How Cells Harvest Chemical Energy

How Cells Harvest Chemical Energy
Chapter 6 How Cells Harvest Chemical Energy

Introduction In eukaryotes, cellular respiration
harvests energy from food, yields large amounts of ATP, and Uses ATP to drive cellular work. A similar process takes place in many prokaryotic organisms. © 2012 Pearson Education, Inc. 2

Cellular Respiration: Aerobic Harvesting of Energy
Figure 6.0_1 Chapter 6: Big Ideas Cellular Respiration: Aerobic Harvesting of Energy Stages of Cellular Respiration Figure 6.0_1 Chapter 6: Big Ideas Fermentation: Anaerobic Harvesting of Energy Connections Between Metabolic Pathways 3

Figure 6.0_2 Figure 6.0_2 Lemur leaping 4

CELLULAR RESPIRATION: AEROBIC HARVESTING OF ENERGY
© 2012 Pearson Education, Inc. 5

6.1 Photosynthesis and cellular respiration provide energy for life
Life requires energy. In almost all ecosystems, energy ultimately comes from the sun. In photosynthesis, some of the energy in sunlight is captured by chloroplasts, atoms of carbon dioxide and water are rearranged, and glucose and oxygen are produced. Student Misconceptions and Concerns Students should be cautioned against the assumption that energy is created when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics addressed in Module 5.10). Teaching Tips 1. You might wish to elaborate on the amount of solar energy striking Earth. Every day Earth is bombarded with solar radiation equal to the energy of 100 million atomic bombs. Of the tiny fraction of light that reaches photosynthetic organisms, only about 1% is converted to chemical energy by photosynthesis. 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. © 2012 Pearson Education, Inc. 6

6.1 Photosynthesis and cellular respiration provide energy for life
In cellular respiration glucose is broken down to carbon dioxide and water and the cell captures some of the released energy to make ATP. Cellular respiration takes place in the mitochondria of eukaryotic cells. Student Misconceptions and Concerns Students should be cautioned against the assumption that energy is created when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics addressed in Module 5.10). Teaching Tips 1. You might wish to elaborate on the amount of solar energy striking Earth. Every day Earth is bombarded with solar radiation equal to the energy of 100 million atomic bombs. Of the tiny fraction of light that reaches photosynthetic organisms, only about 1% is converted to chemical energy by photosynthesis. 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. © 2012 Pearson Education, Inc. 7

Photosynthesis in chloroplasts Cellular respiration in mitochondria
Figure 6.1 Sunlight energy ECOSYSTEM Photosynthesis in chloroplasts CO2 Glucose H2O O2 Cellular respiration in mitochondria Figure 6.1 The connection between photosynthesis and cellular respiration (for cellular work) ATP Heat energy 8

Photosynthesis in chloroplasts Cellular respiration in mitochondria
Figure 6.1_1 Sunlight energy ECOSYSTEM Photosynthesis in chloroplasts CO2 Glucose H2O O2 Cellular respiration in mitochondria Figure 6.1_1 The connection between photosynthesis and cellular respiration (for cellular work) ATP Heat energy 9

Figure 6.1_2 Figure 6.1_2 The connection between photosynthesis and cellular respiration 10

6.2 Breathing supplies O2 for use in cellular respiration and removes CO2
Respiration, as it relates to breathing, and cellular respiration are not the same. Respiration, in the breathing sense, refers to an exchange of gases. Usually an organism brings in oxygen from the environment and releases waste CO2. Cellular respiration is the aerobic (oxygen requiring) harvesting of energy from food molecules by cells. Student Misconceptions and Concerns Students should be cautioned against the assumption that energy is created when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics addressed in Module 5.10). Teaching Tips 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. © 2012 Pearson Education, Inc. 11

Muscle cells carrying out
Figure 6.2 Breathing O2 CO2 Lungs CO2 Bloodstream O2 Figure 6.2 The connection between breathing and cellular respiration Muscle cells carrying out Cellular Respiration Glucose  O2 CO2  H2O  ATP 12

Muscle cells carrying out
Figure 6.2_1 Breathing O2 CO2 Lungs CO2 Bloodstream O2 Figure 6.2_1 The connection between breathing and cellular respiration Muscle cells carrying out Cellular Respiration Glucose  O2 CO2  H2O  ATP 13

Figure 6.2_2 Figure 6.2_2 The connection between breathing and cellular respiration 14

6.3 Cellular respiration banks energy in ATP molecules
Cellular respiration is an exergonic process that transfers energy from the bonds in glucose to form ATP. Cellular respiration produces up to 32 ATP molecules from each glucose molecule and captures only about 34% of the energy originally stored in glucose. Other foods (organic molecules) can also be used as a source of energy. Student Misconceptions and Concerns 1. Students should be cautioned against the assumption that energy is created when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics addressed in Module 5.10). 2. Students often fail to realize that aerobic metabolism is a process generally similar to the burning of wood or the burning of gasoline in an automobile engine. Noting these general similarities can help students comprehend the overall reaction and heat generation associated with these processes. Teaching Tips 1. 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. 2. During cellular respiration, our cells convert about 34% of our food energy to useful work (Module 6.3). The other 66% of the energy is released as heat. We use this heat to maintain a relatively steady body temperature near 37C (98–99F). This is about the same amount of heat generated by a 75-watt incandescent light bulb. If you choose to include a discussion of heat generation from aerobic metabolism, consider the following. a. Ask your students why they feel warm when it is 30C (86F) outside, if their core body temperature is about 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 body temperature around 37C. Thus, we sweat and behave in ways that helps us get rid of the extra heat from cellular respiration. b. Share this calculation with your students. Depending upon a person’s size and level of activity, 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! (Note: Consider bringing a 2-liter bottle as a visual aid, or ten 2-liter bottles to make the point above. It takes 100 calories to raise 1 liter of water 100C; it takes much more energy to melt ice or evaporate water as steam.) © 2012 Pearson Education, Inc. 15

