How Cells make ATP: Energy-Releasing Pathways

1. How Cells make ATP:Energy-Releasing Pathways Chapter 8

2. Learning Objective 1 • In aerobic respiration, which reactant is oxidized and which is reduced?

3. Aerobic Respiration • A catabolic process • fuel (glucose) broken down to carbon dioxide and water • Redox reactions • transfer electrons from glucose (oxidized) • to oxygen (reduced) • Energy released • produces 36 to 38 ATP per glucose

4. KEY CONCEPTS • Aerobic respiration is an exergonic redox process in which glucose becomes oxidized, oxygen becomes reduced, and energy is captured to make ATP

5. Learning Objective 2 • What are the four stages of aerobic respiration?

6. 4 Stages of Aerobic Respiration • Glycolysis • Formation of acetyl CoA • Citric acid cycle • Electron transport chain and chemiosmosis

7. Glycolysis • 1 molecule of glucose degraded • to 2 molecules pyruvate • 2 ATP molecules (net) produced • by substrate-level phosphorylation • 4 hydrogen atoms removed • to produce 2 NADH

8. Glycolysis

9. Electron transport and chemiosmosis Glycolysis Formation of acetyl coenzyme A Citric acid cycle Glucose Pyruvate 32 ATP 2 ATP 2 ATP Fig. 8-3, p. 175

10. GLYCOLYSIS Energy investment phase and splitting of glucose Two ATPs invested per glucose Glucose 2 ATP 3 steps 2 ADP Fructose-1,6-bisphosphate P P Glyceraldehyde phosphate (G3P) Glyceraldehyde phosphate (G3P) P P Fig. 8-3, p. 175

11. Energy capture phase Four ATPs and two NADH produced per glucose P P (G3P) (G3P) NAD+ NAD+ NADH NADH 5 steps 2 ADP 2 ADP 2 ATP 2 ATP Pyruvate Pyruvate Net yield per glucose: Two ATPs and two NADH Fig. 8-3, p. 175

12. Formation of Acetyl CoA • 1 pyruvate molecule • loses 1 molecule of carbon dioxide • Acetyl group + coenzyme A • produce acetyl CoA • 1 NADH produced per pyruvate

13. Formation of Acetyl CoA

14. Glycolysis Formation of acetyl coenzyme A Citric acid cycle Electron transport and chemiosmosis Glucose Pyruvate 32 ATP 2 ATP 2 ATP Fig. 8-5, p. 178

15. Carbon dioxide CO2 Pyruvate NAD+ Coenzyme A NADH Acetyl coenzyme A Fig. 8-5, p. 178

16. Citric Acid Cycle • 1 acetyl CoA enters cycle • combines with 4-C oxaloacetate • forms 6-C citrate • 2 C enter as acetyl CoA • 2 leave as CO2 • 1 acetyl CoA • transfers H atoms to 3 NAD+, 1 FAD • 1 ATP produced

17. Citric Acid Cycle

18. Formation of acetyl coenzyme A Citric acid cycle Electron transport and chemiosmosis Glycolysis Glucose Pyruvate 2 ATP 2 ATP 32 ATP Fig. 8-6, p. 179

19. Coenzyme A Acetyl coenzyme A Citrate Oxaloacetate NADH NAD+ NAD+ C I T R I C A C I D C Y C L E H2O NADH CO2 FADH2 5-carbon compound FAD NADH GTP GDP CO2 4-carbon compound ADP ATP Fig. 8-6, p. 179

20. Electron Transport Chain • H atoms (or electrons) transfer • from one electron acceptor to another • in mitochondrial inner membrane • Electrons reduce molecular oxygen • forming water

21. Electron Transport Chain

22. Cytosol Outer mitochondrial membrane Intermembrane space Complex IV: Cytochrome c oxidase Complex I: NADH–ubiquinone oxidoreductase Complex III: Ubiquinone– cytochrome c oxidoreductase Complex II: Succinate– ubiquinone reductase Inner mitochondrial membrane Matrix of mitochondrion FADH2 FAD 2 H+ H2O 1/2 O2 NAD+ NADH Fig. 8-8, p. 181

23. Oxidative Phosphorylation • Redox reactions in ETC are coupled to ATP synthesis through chemiosmosis

24. KEY CONCEPTS • Aerobic respiration consists of four stages: glycolysis, formation of acetyl coenzyme A, the citric acid cycle, and the electron transport chain and chemiosmosis

