1. Chapter 7: Cellular Pathways That Harvest Chemical Energy CHAPTER 7 Cellular Pathways That Harvest Chemical Energy

2. Chapter 7: Cellular Pathways That Harvest Chemical Energy Obtaining Energy and Electrons from Glucose Obtaining Energy and Electrons from Glucose An Overview: Releasing Energy from Glucose An Overview: Releasing Energy from Glucose Glycolysis: From Glucose to Pyruvate Glycolysis: From Glucose to Pyruvate Oxidation Pyruvate Oxidation The Citric Acid Cycle The Citric Acid Cycle

3. Chapter 7: Cellular Pathways That Harvest Chemical Energy The Respiratory Chain: Electrons, Proton Pumping, and ATP The Respiratory Chain: Electrons, Proton Pumping, and ATP Fermentation: ATP from Glucose, without O 2 Fermentation: ATP from Glucose, without O 2 Contrasting Energy Yields Contrasting Energy Yields Metabolic Pathways Metabolic Pathways Regulating Energy Pathways Regulating Energy Pathways

4. Chapter 7: Cellular Pathways That Harvest Chemical Energy Cellular Pathways Metabolic pathways occur in small steps, each catalyzed by a specific enzyme.Metabolic pathways occur in small steps, each catalyzed by a specific enzyme.4

5. Chapter 7: Cellular Pathways That Harvest Chemical Energy Cellular Pathways Metabolic pathways are often compartmentalized and are highly regulated.Metabolic pathways are often compartmentalized and are highly regulated.5

6. Chapter 7: Cellular Pathways That Harvest Chemical Energy Obtaining Energy and Electrons from Glucose When glucose burns, energy is released as heat and light:When glucose burns, energy is released as heat and light: C 6 H 12 O 6 + 6 O 2  6 CO 2 + 6 H 2 0 + energy The same equation applies to the metabolism of glucose by cells, but the reaction is accomplished in many separate steps so that the energy can be captured as ATP. Review Figure 7.1 7.1 6

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8. Chapter 7: Cellular Pathways That Harvest Chemical Energy Obtaining Energy and Electrons from Glucose As a material is oxidized, the electrons it loses transfer to another material, which is thereby reduced.As a material is oxidized, the electrons it loses transfer to another material, which is thereby reduced. Such redox reactions transfer a lot of energy.Such redox reactions transfer a lot of energy. Much of the energy liberated by the oxidation of the reducing agent is captured in the reduction of the oxidizing agent.Much of the energy liberated by the oxidation of the reducing agent is captured in the reduction of the oxidizing agent. Review Figure 7.2Review Figure 7.27.2 8

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10. Chapter 7: Cellular Pathways That Harvest Chemical Energy Obtaining Energy and Electrons from Glucose The coenzyme NAD is a key electron carrier in biological redox reactions.The coenzyme NAD is a key electron carrier in biological redox reactions. It exists in two forms, one oxidized (NAD + ) and the other reduced (NADH + H + ).It exists in two forms, one oxidized (NAD + ) and the other reduced (NADH + H + ). Review Figures 7.3, 7.4 7.37.47.37.410

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13. Chapter 7: Cellular Pathways That Harvest Chemical Energy An Overview: Releasing Energy from Glucose Glycolysis operates in the presence or absence of O 2.Glycolysis operates in the presence or absence of O 2. Under aerobic conditions, cellular respiration continues the breakdown process.Under aerobic conditions, cellular respiration continues the breakdown process. Review Figure 7.5 7.5 13

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16. Chapter 7: Cellular Pathways That Harvest Chemical Energy An Overview: Releasing Energy from Glucose Pyruvate oxidation and the citric acid cycle produce CO 2 and hydrogen atoms carried by NADH and FADH 2.Pyruvate oxidation and the citric acid cycle produce CO 2 and hydrogen atoms carried by NADH and FADH 2. The respiratory chain combines the hydrogens with O 2, releasing enough energy for ATP synthesis.The respiratory chain combines the hydrogens with O 2, releasing enough energy for ATP synthesis. Review Figure 7.5a 7.5 16