Glucose Oxygen Carbon dioxide Water  Heat C6H12O6 6 O2 6 CO2 6 H2O
Figure 6.3 C6H12O6 6 O2 6 CO2 6 H2O ATP Glucose Oxygen Carbon dioxide Water  Heat Figure 6.3 Summary equation for cellular respiration 16

6.4 CONNECTION: The human body uses energy from ATP for all its activities
The average adult human needs about 2,200 kcal of energy per day. About 75% of these calories are used to maintain a healthy body. The remaining 25% is used to power physical activities. Student Misconceptions and Concerns Students should be cautioned against the assumption that energy is created when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics addressed in Module 5.10). Teaching Tips You might share with your students that it takes about 10 million ATP molecules per second to power one active muscle cell. © 2012 Pearson Education, Inc. 17

6.4 CONNECTION: The human body uses energy from ATP for all its activities
A kilocalorie (kcal) is the quantity of heat required to raise the temperature of 1 kilogram (kg) of water by 1oC, the same as a food Calorie, and used to measure the nutritional values indicated on food labels. Student Misconceptions and Concerns Students should be cautioned against the assumption that energy is created when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics addressed in Module 5.10). Teaching Tips You might share with your students that it takes about 10 million ATP molecules per second to power one active muscle cell. © 2012 Pearson Education, Inc. 18

kcal consumed per hour by a 67.5-kg (150-lb) person*
Figure 6.4 Activity kcal consumed per hour by a 67.5-kg (150-lb) person* Running (8–9 mph) 979 Dancing (fast) 510 Bicycling (10 mph) 490 Swimming (2 mph) 408 Walking (4 mph) 341 Walking (3 mph) 245 Dancing (slow) 204 Driving a car 61 Figure 6.4 Energy consumed by various activities Sitting (writing) 28 *Not including kcal needed for body maintenance 19

kcal consumed per hour by a 67.5-kg (150-lb) person*
Figure 6.4_1 Activity kcal consumed per hour by a 67.5-kg (150-lb) person* Running (8–9 mph) 979 Dancing (fast) 510 Bicycling (10 mph) 490 Swimming (2 mph) 408 Walking (4 mph) 341 Walking (3 mph) 245 Dancing (slow) Figure 6.4_1 Energy consumed by various activities 204 Driving a car 61 Sitting (writing) 28 *Not including kcal needed for body maintenance 20

Figure 6.4_2 Figure 6.4_2 Energy consumed by various activities 21

6.5 Cells tap energy from electrons “falling” from organic fuels to oxygen
The energy necessary for life is contained in the arrangement of electrons in chemical bonds in organic molecules. An important question is how do cells extract this energy? Student Misconceptions and Concerns 1. Students should be cautioned against the assumption that energy is created when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics addressed in Module 5.10). 2. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel becomes wasteful, reducing the efficiencies of the systems. Teaching Tips The use of the word falling when discussing the movement of electrons in a redox reaction can be confusing. Consider explaining the use of the term falling, in reference to the potential energy of a falling object. © 2012 Pearson Education, Inc. 22

When the carbon-hydrogen bonds of glucose are broken, electrons are transferred to oxygen. Oxygen has a strong tendency to attract electrons. An electron loses potential energy when it “falls” to oxygen. Student Misconceptions and Concerns 1. Students should be cautioned against the assumption that energy is created when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics addressed in Module 5.10). 2. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel becomes wasteful, reducing the efficiencies of the systems. Teaching Tips The use of the word falling when discussing the movement of electrons in a redox reaction can be confusing. Consider explaining the use of the term falling, in reference to the potential energy of a falling object. © 2012 Pearson Education, Inc. 23

Energy can be released from glucose by simply burning it. The energy is dissipated as heat and light and is not available to living organisms. Student Misconceptions and Concerns 1. Students should be cautioned against the assumption that energy is created when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics addressed in Module 5.10). 2. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel becomes wasteful, reducing the efficiencies of the systems. Teaching Tips The use of the word falling when discussing the movement of electrons in a redox reaction can be confusing. Consider explaining the use of the term falling, in reference to the potential energy of a falling object. © 2012 Pearson Education, Inc. 24

On the other hand, cellular respiration is the controlled breakdown of organic molecules. Energy is gradually released in small amounts, captured by a biological system, and stored in ATP. Student Misconceptions and Concerns 1. Students should be cautioned against the assumption that energy is created when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics addressed in Module 5.10). 2. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel becomes wasteful, reducing the efficiencies of the systems. Teaching Tips The use of the word falling when discussing the movement of electrons in a redox reaction can be confusing. Consider explaining the use of the term falling, in reference to the potential energy of a falling object. © 2012 Pearson Education, Inc. 25

The movement of electrons from one molecule to another is an oxidation-reduction reaction, or redox reaction. In a redox reaction, the loss of electrons from one substance is called oxidation, the addition of electrons to another substance is called reduction, a molecule is oxidized when it loses one or more electrons, and reduced when it gains one or more electrons. Student Misconceptions and Concerns 1. Students should be cautioned against the assumption that energy is created when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics addressed in Module 5.10). 2. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel becomes wasteful, reducing the efficiencies of the systems. Teaching Tips The use of the word falling when discussing the movement of electrons in a redox reaction can be confusing. Consider explaining the use of the term falling, in reference to the potential energy of a falling object. © 2012 Pearson Education, Inc. 26

A cellular respiration equation is helpful to show the changes in hydrogen atom distribution. Glucose loses its hydrogen atoms and becomes oxidized to CO2. Oxygen gains hydrogen atoms and becomes reduced to H2O. Student Misconceptions and Concerns 1. Students should be cautioned against the assumption that energy is created when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics addressed in Module 5.10). 2. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel becomes wasteful, reducing the efficiencies of the systems. Teaching Tips The use of the word falling when discussing the movement of electrons in a redox reaction can be confusing. Consider explaining the use of the term falling, in reference to the potential energy of a falling object. © 2012 Pearson Education, Inc. 27

