1. Slide 1 of 37 Copyright Pearson Prentice Hall 9-2 The Krebs Cycle and Electron Transport

2. Slide 2 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall 9-2 The Krebs Cycle and Electron Transport Oxygen is required for the final steps of cellular respiration. Because the pathways of cellular respiration require oxygen, they are aerobic. **(Remember, glycolysis and fermentation didn’t require oxygen)

3. Slide 3 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall If oxygen is present If no oxygen

4. Slide 4 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall

5. Slide 5 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall Overview of Cellular Respiration Cytoplasm Pyruvic acid Mitochondrion Electrons carried in NADH Electrons carried in NADH and FADH 2 Glucose Glycolysis

6. Slide 6 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall The Krebs Cycle In the presence of oxygen, pyruvic acid produced in glycolysis passes to the second stage of cellular respiration, the Krebs cycle.

7. Slide 7 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall The Krebs Cycle What happens during the Krebs cycle?

8. Slide 8 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall The Krebs Cycle During the Krebs cycle, pyruvic acid is broken down into carbon dioxide in a series of energy-extracting reactions.

9. Slide 9 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall The Krebs Cycle The Krebs cycle begins when pyruvic acid produced by glycolysis enters the mitochondrion.

10. Slide 10 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall The Krebs Cycle One carbon molecule is removed, forming CO 2, and electrons are removed, added to NAD+,changing NAD + to NADH.

11. Slide 11 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall The Krebs Cycle Coenzyme A joins the 2-carbon molecule, forming acetyl-CoA.

12. Slide 12 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall The Krebs Cycle Citric acid Acetyl-CoA then adds the 2-carbon acetyl group to a 4- carbon compound, forming citric acid. Now watch the cycle.

13. Slide 13 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall The Krebs Cycle For each pyruvic acid, two more molecules of CO 2 are released and electrons join NAD + and FAD, forming NADH and FADH 2.

14. Slide 14 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall The Krebs Cycle In addition, one molecule of ATP is generated.

15. Slide 15 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall The Krebs Cycle The energy tally from 1 molecule of pyruvic acid is 4 NADH 1 FADH 2 1 ATP So what are the totals with 2 pyruvic acids? 8 NADH 2 FADH 2 2 ATP

16. Slide 16 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall Some things to note: How much CO 2 was produced? 6 total ( 3 CO 2 per pyruvic acid ) How much oxygen was used? None so far How much ATP has been made? 2 ATP in Kreb’s ( 4 ATP overall—two from glycolysis)

17. Slide 17 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall The Krebs Cycle What does the cell do with all those high-energy electrons in carriers like NADH and FADH 2 ? In the presence of oxygen, those high-energy electrons can be used to generate HUGE amounts of ATP.

18. Slide 18 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall Electron Transport How are high-energy electrons used by the electron transport chain?

19. Slide 19 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall Electron Transport The electron transport chain uses the high- energy electrons from the Krebs cycle to convert ADP into ATP.

20. Slide 20 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall Electron Transport 1. High-energy e - AND H + from NADH and FADH 2 are broken off & passed along the electron transport chain from one carrier protein to the next.

21. Slide 21 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall Electron Transport 2.H+ are pumped to other side 3.At the end of the chain, an enzyme combines these electrons with hydrogen ions and oxygen to form water.

22. Slide 22 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall Electron Transport As the final electron acceptor of the electron transport chain, oxygen gets rid of the low-energy electrons and hydrogen ions: form H 2 O

23. Slide 23 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall Electron Transport When 2 high-energy electrons move down the electron transport chain, their energy is used to move hydrogen ions (H + ) across the membrane.

24. Slide 24 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall Electron Transport During electron transport, H + ions build up in the intermembrane space, so it is positively charged.

25. Slide 25 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall Electron Transport The other side of the membrane, from which those H + ions are taken, is now negatively charged.

26. Slide 26 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall Electron Transport ATP synthase The inner membranes of the mitochondria contain protein spheres called ATP synthases.

27. Slide 27 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall Electron Transport 4. As H + ions escape through channels into these proteins, the ATP synthase spins. ATP synthase Channel

28. Slide 28 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall Electron Transport 4. As it rotates, the enzyme grabs a low-energy ADP, attaching a phosphate, forming high-energy ATP. ADP ATP synthase Channel P

29. Slide 29 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall Electron Transport On average, each pair of high-energy electrons that moves down the electron transport chain provides enough energy to produce three molecules of ATP from each NADH two molecules of ATP from each FADH 2.

30. Slide 30 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall The Totals Glycolysis produces just 2 ATP molecules per molecule of glucose. The complete breakdown of glucose through cellular respiration, including glycolysis, results in the NET production of 36 molecules of ATP.

31. Slide 31 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall The Totals

32. Slide 32 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall Comparing Photosynthesis and Cellular Respiration The energy flows in photosynthesis and cellular respiration take place in opposite directions.

33. 9-2 The Krebs Cycle and Electron Transport Slide 33 of 37 Copyright Pearson Prentice Hall Comparing Photosynthesis and Cellular Respiration On a global level, photosynthesis and cellular respiration are also opposites. Photosynthesis removes carbon dioxide from the atmosphere and cellular respiration puts it back. Photosynthesis releases oxygen into the atmosphere and cellular respiration uses that oxygen to release energy from food.

34. - or - Continue to: Click to Launch: Slide 34 of 37 Copyright Pearson Prentice Hall 9-2

35. Slide 35 of 37 Copyright Pearson Prentice Hall 9-2 The Krebs cycle breaks pyruvic acid down into a.oxygen. b.NADH. c.carbon dioxide. d.alcohol.

36. Slide 36 of 37 Copyright Pearson Prentice Hall 9-2 What role does the Krebs cycle play in the cell? a.It breaks down glucose and releases its stored energy. b.It releases energy from molecules formed during glycolysis. c.It combines carbon dioxide and water into high-energy molecules. d.It breaks down ATP and NADH, releasing stored energy.

37. Slide 37 of 37 Copyright Pearson Prentice Hall 9-2 In eukaryotes, the electron transport chain is located in the a.cell membrane. b.inner mitochondrial membrane. c.cytoplasm. d.outer mitochondrial membrane.

38. Slide 38 of 37 Copyright Pearson Prentice Hall 9-2 To generate energy over long periods, the body must use a.stored ATP. b.lactic acid fermentation. c.cellular respiration. d.glycolysis.

39. Slide 39 of 37 Copyright Pearson Prentice Hall 9-2 Which statement correctly describes photosynthesis and cellular respiration? a.Photosynthesis releases energy, while cellular respiration stores energy. b.Photosynthesis and cellular respiration use the same raw materials. c.Cellular respiration releases energy, while photosynthesis stores energy. d.Cellular respiration and photosynthesis produce the same products.

40. Slide 40 of 37 9-2 The Krebs Cycle and Electron Transport Copyright Pearson Prentice Hall END OF SECTION