17. Chapter 7: Cellular Pathways That Harvest Chemical Energy An Overview: Releasing Energy from Glucose In some cells under anaerobic conditions, pyruvate can be reduced by NADH to form lactate and regenerate the NAD needed to sustain glycolysis.In some cells under anaerobic conditions, pyruvate can be reduced by NADH to form lactate and regenerate the NAD needed to sustain glycolysis. Review Figure 7.5b 7.5 17

18. Chapter 7: Cellular Pathways That Harvest Chemical Energy An Overview: Releasing Energy from Glucose In eukaryotes, glycolysis and fermentation occur in the cytoplasm outside of the mitochondria; pyruvate oxidation, the citric acid cycle, and the respiratory chain operate in association with mitochondria.In eukaryotes, glycolysis and fermentation occur in the cytoplasm outside of the mitochondria; pyruvate oxidation, the citric acid cycle, and the respiratory chain operate in association with mitochondria. In prokaryotes, glycolysis, fermentation, and the citric acid cycle take place in the cytoplasm; and pyruvate oxidation and the respiratory chain operate in association with the plasma membrane.In prokaryotes, glycolysis, fermentation, and the citric acid cycle take place in the cytoplasm; and pyruvate oxidation and the respiratory chain operate in association with the plasma membrane. Review Table 7.1 7.1 18

19. Chapter 7: Cellular Pathways That Harvest Chemical Energy Table 7.1 table 07-01.jpg

20. Chapter 7: Cellular Pathways That Harvest Chemical Energy Glycolysis: From Glucose to Pyruvate Glycolysis is a pathway of ten enzyme- catalyzed reactions located in the cytoplasm.Glycolysis is a pathway of ten enzyme- catalyzed reactions located in the cytoplasm. It provides starting materials for both cellular respiration and fermentation.It provides starting materials for both cellular respiration and fermentation. Review Figure 7.6 7.6 20

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22. Chapter 7: Cellular Pathways That Harvest Chemical Energy Glycolysis: From Glucose to Pyruvate Glycolysis uses two ATPs for activation energy & yields two PGAL’s.Glycolysis uses two ATPs for activation energy & yields two PGAL’s. Two NADH molecules are produced, and four ATP molecules are generated.Two NADH molecules are produced, and four ATP molecules are generated. Two pyruvates are produced for each glucose molecule.Two pyruvates are produced for each glucose molecule. Review Figures 7.6, 7.7 7.67.77.67.722

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26. Chapter 7: Cellular Pathways That Harvest Chemical Energy Pyruvate Oxidation The pyruvate dehydrogenase complex catalyzes three reactions: The pyruvate dehydrogenase complex catalyzes three reactions:  Pyruvate is oxidized to the acetyl group, releasing one CO 2 molecule and energy;  Some of this energy is captured when NAD + is reduced to NADH + H + ;  The remaining energy is captured when the acetyl group combines with coenzyme A, yielding acetyl CoA. Review Figure 7.8, 7.9a 7.8 26

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28. Chapter 7: Cellular Pathways That Harvest Chemical Energy The Citric Acid Cycle The energy in acetyl CoA drives the reaction of acetate with oxaloacetate to produce citrate.The energy in acetyl CoA drives the reaction of acetate with oxaloacetate to produce citrate. The citric acid cycle is a series of reactions in which citrate is oxidized and oxaloacetate regenerated.The citric acid cycle is a series of reactions in which citrate is oxidized and oxaloacetate regenerated. It produces two CO 2, one FADH 2, three NADH, and one ATP for each acetyl CoA.It produces two CO 2, one FADH 2, three NADH, and one ATP for each acetyl CoA. Review Figures 7.9b, 7.10 7.97.107.97.1028

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32. Chapter 7: Cellular Pathways That Harvest Chemical Energy The Respiratory Chain: Electrons, Proton Pumping, and ATP NADH + H + and FADH 2 are oxidized by the respiratory chain, regenerating NAD + and FAD. NADH + H + and FADH 2 are oxidized by the respiratory chain, regenerating NAD + and FAD. The enzymes and electron carriers of the chain are part of the inner mitochondrial membrane.The enzymes and electron carriers of the chain are part of the inner mitochondrial membrane. O 2 is the final acceptor of electrons and protons, forming H 2 O.O 2 is the final acceptor of electrons and protons, forming H 2 O. Review Figures 7.11, 7.12 7.117.127.117.1232