Loss of hydrogen atoms (becomes oxidized)
Figure 6.5A Loss of hydrogen atoms (becomes oxidized) C6H12O6 6 O2 6 CO2 6 H2O ATP Glucose  Heat Gain of hydrogen atoms (becomes reduced) Figure 6.5A Rearrangement of hydrogen atoms (with their electrons) in the redox reactions of cellular respiration 28

Enzymes are necessary to oxidize glucose and other foods. NAD+ is an important enzyme in oxidizing glucose, accepts electrons, and becomes reduced to NADH. Student Misconceptions and Concerns 1. Students should be cautioned against the assumption that energy is created when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics addressed in Module 5.10). 2. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel becomes wasteful, reducing the efficiencies of the systems. Teaching Tips The use of the word falling when discussing the movement of electrons in a redox reaction can be confusing. Consider explaining the use of the term falling, in reference to the potential energy of a falling object. © 2012 Pearson Education, Inc. 29

Becomes oxidized 2H Becomes reduced NAD 2H NADH H
Figure 6.5B Becomes oxidized 2H Becomes reduced NAD 2H NADH H Figure 6.5B A pair of redox reactions occuring simultaneously (carries 2 electrons) 2 H 2 30

There are other electron “carrier” molecules that function like NAD+. They form a staircase where the electrons pass from one to the next down the staircase. These electron carriers collectively are called the electron transport chain. As electrons are transported down the chain, ATP is generated. Student Misconceptions and Concerns 1. Students should be cautioned against the assumption that energy is created when it is converted from one form to another. This might be a good time to review the principle of conservation of energy (the first law of thermodynamics addressed in Module 5.10). 2. The advantage of the gradual degradation of glucose may not be obvious to some students. Many analogies exist that reveal the advantages of short and steady steps. Fuel in an automobile is burned slowly to best utilize the energy released from the fuel. A few fireplace logs release gradual heat to keep a room temperature steady. In both situations, excessive use of fuel becomes wasteful, reducing the efficiencies of the systems. Teaching Tips The use of the word falling when discussing the movement of electrons in a redox reaction can be confusing. Consider explaining the use of the term falling, in reference to the potential energy of a falling object. © 2012 Pearson Education, Inc. 31

Controlled release of energy for synthesis of ATP H
Figure 6.5C NADH NAD ATP 2 Controlled release of energy for synthesis of ATP H Electron transport chain Figure 6.5C In cellular respiration, electrons fall down an energy staircase and finally reduce O2. 2 2 1 2 H O2 H2O 32

STAGES OF CELLULAR RESPIRATION

6.6 Overview: Cellular respiration occurs in three main stages
Cellular respiration consists of a sequence of steps that can be divided into three stages. Stage 1 – Glycolysis Stage 2 – Pyruvate oxidation and citric acid cycle Stage 3 – Oxidative phosphorylation Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips The production of NADH through glycolysis and the Krebs cycle, as compared to the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have value to be cashed in by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the electron transport cashier. © 2012 Pearson Education, Inc. 34

Stage 1: Glycolysis occurs in the cytoplasm, begins cellular respiration, and breaks down glucose into two molecules of a three-carbon compound called pyruvate. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips The production of NADH through glycolysis and the Krebs cycle, as compared to the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have value to be cashed in by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the electron transport cashier. © 2012 Pearson Education, Inc. 35

Stage 2: The citric acid cycle takes place in mitochondria, oxidizes pyruvate to a two-carbon compound, and supplies the third stage with electrons. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips The production of NADH through glycolysis and the Krebs cycle, as compared to the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have value to be cashed in by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the electron transport cashier. © 2012 Pearson Education, Inc. 36

Stage 3: Oxidative phosphorylation involves electrons carried by NADH and FADH2, shuttles these electrons to the electron transport chain embedded in the inner mitochondrial membrane, involves chemiosmosis, and generates ATP through oxidative phosphorylation associated with chemiosmosis. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips The production of NADH through glycolysis and the Krebs cycle, as compared to the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have value to be cashed in by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the electron transport cashier. © 2012 Pearson Education, Inc. 37

Electrons carried by NADH NADH FADH2
Figure 6.6 CYTOPLASM NADH Electrons carried by NADH NADH FADH2 Glycolysis Oxidative Phosphorylation (electron transport and chemiosmosis) Pyruvate Oxidation Glucose Pyruvate Citric Acid Cycle Figure 6.6 An overview of cellular respiration Mitochondrion ATP Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation ATP ATP 38

Electrons carried by NADH NADH FADH2
Figure 6.6_1 CYTOPLASM NADH Electrons carried by NADH NADH FADH2 Glycolysis Oxidative Phosphorylation (electron transport and chemiosmosis) Pyruvate Oxidation Citric Acid Cycle Glucose Pyruvate Figure 6.6_1 An overview of cellular respiration Mitochondrion ATP ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation 39

6.7 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
In glycolysis, a single molecule of glucose is enzymatically cut in half through a series of steps, two molecules of pyruvate are produced, two molecules of NAD+ are reduced to two molecules of NADH, and a net of two molecules of ATP is produced. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips The production of NADH through glycolysis and the Krebs cycle, as compared to the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have value to be cashed in by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the electron transport cashier. © 2012 Pearson Education, Inc. 40

Glucose 2 ADP 2 NAD 2 P 2 NADH ATP 2 2 H 2 Pyruvate Figure 6.7A
Figure 6.7A An overview of glycolysis 2 Pyruvate 41

ATP is formed in glycolysis by substrate-level phosphorylation during which an enzyme transfers a phosphate group from a substrate molecule to ADP and ATP is formed. The compounds that form between the initial reactant, glucose, and the final product, pyruvate, are called intermediates. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips The production of NADH through glycolysis and the Krebs cycle, as compared to the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have value to be cashed in by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the electron transport cashier. © 2012 Pearson Education, Inc. 42

Enzyme Enzyme P ADP ATP P P Substrate Product Figure 6.7B
Figure 6.7B Substrate-level phosphorylation: transfer of a phosphate group from a substrate to ADP, producing ATP P P Substrate Product 43

