyme available with empty active site Active site Substrate (sucrose) 2 Substrate binds to enzyme with induced fit Enzyme (sucrase) H2O Figure 5.14_s3 The catalytic cycle of an enzyme (step 3) 3 Substrate is converted to products 81

Figure 5.14_s4 1 Enzyme available with empty active site Active site Substrate (sucrose) 2 Substrate binds to enzyme with induced fit Enzyme (sucrase) Glucose Fructose H2O Figure 5.14_s4 The catalytic cycle of an enzyme (step 4) 4 Products are released 3 Substrate is converted to products 82

For every enzyme, there are optimal conditions under which it is most effective. Temperature affects molecular motion. An enzyme’s optimal temperature produces the highest rate of contact between the reactants and the enzyme’s active site. Most human enzymes work best at 35–40ºC. The optimal pH for most enzymes is near neutrality. Student Misconceptions and Concerns 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. Just like pitching a tent, new concepts are best constructed with many lines of support. Teaching Tips 1. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, 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, proteins with the ability to promote the production of carbohydrates and lipids. 2. 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. © 2012 Pearson Education, Inc. 83

Many enzymes require nonprotein helpers called cofactors, which bind to the active site and function in catalysis. Some cofactors are inorganic, such as zinc, iron, or copper. If a cofactor is an organic molecule, such as most vitamins, it is called a coenzyme. Student Misconceptions and Concerns 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. Just like pitching a tent, new concepts are best constructed with many lines of support. Teaching Tips 1. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, 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, proteins with the ability to promote the production of carbohydrates and lipids. 2. 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. © 2012 Pearson Education, Inc. 84

5.15 Enzyme inhibitors can regulate enzyme activity in a cell
A chemical that interferes with an enzyme’s activity is called an inhibitor. Competitive inhibitors block substrates from entering the active site and reduce an enzyme’s productivity. Student Misconceptions and Concerns 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. Just like pitching a tent, new concepts are best constructed with many lines of support. Teaching Tips 1. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, 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, proteins with the ability to promote the production of carbohydrates and lipids. 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. Feedback inhibition relies upon the negative feedback of the accumulation of a product. Ask students in class 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.) © 2012 Pearson Education, Inc. 85

Noncompetitive inhibitors bind to the enzyme somewhere other than the active site, change the shape of the active site, and prevent the substrate from binding. Student Misconceptions and Concerns 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. Just like pitching a tent, new concepts are best constructed with many lines of support. Teaching Tips 1. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, 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, proteins with the ability to promote the production of carbohydrates and lipids. 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. Feedback inhibition relies upon the negative feedback of the accumulation of a product. Ask students in class 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.) © 2012 Pearson Education, Inc. 86

Normal binding of substrate
Figure 5.15A Substrate Active site Enzyme Allosteric site Normal binding of substrate Competitive inhibitor Noncompetitive inhibitor Figure 5.15A How inhibitors interfere with substrate binding Enzyme inhibition 87

Enzyme inhibitors are important in regulating cell metabolism. In some reactions, the product may act as an inhibitor of one of the enzymes in the pathway that produced it. This is called feedback inhibition. Student Misconceptions and Concerns 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. Just like pitching a tent, new concepts are best constructed with many lines of support. Teaching Tips 1. The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, 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, proteins with the ability to promote the production of carbohydrates and lipids. 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. Feedback inhibition relies upon the negative feedback of the accumulation of a product. Ask students in class 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.) © 2012 Pearson Education, Inc. 88

Feedback inhibition Enzyme 1 Enzyme 2 Enzyme 3 A B C D Reaction 1
Figure 5.15B Feedback inhibition Enzyme 1 Enzyme 2 Enzyme 3 A B C D Reaction 1 Reaction 2 Reaction 3 Starting molecule Product Figure 5.15B Feedback inhibition of a biosynthetic pathway 89

5.16 CONNECTION: Many drugs, pesticides, and poisons are enzyme inhibitors
Many beneficial drugs act as enzyme inhibitors, including Ibuprofen, inhibiting the production of prostaglandins, some blood pressure medicines, some antidepressants, many antibiotics, and protease inhibitors used to fight HIV. Enzyme inhibitors have also been developed as pesticides and deadly poisons for chemical warfare. Teaching Tips Challenge your class to identify advantages of specific enzyme inhibitors for pest control. These advantages 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. © 2012 Pearson Education, Inc. 90

Figure 5.16 Figure 5.16 Ibuprofen, an enzyme inhibitor 91

You should now be able to
Describe the fluid mosaic structure of cell membranes. Describe the diverse functions of membrane proteins. Relate the structure of phospholipid molecules to the structure and properties of cell membranes. Define diffusion and describe the process of passive transport. © 2012 Pearson Education, Inc. 92

Explain how osmosis can be defined as the diffusion of water across a membrane. Distinguish between hypertonic, hypotonic, and isotonic solutions. Explain how transport proteins facilitate diffusion. Distinguish between exocytosis, endocytosis, phagocytosis, pinocytosis, and receptor-mediated endocytosis. © 2012 Pearson Education, Inc. 93

Define and compare kinetic energy, potential energy, chemical energy, and heat. Define the two laws of thermodynamics and explain how they relate to biological systems. Define and compare endergonic and exergonic reactions. Explain how cells use cellular respiration and energy coupling to survive. © 2012 Pearson Education, Inc. 94

Explain how ATP functions as an energy shuttle. Explain how enzymes speed up chemical reactions. Explain how competitive and noncompetitive inhibitors alter an enzyme’s activity. Explain how certain drugs, pesticides, and poisons can affect enzymes. © 2012 Pearson Education, Inc. 95

Passive transport (requires no energy)
Figure 5.UN01 Passive transport (requires no energy) Active transport (requires energy) Diffusion Facilitated diffusion Osmosis HIgher solute concentration HIgher free water concentration HIgher solute concentration Solute Figure 5.UN01 Reviewing the Concepts, 5.8 ATP Water Lower free water concentration Lower solute concentration Lower solute concentration 96

Energy from exergonic reactions Energy for endergonic reactions
Figure 5.UN02 ATP cycle ATP Energy from exergonic reactions Energy for endergonic reactions Figure 5.UN02 Reviewing the Concepts, 5.12 ADP P 97

Molecules cross cell membranes polar molecules and ions
Figure 5.UN03 Molecules cross cell membranes by by passive transport (a) may be moving down moving against requires ATP (b) uses diffusion (d) Figure 5.UN03 Connecting the Concepts, question 1 uses (e) of of polar molecules and ions (c) 98

Figure 5.UN04 c. b. a. d. f. Figure 5.UN04 Connecting the Concepts, question 2 e. 99

Table 5.UN05 Table 5.UN05 Applying the Concepts, question 16 100

Rate of reaction 1 2 3 4 5 6 7 8 9 10 pH Figure 5.UN06
Figure 5.UN06 Applying the Concepts, question 17 1 2 3 4 5 6 7 8 9 10 pH 101

Chapter 5 The Working Cell.

Similar presentations

Presentation on theme: "Chapter 5 The Working Cell."— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Chapter 5 The Working Cell.

Similar presentations

Presentation on theme: "Chapter 5 The Working Cell."— Presentation transcript:

Similar presentations

About project

Feedback