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35. Chapter 7: Cellular Pathways That Harvest Chemical Energy The Respiratory Chain: Electrons, Proton Pumping, and ATP The chemiosmotic mechanism couples proton transport to ADP oxidative phosphorylation.The chemiosmotic mechanism couples proton transport to ADP oxidative phosphorylation. As electrons move along the cytochromes, they lose energyAs electrons move along the cytochromes, they lose energy Proton pumps actively transport H + out of the mitochondrial matrix, establishing a gradient of proton concentration and electric charge—the proton-motive force.Proton pumps actively transport H + out of the mitochondrial matrix, establishing a gradient of proton concentration and electric charge—the proton-motive force. Review Figure 7.13 7.13 35

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38. Chapter 7: Cellular Pathways That Harvest Chemical Energy The Respiratory Chain: Electrons, Proton Pumping, and ATP The proton-motive force causes protons to diffuse back into the mitochondrial interior through the membrane channel protein ATP synthase, which couples that diffusion to the production of ATP.The proton-motive force causes protons to diffuse back into the mitochondrial interior through the membrane channel protein ATP synthase, which couples that diffusion to the production of ATP. Review Figure 7.14 7.14 38

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41. Chapter 7: Cellular Pathways That Harvest Chemical Energy Fermentation: ATP from Glucose, without O 2 Many organisms and some cells live without O 2, deriving energy from glycolysis and fermentation. Many organisms and some cells live without O 2, deriving energy from glycolysis and fermentation. Together, these pathways partly oxidize glucose and generate energy-containing products.Together, these pathways partly oxidize glucose and generate energy-containing products. Fermentation reactions anaerobically oxidize the NADH + H + produced in glycolysis.Fermentation reactions anaerobically oxidize the NADH + H + produced in glycolysis. Review Figures 7.15, 7.16 7.157.167.157.1641

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44. Chapter 7: Cellular Pathways That Harvest Chemical Energy Contrasting Energy Yields For each molecule of glucose used, fermentation yields 2 molecules of ATP. For each molecule of glucose used, fermentation yields 2 molecules of ATP. In contrast, aerobic respiration yields up to 36.In contrast, aerobic respiration yields up to 36. Review Figure 7.17 7.17 44

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47. Chapter 7: Cellular Pathways That Harvest Chemical Energy Metabolic Pathways Catabolic pathways feed into the respiratory pathways.Catabolic pathways feed into the respiratory pathways. Polysaccharides are broken down into glucose, which enters glycolysis.Polysaccharides are broken down into glucose, which enters glycolysis. Glycerol from fats also enters glycolysis, and acetyl CoA from fatty acids enters the citric acid cycle.Glycerol from fats also enters glycolysis, and acetyl CoA from fatty acids enters the citric acid cycle. Proteins enter glycolysis and the citric acid cycle via amino acids.Proteins enter glycolysis and the citric acid cycle via amino acids. Review Figures 7.18, 7.19 7.187.197.187.1947

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50. Chapter 7: Cellular Pathways That Harvest Chemical Energy Metabolic Pathways Anabolic pathways use intermediate components of respiratory metabolism to synthesize fats, amino acids, and other molecules.Anabolic pathways use intermediate components of respiratory metabolism to synthesize fats, amino acids, and other molecules. Review Figures 7.18, 7.19 7.187.197.187.1950

51. Chapter 7: Cellular Pathways That Harvest Chemical Energy Regulating Energy Pathways The rates of glycolysis and the citric acid cycle are regulated by the actions of ATP, ADP, NAD +, or NADH + H + on allosteric enzymes. The rates of glycolysis and the citric acid cycle are regulated by the actions of ATP, ADP, NAD +, or NADH + H + on allosteric enzymes.51

52. Chapter 7: Cellular Pathways That Harvest Chemical Energy Regulating Energy Pathways Inhibition of the glycolytic enzyme phosphofructokinase by abundant ATP slows glycolysis.Inhibition of the glycolytic enzyme phosphofructokinase by abundant ATP slows glycolysis. ADP activates this enzyme.ADP activates this enzyme. The citric acid cycle enzyme isocitrate dehydrogenase is inhibited by ATP and NADH and activated by ADP and NAD +.The citric acid cycle enzyme isocitrate dehydrogenase is inhibited by ATP and NADH and activated by ADP and NAD +. Review Figures 7.20, 7.21 7.207.217.207.2152

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