The steps of glycolysis can be grouped into two main phases. In steps 1–4, the energy investment phase, energy is consumed as two ATP molecules are used to energize a glucose molecule, which is then split into two small sugars that are now primed to release energy. In steps 5–9, the energy payoff, two NADH molecules are produced for each initial glucose molecule and ATP molecules are generated. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips The production of NADH through glycolysis and the Krebs cycle, as compared to the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have value to be cashed in by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the electron transport cashier. © 2012 Pearson Education, Inc. 44

ENERGY INVESTMENT PHASE
Figure 6.7Ca_s1 Glucose ENERGY INVESTMENT PHASE Steps – A fuel molecule is energized, using ATP. 1 3 ATP Step 1 ADP P Glucose 6-phosphate 2 P Fructose 6-phosphate ATP 3 ADP Figure 6.7Ca_s1 Details of glycolysis: energy investment phase (step 1) Fructose 1,6-bisphosphate P P 45

ENERGY INVESTMENT PHASE
Figure 6.7Ca_s2 Glucose ENERGY INVESTMENT PHASE Steps – A fuel molecule is energized, using ATP. 1 3 ATP Step 1 ADP P Glucose 6-phosphate 2 P Fructose 6-phosphate ATP 3 ADP Figure 6.7Ca_s2 Details of glycolysis: energy investment phase (step 2) Step A six-carbon intermediate splits into two three-carbon intermediates. 4 Fructose 1,6-bisphosphate P P 4 Glyceraldehyde 3-phosphate (G3P) P P 46

Step A redox reaction generates NADH. 5 5 5
Figure 6.7Cb_s1 P P ENERGY PAYOFF PHASE Step A redox reaction generates NADH. 5 NAD 5 NAD 5 NADH P P NADH H H P P P P 1,3-Bisphospho- glycerate Figure 6.7Cb_s1 Details of glycolysis: energy payoff phase (step 1) 47

Step A redox reaction generates NADH. 5 5 5
Figure 6.7Cb_s2 P P ENERGY PAYOFF PHASE Step A redox reaction generates NADH. 5 NAD 5 NAD 5 NADH P P NADH H H P P P P 1,3-Bisphospho- glycerate ADP ADP 6 6 Steps – ATP and pyruvate are produced. 6 9 ATP ATP P P 3-Phospho- glycerate 7 7 P P 2-Phospho- glycerate Figure 6.7Cb_s2 Details of glycolysis: energy payoff phase (step 2) 8 8 H2O H2O P P Phosphoenol- pyruvate (PEP) ADP ADP 9 9 ATP ATP Pyruvate 48

6.8 Pyruvate is oxidized prior to the citric acid cycle
The pyruvate formed in glycolysis is transported from the cytoplasm into a mitochondrion where the citric acid cycle and oxidative phosphorylation will occur. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips The production of NADH through glycolysis and the Krebs cycle, as compared to the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have value to be cashed in by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the electron transport cashier. © 2012 Pearson Education, Inc. 49

6.8 Pyruvate is oxidized prior to the citric acid cycle
Two molecules of pyruvate are produced for each molecule of glucose that enters glycolysis. Pyruvate does not enter the citric acid cycle, but undergoes some chemical grooming in which a carboxyl group is removed and given off as CO2, the two-carbon compound remaining is oxidized while a molecule of NAD+ is reduced to NADH, coenzyme A joins with the two-carbon group to form acetyl coenzyme A, abbreviated as acetyl CoA, and acetyl CoA enters the citric acid cycle. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips The production of NADH through glycolysis and the Krebs cycle, as compared to the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have value to be cashed in by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the electron transport cashier. © 2012 Pearson Education, Inc. 50

NAD NADH H CoA Pyruvate Acetyl coenzyme A CO2 Coenzyme A 2 1 3
Figure 6.8 NAD NADH H 2 CoA Pyruvate 1 Acetyl coenzyme A 3 Figure 6.8 The link between glycolysis and the citric acid cycle CO2 Coenzyme A 51

6.9 The citric acid cycle completes the oxidation of organic molecules, generating many NADH and FADH2 molecules The citric acid cycle is also called the Krebs cycle (after the German-British researcher Hans Krebs, who worked out much of this pathway in the 1930s), completes the oxidation of organic molecules, and generates many NADH and FADH2 molecules. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips The production of NADH through glycolysis and the Krebs cycle, as compared to the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have value to be cashed in by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the electron transport cashier. © 2012 Pearson Education, Inc. 52

Acetyl CoA Citric Acid Cycle CoA CoA 2 CO2 3 NAD FADH2 FAD 3 NADH
Figure 6.9A Acetyl CoA CoA CoA 2 CO2 Citric Acid Cycle 3 NAD FADH2 Figure 6.9A An overview of the citric acid cycle FAD 3 NADH 3 H ATP ADP P 53

6.9 The citric acid cycle completes the oxidation of organic molecules, generating many NADH and FADH2 molecules During the citric acid cycle the two-carbon group of acetyl CoA is added to a four-carbon compound, forming citrate, citrate is degraded back to the four-carbon compound, two CO2 are released, and 1 ATP, 3 NADH, and 1 FADH2 are produced. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips The production of NADH through glycolysis and the Krebs cycle, as compared to the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have value to be cashed in by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the electron transport cashier. © 2012 Pearson Education, Inc. 54

6.9 The citric acid cycle completes the oxidation of organic molecules, generating many NADH and FADH2 molecules Remember that the citric acid cycle processes two molecules of acetyl CoA for each initial glucose. Thus, after two turns of the citric acid cycle, the overall yield per glucose molecule is 2 ATP, 6 NADH, and 2 FADH2. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips The production of NADH through glycolysis and the Krebs cycle, as compared to the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have value to be cashed in by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the electron transport cashier. © 2012 Pearson Education, Inc. 55

Step Acetyl CoA stokes the furnace. 1
Figure 6.9B_s1 Acetyl CoA CoA CoA 2 carbons enter cycle Oxaloacetate 1 Citric Acid Cycle Figure 6.9B_s1 A closer look at the citric acid cycle (step 1) Step Acetyl CoA stokes the furnace. 1 56