25. Learning Objective 3 • Where in a eukaryotic cell does each stage of aerobic respiration take place?

26. Aerobic Respiration • Glycolysis occurs in the cytosol • All other stages in the mitochondria

27. 1 2 3 4 Glycolysis Formation of acetyl coenzyme A Citric acid cycle Electron transport and chemiosmosis Glucose Mitochondrion Electron transport and chemiosmosis Acetyl coenzyme A Citric acid cycle Pyruvate 2 ATP 2 ATP 32 ATP Fig. 8-2, p. 173

28. Learning Objective 4 • Add up the energy captured (as ATP, NADH, and FADH2) in each stage of aerobic respiration

29. Energy Capture • Glycolysis • 1 glucose: 2 NADH, 2 ATP (net) • Conversion of 2 pyruvates to acetyl CoA • 2 NADH • Citric acid cycle • 2 acetyl CoA: 6 NADH, 2 FADH2, 2 ATP • Total: 4 ATP, 10 NADH, 2 FADH2

30. Energy Transfer • Electron transport chain (ETC) • 10 NADH and 2 FADH2 produce 32 to 34 ATP by chemiosmosis • 1 glucose molecule yields 36 to 38 ATP

31. Energy from Glucose

32. Substrate-level phosphorylation Oxidative phosphorylation Glycolysis Glucose Pyruvate Acetyl coenzyme A Citric acid cycle Total ATP from oxidative phosphorylation Total ATP from substrate-level phosphorylation Fig. 8-11, p. 185

33. Learning Objective 5 • Definechemiosmosis • How is a gradient of protons established across the inner mitochondrial membrane?

34. Chemiosmosis • Energy of electrons in ETC • pumps H+ across inner mitochondrial membrane • into intermembrane space • Protons (H+) accumulate in intermembrane space • lowering pH

35. Proton Gradient

36. Outer mitochondrial membrane Cytosol Inner mitochondrial membrane Intermembrane space — low pH Matrix — higher pH Fig. 8-9, p. 183

37. Learning Objective 6 • How does the proton gradient drive ATP synthesis in chemiosmosis?

38. ATP Synthase • Enzyme ATP synthase • forms channels through inner mitochondrial membrane • Diffusion of protons through channels provides energy to synthesize ATP

39. ETC and Chemiosmosis

40. Cytosol Outer mitochondrial membrane Intermembrane space Complex V: ATP synthase Complex III Complex IV Complex I Inner mitochondrial membrane Complex II Matrix of mitochondrion FADH2 NAD+ 1 2 NADH Pi ADP ATP Fig. 8-10a, p. 184

41. Projections of ATP synthase 250 nm (b) This TEM shows hundreds of projections of ATP synthase complexes along the surface of the inner mitochondrial membrane. Fig. 8-10b, p. 184

42. Learning Objective 7 • How do the products of protein and lipid catabolism enter the same metabolic pathway that oxidizes glucose?

43. Amino Acids • Undergo deamination • Carbon skeletons converted • to intermediates of aerobic respiration

44. Lipids • Glycerol and fatty acids • both oxidized as fuel • Fatty acids • converted to acetyl CoA by β-oxidation

45. Catabolic Pathways

46. PROTEINS CARBOHYDRATES FATS Amino acids Fatty acids Glycerol Glycolysis Glucose G3P Pyruvate CO2 Acetyl coenzyme A Citric acid cycle Electron transport and chemiosmosis End products: H2O CO2 NH3 Fig. 8-12, p. 186

47. PROTEINS CARBOHYDRATES FATS Amino acids Glycerol Fatty acids Glycolysis Glucose G3P Pyruvate CO2 Acetyl coenzyme A Citric acid cycle Electron transport and chemiosmosis NH3 H2O CO2 Stepped Art End products: Fig. 8-12, p. 186

48. KEY CONCEPTS • Nutrients other than glucose, including many carbohydrates, lipids, and amino acids, can be oxidized by aerobic respiration

49. Learning Objective 8 • Compare the mechanism of ATP formation, final electron acceptor, and end products of anaerobic respiration and fermentation

50. Anaerobic Respiration • Electrons transferred • from fuel molecules to ETC • coupled to ATP synthesis (chemiosmosis) • Final electron acceptor • inorganic substance • nitrate or sulfate (not molecular oxygen)