Pathways that Harvest and Store Chemical Energy

1. 6 Pathways that Harvest andStore Chemical Energy

2. Chapter 6 Pathways that Harvest and Store Chemical Energy • Key Concepts • 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism • 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy • 6.3 Carbohydrate Catabolism in the Absence of Oxygen Releases a Small Amount of Energy

3. Chapter 6 Pathways that Harvest and Store Chemical Energy 6.4 Catabolic and Anabolic Pathways Are Integrated 6.5 During Photosynthesis, Light Energy Is Converted to Chemical Energy 6.6 Photosynthetic Organisms Use Chemical Energy to Convert CO2 to Carbohydrates

4. Chapter 6 Opening Question Why does fresh air inhibit the formation of alcohol by yeast cells?

5. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism Energy is stored in chemical bonds and can be released and transformed by metabolic pathways. Chemical energy available to do work is termed free energy (G).

6. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism • Five principles governing metabolic pathways: • Chemical transformations occur in a series of intermediate reactions that form a metabolic pathway. • Each reaction is catalyzed by a specific enzyme. • Most metabolic pathways are similar in all organisms.

7. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism In eukaryotes, many metabolic pathways occur inside specific organelles. Each metabolic pathway is controlled by enzymes that can be inhibited or activated.

8. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism In cells, energy-transforming reactions are often coupled: An energy-releasing (exergonic) reaction is coupled to an energy-requiring (endergonic) reaction.

9. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism Adenosine triphosphate (ATP) is a kind of “energy currency” in cells. Energy released by exergonic reactions is stored in the bonds of ATP. When ATP is hydrolyzed, free energy is released to drive endergonic reactions.

10. Figure 6.1 The Concept of Coupling Reactions

11. Figure 6.2 ATP

12. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism Hydrolysis of ATP is exergonic: ΔG is about –7.3 kcal

13. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism Free energy of the bond between phosphate groups is much higher than the energy of the O—H bond that forms after hydrolysis. text art pg 102 here (1st one, in left-hand column)

14. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism Phosphate groups are negatively charged, so energy is required to get them near enough to each other to make the covalent bonds in the ATP molecule. ATP can be formed by substrate-level phosphorylation or oxidative phosphorylation.

15. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism Energy can also be transferred by the transfer of electrons in oxidation–reduction, or redox reactions. Reduction is the gain of one or more electrons. • Oxidation is the loss of one or more electrons.

16. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism Oxidation and reduction always occur together.

17. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism Transfers of hydrogen atoms involve transfers of electrons (H = H+ + e–). When a molecule loses a hydrogen atom, it becomes oxidized.

18. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism The more reduced a molecule is, the more energy is stored in its bonds. Energy is transferred in a redox reaction. Energy in the reducing agent is transferred to the reduced product.

19. Figure 6.3 Oxidation, Reduction, and Energy

20. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism Coenzyme NAD+ is a key electron carrier in redox reactions. NAD+ (oxidized form) NADH (reduced form)

21. Figure 6.4 A NAD+/NADH Is an Electron Carrier in Redox Reactions

22. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism Reduction of NAD+ is highly endergonic: Oxidation of NADH is highly exergonic:

23. Figure 6.4 B NAD+/NADH Is an Electron Carrier in Redox Reactions

24. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism In cells, energy is released in catabolism by oxidation and trapped by reduction of coenzymes such as NADH. • Energy for anabolic processes is supplied by ATP. Oxidative phosphorylation transfers energy from NADH to ATP.

25. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism Oxidative phosphorylation couples oxidation of NADH: with production of ATP:

26. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism The coupling is chemiosmosis—diffusion of protons across a membrane, which drives the synthesis of ATP. Chemiosmosis converts potential energy of a proton gradient across a membrane into the chemical energy in ATP.

27. Figure 6.5 A Chemiosmosis

28. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism ATP synthase—membrane protein with two subunits: F0 is the H+ channel; potential energy of the proton gradient drives the H+ through. F1 has active sites for ATP synthesis.

29. Figure 6.5 B Chemiosmosis

30. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism Chemiosmosis can be demonstrated experimentally. A proton gradient can be introduced artificially in chloroplasts or mitochondria in a test tube. ATP is synthesized if ATP synthase, ADP, and inorganic phosphate are present.

31. Figure 6.6 An Experiment Demonstrates the Chemiosmotic Mechanism

32. Concept 6.1 ATP, Reduced Coenzymes, and Chemiosmosis Play Important Roles in Biological Energy Metabolism Cellular respiration is a major catabolic pathway. Glucose is oxidized: Photosynthesis is a major anabolic pathway. Light energy is converted to chemical energy:

33. Figure 6.7 ATP, Reduced Coenzymes, and Metabolism

34. Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy Cellular Respiration A lot of energy is released when reduced molecules with many C—C and C—H bonds are fully oxidized to CO2. Oxidation occurs in a series of small steps in three pathways: 1. glycolysis 2. pyruvate oxidation 3. citric acid cycle

35. Figure 6.8 Energy Metabolism Occurs in Small Steps

36. Figure 6.9 Energy-Releasing Metabolic Pathways

37. Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy Glycolysis: ten reactions. Takes place in the cytosol. Final products: 2 molecules of pyruvate (pyruvic acid) 2 molecules of ATP 2 molecules of NADH

38. Figure 6.10 Glycolysis Converts Glucose into Pyruvate (Part 1)

39. Figure 6.10 Glycolysis Converts Glucose into Pyruvate (Part 2)

40. Figure 6.10 Glycolysis Converts Glucose into Pyruvate (Part 3)

41. Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy Examples of reaction types common in metabolic pathways: Step 6: Oxidation–reduction Step 7: Substrate-level phosphorylation text art pg 107 here

42. Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy Pyruvate Oxidation: Products: CO2 and acetate; acetate is then bound to coenzyme A (CoA)

43. Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy Citric Acid Cycle: 8 reactions, operates twice for every glucose molecule that enters glycolysis. Starts with Acetyl CoA; acetyl group is oxidized to two CO2. Oxaloacetate is regenerated in the last step.

44. Figure 6.11 The Citric Acid Cycle

45. Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy Final reaction of citric acid cycle:

46. Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy Electron transport/ATP Synthesis: NADH is reoxidized to NAD+ and O2 is reduced to H2O in a series of steps. Respiratory chain—series of redox carrier proteins embedded in the inner mitochondrial membrane. Electron transport—electrons from the oxidation of NADH and FADH2 pass from one carrier to the next in the chain.

47. Figure 6.12 Electron Transport and ATP Synthesis in Mitochondria

48. Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy The oxidation reactions are exergonic; the energy is used to actively transport H+ ions out of the mitochondrial matrix, setting up a proton gradient. ATP synthase in the membrane uses the H+ gradient to synthesize ATP by chemiosmosis.

49. Concept 6.2 Carbohydrate Catabolism in the Presence of Oxygen Releases a Large Amount of Energy About 32 molecules of ATP are produced for each fully oxidized glucose. The role of O2: most of the ATP produced is formed by oxidative phosphorylation, which is due to the reoxidation of NADH.

50. Concept 6.3 Carbohydrate Catabolism in the Absence of Oxygen Releases a Small Amount of Energy Under anaerobic conditions, NADH is reoxidized by fermentation. There are many different types of fermentation, but all operate to regenerate NAD+. The overall yield of ATP is only two—the ATP made in glycolysis.