Figure 6.9B_s2 Acetyl CoA CoA CoA 2 carbons enter cycle Oxaloacetate 1 Citrate NAD NADH H 2 Citric Acid Cycle CO2 leaves cycle Alpha-ketoglutarate Figure 6.9B_s2 A closer look at the citric acid cycle (step 2) 3 CO2 leaves cycle NAD ADP P NADH H Step Acetyl CoA stokes the furnace. 1 Steps – NADH, ATP, and CO2 are generated during redox reactions. 2 3 ATP 57

Figure 6.9B_s3 Acetyl CoA CoA CoA 2 carbons enter cycle Oxaloacetate 1 Citrate NADH H NAD 5 NAD NADH H 2 Citric Acid Cycle Malate CO2 leaves cycle FADH2 Alpha-ketoglutarate Figure 6.9B_s3 A closer look at the citric acid cycle (step 3) 4 3 FAD CO2 leaves cycle NAD Succinate ADP P NADH H Step Acetyl CoA stokes the furnace. 1 Steps – NADH, ATP, and CO2 are generated during redox reactions. 2 3 Steps – Further redox reactions generate FADH2 and more NADH. 4 5 ATP 58

6.10 Most ATP production occurs by oxidative phosphorylation
involves electron transport and chemiosmosis and requires an adequate supply of oxygen. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips 1. The production of NADH through glycolysis and the Krebs cycle, as compared to the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have value to be cashed in by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the electron transport cashier. 2. As you relate the structure of the inner mitochondrial membrane to its functions, challenge students to explain the adaptive advantage of the many folds of this inner membrane (see Figure 6.6). (These folds greatly increase the surface area available for the associated reactions). 3. The authors develop an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the inner and outer mitochondrial membranes, like a dam holding back water. As the hydrogen ions move down their concentration gradient, they “spin” the ATP synthase, which helps generate ATP. In a dam, water rushing downhill turns giant turbines, which generate electricity. © 2012 Pearson Education, Inc. 59

6.10 Most ATP production occurs by oxidative phosphorylation
Electrons from NADH and FADH2 travel down the electron transport chain to O2. Oxygen picks up H+ to form water. Energy released by these redox reactions is used to pump H+ from the mitochondrial matrix into the intermembrane space. In chemiosmosis, the H+ diffuses back across the inner membrane through ATP synthase complexes, driving the synthesis of ATP. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips 1. The production of NADH through glycolysis and the Krebs cycle, as compared to the direct production of ATP, can get confusing for students. Help students understand that NADH molecules have value to be cashed in by the electron transport chain. The NADH can therefore be thought of as casino chips, accumulated along the way to be cashed in at the electron transport cashier. 2. As you relate the structure of the inner mitochondrial membrane to its functions, challenge students to explain the adaptive advantage of the many folds of this inner membrane (see Figure 6.6). (These folds greatly increase the surface area available for the associated reactions). 3. The authors develop an analogy between the function of the inner mitochondrial membrane and a dam. A reservoir of hydrogen ions is built up between the inner and outer mitochondrial membranes, like a dam holding back water. As the hydrogen ions move down their concentration gradient, they “spin” the ATP synthase, which helps generate ATP. In a dam, water rushing downhill turns giant turbines, which generate electricity. © 2012 Pearson Education, Inc. 60

Figure 6.10 H H H H H Intermem- brane space H Mobile electron carriers H Protein complex of electron carriers H H ATP synthase III IV I Inner mitochondrial membrane II Electron flow FADH2 FAD 1 2 2 H NADH NAD O2 H2O Mito- chondrial matrix H Figure 6.10 Oxidative phosphorylation: electron transport and chemiosmosis in a mitochondrion ADP P ATP H Electron Transport Chain Chemiosmosis Oxidative Phosphorylation 61

Mobile electron carriers H Protein complex of electron carriers H H
Figure 6.10_1 H H H H H H Mobile electron carriers H Protein complex of electron carriers H H ATP synthase III IV I II FADH2 FAD Electron flow 2 1 2 H O2 NADH H2O NAD H Figure 6.10_1 Oxidative phosphorylation: electron transport and chemiosmosis in a mitochondrion ADP P ATP H Electron Transport Chain Chemiosmosis Oxidative Phosphorylation 62

6.11 CONNECTION: Interrupting cellular respiration can have both harmful and beneficial effects
Three categories of cellular poisons obstruct the process of oxidative phosphorylation. These poisons block the electron transport chain (for example, rotenone, cyanide, and carbon monoxide), inhibit ATP synthase (for example, the antibiotic oligomycin), or make the membrane leaky to hydrogen ions (called uncouplers, examples include dinitrophenol). Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips Module 6.11 explores the many points in cellular respiration where poisons may produce their deadly effects. Like any complex process, such as an engine of a car or the cooperation of athletes on a team, the results depend upon the proper functioning of each part. Poisons can stop a metabolic pathway by disrupting a single step in the process. © 2012 Pearson Education, Inc. 63

Cyanide, carbon monoxide
Figure 6.11 Rotenone Cyanide, carbon monoxide Oligomycin H H H ATP synthase H H H H DNP FADH2 FAD Figure 6.11 How some poisons affect the electron transport chain and chemiosmosis 2 1 O2 2 H NADH NAD H H2O ADP P ATP 64

Brown fat is a special type of tissue associated with the generation of heat and more abundant in hibernating mammals and newborn infants. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips Module 6.11 explores the many points in cellular respiration where poisons may produce their deadly effects. Like any complex process, such as an engine of a car or the cooperation of athletes on a team, the results depend upon the proper functioning of each part. Poisons can stop a metabolic pathway by disrupting a single step in the process. © 2012 Pearson Education, Inc. 65

In brown fat, the cells are packed full of mitochondria, the inner mitochondrial membrane contains an uncoupling protein, which allows H+ to flow back down its concentration gradient without generating ATP, and ongoing oxidation of stored fats generates additional heat. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips Module 6.11 explores the many points in cellular respiration where poisons may produce their deadly effects. Like any complex process, such as an engine of a car or the cooperation of athletes on a team, the results depend upon the proper functioning of each part. Poisons can stop a metabolic pathway by disrupting a single step in the process. © 2012 Pearson Education, Inc. 66

6.12 Review: Each molecule of glucose yields many molecules of ATP
Recall that the energy payoff of cellular respiration involves glycolysis, alteration of pyruvate, the citric acid cycle, and oxidative phosphorylation. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips Students should be reminded that the ATP yield of up to 32 ATP per glucose molecule is only a potential. The complex chemistry of aerobic metabolism can yield this amount only under ideal conditions, when every substrate and enzyme is immediately available. Such circumstances may occur only rarely in a working cell. © 2012 Pearson Education, Inc. 67

6.12 Review: Each molecule of glucose yields many molecules of ATP
The total yield is about 32 ATP molecules per glucose molecule. This is about 34% of the potential energy of a glucose molecule. In addition, water and CO2 are produced. Student Misconceptions and Concerns 1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction. 2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration. 3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night). Teaching Tips Students should be reminded that the ATP yield of up to 32 ATP per glucose molecule is only a potential. The complex chemistry of aerobic metabolism can yield this amount only under ideal conditions, when every substrate and enzyme is immediately available. Such circumstances may occur only rarely in a working cell. © 2012 Pearson Education, Inc. 68

   CYTOPLASM Electron shuttles across membrane Mitochondrion 2 NADH
Figure 6.12 CYTOPLASM Electron shuttles across membrane Mitochondrion 2 NADH 2 or NADH 2 FADH2 6 2 2 NADH NADH FADH2 Pyruvate Oxidation 2 Acetyl CoA Glycolysis Oxidative Phosphorylation (electron transport and chemiosmosis) 2 Pyruvate Citric Acid Cycle Glucose Maximum per glucose: Figure 6.12 An estimated tally of the ATP produced by substrate-level and oxidative phosphorylation in cellular respiration ATP  2 ATP  2 about  28 ATP About ATP 32 by substrate-level phosphorylation by substrate-level phosphorylation by oxidative phosphorylation 69

FERMENTATION: ANAEROBIC HARVESTING OF ENERGY

6.13 Fermentation enables cells to produce ATP without oxygen
Fermentation is a way of harvesting chemical energy that does not require oxygen. Fermentation takes advantage of glycolysis, produces two ATP molecules per glucose, and reduces NAD+ to NADH. The trick of fermentation is to provide an anaerobic path for recycling NADH back to NAD+. Student Misconceptions and Concerns Students may expect that fermentation will produce alcohol and maybe even carbon dioxide. Take the time to clarify the different possible products of fermentation and correct this general misconception. Teaching Tips 1. The text notes that some microbes are useful in the dairy industry because they produce lactic acid. However, the impact of acids on milk may not be obvious to many students. Consider a simple demonstration mixing about equal portions of milk (skim or 2%) with some acid (vinegar will work). Notice the accumulation of strands of milk curd (protein) on the side of the container and stirring device. 2. Dry wines are produced when the yeast cells use up all or most of the sugar available. Sweet wines result when the alcohol accumulates enough to inhibit fermentation before the sugar is depleted. 3. Exposing fermenting yeast to oxygen will slow or stop the process, because the yeast will switch back to aerobic respiration. When fermentation is rapid, the carbon dioxide produced drives away the oxygen immediately above the wine. However, as fermentation slows down, the wine must be sealed to prevent oxygen exposure and permit the fermentation process to finish. © 2012 Pearson Education, Inc. 71

Your muscle cells and certain bacteria can oxidize NADH through lactic acid fermentation, in which NADH is oxidized to NAD+ and pyruvate is reduced to lactate. Student Misconceptions and Concerns Students may expect that fermentation will produce alcohol and maybe even carbon dioxide. Take the time to clarify the different possible products of fermentation and correct this general misconception. Teaching Tips 1. The text notes that some microbes are useful in the dairy industry because they produce lactic acid. However, the impact of acids on milk may not be obvious to many students. Consider a simple demonstration mixing about equal portions of milk (skim or 2%) with some acid (vinegar will work). Notice the accumulation of strands of milk curd (protein) on the side of the container and stirring device. 2. Dry wines are produced when the yeast cells use up all or most of the sugar available. Sweet wines result when the alcohol accumulates enough to inhibit fermentation before the sugar is depleted. 3. Exposing fermenting yeast to oxygen will slow or stop the process, because the yeast will switch back to aerobic respiration. When fermentation is rapid, the carbon dioxide produced drives away the oxygen immediately above the wine. However, as fermentation slows down, the wine must be sealed to prevent oxygen exposure and permit the fermentation process to finish. Animation: Fermentation Overview © 2012 Pearson Education, Inc. 72

Lactate is carried by the blood to the liver, where it is converted back to pyruvate and oxidized in the mitochondria of liver cells. The dairy industry uses lactic acid fermentation by bacteria to make cheese and yogurt. Other types of microbial fermentation turn soybeans into soy sauce and cabbage into sauerkraut. Student Misconceptions and Concerns Students may expect that fermentation will produce alcohol and maybe even carbon dioxide. Take the time to clarify the different possible products of fermentation and correct this general misconception. Teaching Tips 1. The text notes that some microbes are useful in the dairy industry because they produce lactic acid. However, the impact of acids on milk may not be obvious to many students. Consider a simple demonstration mixing about equal portions of milk (skim or 2%) with some acid (vinegar will work). Notice the accumulation of strands of milk curd (protein) on the side of the container and stirring device. 2. Dry wines are produced when the yeast cells use up all or most of the sugar available. Sweet wines result when the alcohol accumulates enough to inhibit fermentation before the sugar is depleted. 3. Exposing fermenting yeast to oxygen will slow or stop the process, because the yeast will switch back to aerobic respiration. When fermentation is rapid, the carbon dioxide produced drives away the oxygen immediately above the wine. However, as fermentation slows down, the wine must be sealed to prevent oxygen exposure and permit the fermentation process to finish. © 2012 Pearson Education, Inc. 73

Glucose 2 ADP 2 NAD 2 P Glycolysis 2 ATP 2 NADH 2 Pyruvate 2 NADH
Figure 6.13A Glucose 2 ADP 2 NAD 2 P Glycolysis 2 ATP 2 NADH 2 Pyruvate 2 NADH Figure 6.13A Lactic acid fermentation: NAD+ is regenerated as pyruvate is reduced to lactate. 2 NAD 2 Lactate 74

The baking and winemaking industries have used alcohol fermentation for thousands of years. In this process yeasts (single-celled fungi) oxidize NADH back to NAD+ and convert pyruvate to CO2 and ethanol. Student Misconceptions and Concerns Students may expect that fermentation will produce alcohol and maybe even carbon dioxide. Take the time to clarify the different possible products of fermentation and correct this general misconception. Teaching Tips 1. The text notes that some microbes are useful in the dairy industry because they produce lactic acid. However, the impact of acids on milk may not be obvious to many students. Consider a simple demonstration mixing about equal portions of milk (skim or 2%) with some acid (vinegar will work). Notice the accumulation of strands of milk curd (protein) on the side of the container and stirring device. 2. Dry wines are produced when the yeast cells use up all or most of the sugar available. Sweet wines result when the alcohol accumulates enough to inhibit fermentation before the sugar is depleted. 3. Exposing fermenting yeast to oxygen will slow or stop the process, because the yeast will switch back to aerobic respiration. When fermentation is rapid, the carbon dioxide produced drives away the oxygen immediately above the wine. However, as fermentation slows down, the wine must be sealed to prevent oxygen exposure and permit the fermentation process to finish. © 2012 Pearson Education, Inc. 75

Glucose 2 ADP 2 NAD Glycolysis 2 P 2 ATP 2 NADH 2 Pyruvate 2 NADH
Figure 6.13B Glucose 2 ADP 2 NAD 2 P Glycolysis 2 ATP 2 NADH 2 Pyruvate Figure 6.13B Alchohol fermentation: NAD is regenerated as pyruvate is broken down to CO2 and ethanol. 2 NADH 2 CO2 2 NAD 2 Ethanol 76

Obligate anaerobes are poisoned by oxygen, requiring anaerobic conditions, and live in stagnant ponds and deep soils. Facultative anaerobes include yeasts and many bacteria, and can make ATP by fermentation or oxidative phosphorylation. Student Misconceptions and Concerns Students may expect that fermentation will produce alcohol and maybe even carbon dioxide. Take the time to clarify the different possible products of fermentation and correct this general misconception. Teaching Tips 1. The text notes that some microbes are useful in the dairy industry because they produce lactic acid. However, the impact of acids on milk may not be obvious to many students. Consider a simple demonstration mixing about equal portions of milk (skim or 2%) with some acid (vinegar will work). Notice the accumulation of strands of milk curd (protein) on the side of the container and stirring device. 2. Dry wines are produced when the yeast cells use up all or most of the sugar available. Sweet wines result when the alcohol accumulates enough to inhibit fermentation before the sugar is depleted. 3. Exposing fermenting yeast to oxygen will slow or stop the process, because the yeast will switch back to aerobic respiration. When fermentation is rapid, the carbon dioxide produced drives away the oxygen immediately above the wine. However, as fermentation slows down, the wine must be sealed to prevent oxygen exposure and permit the fermentation process to finish. © 2012 Pearson Education, Inc. 77

Figure 6.13C_1 Figure 6.13C_1 Wine barrels 78

Figure 6.13C_2 Figure 6.13C_2 Beer fermentation vats 79

6.14 EVOLUTION CONNECTION: Glycolysis evolved early in the history of life on Earth
Glycolysis is the universal energy-harvesting process of life. The role of glycolysis in fermentation and respiration dates back to life long before oxygen was present, when only prokaryotes inhabited the Earth, about 3.5 billion years ago. Teaching Tips The widespread occurrence of glycolysis, which takes place in the cytosol and independent of organelles, suggests that this process had an early evolutionary origin. Since atmospheric oxygen was not available in significant amounts during the early stages of Earth’s history, and glycolysis does not require oxygen, it is likely that this chemical pathway was used by the prokaryotes in existence at that time. Students focused on the evolution of large, readily apparent structures such as wings and teeth may have never considered the evolution of cellular chemistry. © 2012 Pearson Education, Inc. 80

6.14 EVOLUTION CONNECTION: Glycolysis evolved early in the history of life on Earth
The ancient history of glycolysis is supported by its occurrence in all the domains of life and location within the cell, using pathways that do not involve any membrane-bounded organelles. Teaching Tips The widespread occurrence of glycolysis, which takes place in the cytosol and independent of organelles, suggests that this process had an early evolutionary origin. Since atmospheric oxygen was not available in significant amounts during the early stages of Earth’s history, and glycolysis does not require oxygen, it is likely that this chemical pathway was used by the prokaryotes in existence at that time. Students focused on the evolution of large, readily apparent structures such as wings and teeth may have never considered the evolution of cellular chemistry. © 2012 Pearson Education, Inc. 81

CONNECTIONS BETWEEN METABOLIC PATHWAYS

6.15 Cells use many kinds of organic molecules as fuel for cellular respiration
Although glucose is considered to be the primary source of sugar for respiration and fermentation, ATP is generated using carbohydrates, fats, and proteins. 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). 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. Figure 6.15 is an important visual synthesis of the diverse fuels that can enter into cellular respiration and the various stages of this process. Figures such as this can serve as a visual anchor to integrate the many aspects of this chapter. 3. The final modules in this chapter may raise questions about obesity and proper diet. The Centers for Disease Control and Prevention website, discusses many aspects of nutrition, obesity, and general physical fitness and is a useful reference for teachers and students. © 2012 Pearson Education, Inc. 83

6.15 Cells use many kinds of organic molecules as fuel for cellular respiration
Fats make excellent cellular fuel because they contain many hydrogen atoms and thus many energy-rich electrons and yield more than twice as much ATP per gram than a gram of carbohydrate or protein. 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). 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. Figure 6.15 is an important visual synthesis of the diverse fuels that can enter into cellular respiration and the various stages of this process. Figures such as this can serve as a visual anchor to integrate the many aspects of this chapter. 3. The final modules in this chapter may raise questions about obesity and proper diet. The Centers for Disease Control and Prevention website, discusses many aspects of nutrition, obesity, and general physical fitness and is a useful reference for teachers and students. © 2012 Pearson Education, Inc. 84

Pyruvate Oxidation Acetyl CoA Oxidative Phosphorylation
Figure 6.15 Food, such as peanuts Carbohydrates Fats Proteins Sugars Glycerol Fatty acids Amino acids Amino groups Figure 6.15 Pathways that break down various food molecules Citric Acid Cycle Pyruvate Oxidation Acetyl CoA Oxidative Phosphorylation Glucose G3P Pyruvate Glycolysis ATP 85

Pyruvate Oxidation Acetyl CoA Oxidative Phosphorylation
Figure 6.15_1 Food Carbohydrates Fats Proteins Sugars Glycerol Fatty acids Amino acids Amino groups Figure 6.15_1 Pathways that break down various food molecules Citric Acid Cycle Pyruvate Oxidation Acetyl CoA Oxidative Phosphorylation Glucose G3P Pyruvate Glycolysis ATP 86

6.16 Food molecules provide raw materials for biosynthesis
Cells use intermediates from cellular respiration for the biosynthesis of other organic molecules. Student Misconceptions and Concerns Some students may only view nutrients as sources of calories. As noted in Module 6.16, the monomers of many nutrients are recycled into synthetic pathways of organic molecules. Teaching Tips The final modules in this chapter may raise questions about obesity and proper diet. The Centers for Disease Control and Prevention website, discusses many aspects of nutrition, obesity, and general physical fitness and is a useful reference for teachers and students. © 2012 Pearson Education, Inc. 87

Pyruvate Oxidation Acetyl CoA
Figure 6.16 ATP needed to drive biosynthesis ATP Citric Acid Cycle Pyruvate Oxidation Acetyl CoA Glucose Synthesis Pyruvate G3P Glucose Amino groups Amino acids Fatty acids Glycerol Sugars Proteins Fats Carbohydrates Figure 6.16 Biosynthesis of large organic molecules from intermediates of cellular respiration Cells, tissues, organisms 88

Pyruvate Oxidation Acetyl CoA
Figure 6.16_1 ATP needed to drive biosynthesis ATP Citric Acid Cycle Pyruvate Oxidation Acetyl CoA Glucose Synthesis Pyruvate G3P Glucose Amino groups Amino acids Fatty acids Glycerol Sugars Figure 6.16_1 Biosynthesis of large organic molecules from intermediates of cellular respiration Proteins Fats Carbohydrates Cells, tissues, organisms 89

Figure 6.16_2 Figure 6.16_2 Biosynthesis of large organic molecules from intermediates of cellular respiration 90

6.16 Food molecules provide raw materials for biosynthesis
Metabolic pathways are often regulated by feedback inhibition in which an accumulation of product suppresses the process that produces the product. Student Misconceptions and Concerns Some students may only view nutrients as sources of calories. As noted in Module 6.16, the monomers of many nutrients are recycled into synthetic pathways of organic molecules. Teaching Tips The final modules in this chapter may raise questions about obesity and proper diet. The Centers for Disease Control and Prevention website, discusses many aspects of nutrition, obesity, and general physical fitness and is a useful reference for teachers and students. © 2012 Pearson Education, Inc. 91

You should now be able to
Compare the processes and locations of cellular respiration and photosynthesis. Explain how breathing and cellular respiration are related. Provide the overall chemical equation for cellular respiration. Explain how the human body uses its daily supply of ATP. © 2012 Pearson Education, Inc. 92

Explain how the energy in a glucose molecule is released during cellular respiration. Explain how redox reactions are used in cellular respiration. Describe the general roles of dehydrogenase, NADH, and the electron transport chain in cellular respiration. Compare the reactants, products, and energy yield of the three stages of cellular respiration. © 2012 Pearson Education, Inc. 93

Explain how rotenone, cyanide, carbon monoxide, oligomycin, and uncouplers interrupt critical events in cellular respiration. Compare the reactants, products, and energy yield of alcohol and lactic acid fermentation. Distinguish between strict anaerobes and facultative anaerobes. Explain how carbohydrates, fats, and proteins are used as fuel for cellular respiration. © 2012 Pearson Education, Inc. 94

Electrons carried by NADH Citric Acid Cycle Pyruvate Oxidation
Figure 6.UN01 CYTOPLASM NADH Mitochondrion Electrons carried by NADH NADH FADH2 Glycolysis Citric Acid Cycle Oxidative Phosphorylation (electron transport and chemiosmosis) Pyruvate Oxidation Glucose Pyruvate Figure 6.UN01 Reviewing the Concepts, 6.6 Substrate- level phosphorylation Substrate- level phosphorylation ATP Oxidative phosphorylation ATP ATP 95

glucose and organic fuels H diffuse through ATP synthase
Figure 6.UN02 Cellular respiration generates has three stages oxidizes uses glucose and organic fuels (a) produce some (b) produces many (d) energy for to pull electrons down to (c) cellular work (f) by a process called uses (g) Figure 6.UN02 Connecting the Concepts, question 1 H diffuse through ATP synthase chemiosmosis (e) uses pumps H to create H gradient 96

0.3 0.3 0.2 0.1 0.2 0.2 Color intensity 0.1 0.1 0.3 a. Time b. Time c.
Figure 6.UN03 0.3 0.3 0.2 0.1 0.2 0.2 Color intensity 0.1 0.1 0.3 Figure 6.UN03 Applying the Concepts, question 15 a. Time b. Time c. Time 97

How Cells Harvest Chemical Energy

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