1. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings PowerPoint Lectures for Biology, Seventh Edition Neil Campbell and Jane Reece Lectures by Chris Romero Chapter 9 Cellular Respiration: Harvesting Chemical Energy

2. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Energy – Flows into an ecosystem as sunlight and leaves as heat Light energy ECOSYSTEM CO 2 + H 2 O Photosynthesis in chloroplasts Cellular respiration in mitochondria Organic molecules + O 2 ATP powers most cellular work Heat energy Figure 9.2

3. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels The breakdown of organic molecules is exergonic

4. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Cellular respiration – Is the most prevalent and efficient catabolic pathway – Consumes oxygen and organic molecules such as glucose – Yields ATP

5. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Redox Reactions: Oxidation and Reduction Catabolic pathways yield energy – Due to the transfer of electrons Redox reactions – Transfer electrons from one reactant to another by oxidation and reduction

6. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings In oxidation – A substance loses electrons, or is oxidized In reduction – A substance gains electrons, or is reduced

7. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Stepwise Energy Harvest via NAD + and the Electron Transport Chain Cellular respiration – Oxidizes glucose in a series of steps

8. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Electrons from organic compounds – Are usually first transferred to NAD +, a coenzyme NAD + H O O OO–O– O O O–O– O O O P P CH 2 HO OH H H HOOH HO H H N+N+ C NH 2 H N H N N Nicotinamide (oxidized form) NH 2 + 2[H] (from food) Dehydrogenase Reduction of NAD + Oxidation of NADH 2 e – + 2 H + 2 e – + H + NADH O H H N C + Nicotinamide (reduced form) N Figure 9.4

9. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings NADH, the reduced form of NAD + – Passes the electrons to the electron transport chain

10. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The electron transport chain – Passes electrons in a series of steps instead of in one explosive reaction – Uses the energy from the electron transfer to form ATP

11. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Stages of Cellular Respiration: A Preview Respiration is a cumulative function of four metabolic stages – Glycolysis – Grooming – The citric acid cycle – Oxidative phosphorylation

12. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis – Breaks down glucose into two molecules of pyruvate The citric acid cycle – Completes the breakdown of glucose

13. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Oxidative phosphorylation – Is driven by the electron transport chain – Generates ATP

14. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An overview of cellular respiration Figure 9.6 Electrons carried via NADH Glycolsis Glucose Pyruvate ATP Substrate-level phosphorylation Electrons carried via NADH and FADH 2 Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis ATP Substrate-level phosphorylation Oxidative phosphorylation Mitochondrion Cytosol

15. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Both glycolysis and the citric acid cycle – Can generate ATP by substrate-level phosphorylation Figure 9.7 Enzyme ATP ADP Product Substrate P +

16. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 9.2: Glycolysis harvests energy by oxidizing glucose to pyruvate Glycolysis – Means “splitting of sugar” – Breaks down glucose into pyruvate – Occurs in the cytoplasm of the cell

17. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis consists of two major phases – Energy investment phase – Energy payoff phase Glycolysis Citric acid cycle Oxidative phosphorylation ATP 2 ATP 4 ATP used formed Glucose 2 ATP + 2 P 4 ADP + 4 P 2 NAD + + 4 e - + 4 H + 2 NADH + 2 H + 2 Pyruvate + 2 H 2 O Energy investment phase Energy payoff phase Glucose 2 Pyruvate + 2 H 2 O 4 ATP formed – 2 ATP used 2 ATP 2 NAD + + 4 e – + 4 H + 2 NADH + 2 H + Figure 9.8

18. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate H H H H H OH HO CH 2 OH H H H H O H OH HO OH P CH 2 O P H O H HO H CH 2 OH P O CH 2 O O P HO H H OH O P CH 2 C O CH 2 OH H C CHOH CH 2 O O P ATP ADP Hexokinase Glucose Glucose-6-phosphate Fructose-6-phosphate ATP ADP Phosphoglucoisomerase Phosphofructokinase Fructose- 1, 6-bisphosphate Aldolase Isomerase Glycolysis 1 2 3 4 5 CH 2 OH Oxidative phosphorylation Citric acid cycle Figure 9.9 A

19. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 NAD + NADH 2 + 2 H + Triose phosphate dehydrogenase 2 P i 2 P C CHOH O P O CH 2 O 2 O–O– 1, 3-Bisphosphoglycerate 2 ADP 2 ATP Phosphoglycerokinase CH 2 OP 2 C CHOH 3-Phosphoglycerate Phosphoglyceromutase O–O– C C CH 2 OH H O P 2-Phosphoglycerate 2 H 2 O 2 O–O– Enolase C C O P O CH 2 Phosphoenolpyruvate 2 ADP 2 ATP Pyruvate kinase O–O– C C O O CH 3 2 6 8 7 9 10 Pyruvate O Figure 9.8 B

20. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Before the citric acid cycle can begin – Pyruvate must first be converted to acetyl CoA, which links the cycle to glycolysis CYTOSOLMITOCHONDRION NADH + H + NAD + 2 31 CO 2 Coenzyme A Pyruvate Acetyle CoA S CoA C CH 3 O Transport protein O–O– O O C C CH 3 Figure 9.10

21. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An overview of the citric acid cycle ATP 2 CO 2 3 NAD + 3 NADH + 3 H + ADP + P i FAD FADH 2 Citric acid cycle CoA Acetyle CoA NADH + 3 H + CoA CO 2 Pyruvate (from glycolysis, 2 molecules per glucose) ATP Glycolysis Citric acid cycle Oxidative phosphorylatio n Figure 9.11

22. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Figure 9.12 Acetyl CoA NADH Oxaloacetate Citrate Malate Fumarate Succinate Succinyl CoA  -Ketoglutarate Isocitrate Citric acid cycle SCoA SH NADH FADH 2 FAD GTP GDP NAD + ADP P i NAD + CO 2 CoA SH CoA SH CoA S H2OH2O + H + H2OH2O C CH 3 O OCCOO – CH 2 COO – CH 2 HO C COO – CH 2 COO – CH 2 HCCOO – HOCH COO – CH CH 2 COO – HO COO – CH HC COO – CH 2 COO – CH 2 CO COO – CH 2 CO COO – 1 2 3 4 5 6 7 8 Glycolysis Oxidative phosphorylation NAD + + H + ATP Citric acid cycle Figure 9.12

23. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 9.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis NADH and FADH 2 – Donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation

24. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Pathway of Electron Transport In the electron transport chain – Electrons from NADH and FADH 2 lose energy in several steps

25. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings At the end of the chain – Electrons are passed to oxygen, forming water H2OH2O O2O2 NADH FADH2 FMN FeS O FAD Cyt b Cyt c 1 Cyt c Cyt a Cyt a 3 2 H + + 1  2 I II III IV Multiprotein complexes 0 10 20 30 40 50 Free energy (G) relative to O 2 (kcl/mol) Figure 9.13

26. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis: The Energy-Coupling Mechanism ATP synthase – Is the enzyme that actually makes ATP INTERMEMBRANE SPACE H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ P i + ADP ATP A rotor within the membrane spins clockwise when H + flows past it down the H + gradient. A stator anchored in the membrane holds the knob stationary. A rod (for “stalk”) extending into the knob also spins, activating catalytic sites in the knob. Three catalytic sites in the stationary knob join inorganic Phosphate to ADP to make ATP. MITOCHONDRIAL MATRIX Figure 9.14

27. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings At certain steps along the electron transport chain – Electron transfer causes protein complexes to pump H + from the mitochondrial matrix to the intermembrane space

28. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The resulting H + gradient – Stores energy – Drives chemiosmosis in ATP synthase – Is referred to as a proton-motive force

29. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis – Is an energy-coupling mechanism that uses energy in the form of a H + gradient across a membrane to drive cellular work

30. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Chemiosmosis and the electron transport chain Oxidative phosphorylation. electron transport and chemiosmosis Glycolysis ATP Inner Mitochondrial membrane H+H+ H+H+ H+H+ H+H+ H+H+ ATP P i Protein complex of electron carners Cyt c I II III IV (Carrying electrons from, food) NADH + FADH 2 NAD + FAD + 2 H + + 1 / 2 O 2 H2OH2O ADP + Electron transport chain Electron transport and pumping of protons (H + ), which create an H + gradient across the membrane Chemiosmosis ATP synthesis powered by the flow Of H + back across the membrane ATP synthase Q Oxidative phosphorylation Intermembrane space Inner mitochondrial membrane Mitochondrial matrix Figure 9.15

31. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings An Accounting of ATP Production by Cellular Respiration During respiration, most energy flows in this sequence – Glucose to NADH to electron transport chain to proton-motive force to ATP

32. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings There are three main processes in this metabolic enterprise Electron shuttles span membrane CYTOSOL 2 NADH 2 FADH 2 2 NADH 6 NADH 2 FADH 2 2 NADH Glycolysis Glucose 2 Pyruvate 2 Acetyl CoA Citric acid cycle Oxidative phosphorylation: electron transport and chemiosmosis MITOCHONDRION by substrate-level phosphorylation by substrate-level phosphorylation by oxidative phosphorylation, depending on which shuttle transports electrons from NADH in cytosol Maximum per glucose: About 36 or 38 ATP + 2 ATP + about 32 or 34 ATP or Figure 9.16

33. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings About 40% of the energy in a glucose molecule – Is transferred to ATP during cellular respiration, making approximately 38 ATP

34. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Concept 9.5: Fermentation enables some cells to produce ATP without the use of oxygen Cellular respiration – Relies on oxygen to produce ATP In the absence of oxygen – Cells can still produce ATP through fermentation

35. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Glycolysis – Can produce ATP with or without oxygen, in aerobic or anaerobic conditions – Couples with fermentation to produce ATP

36. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Types of Fermentation Fermentation consists of – Glycolysis plus reactions that regenerate NAD +, which can be reused by glyocolysis

37. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings 2 ADP + 2 P1P1 2 ATP Glycolysis Glucose 2 NAD + 2 NADH 2 Pyruvate 2 Acetaldehyde 2 Ethanol (a) Alcohol fermentation 2 ADP + 2 P1P1 2 ATP Glycolysis Glucose 2 NAD + 2 NADH 2 Lactate (b) Lactic acid fermentation H H OH CH 3 C O – O C CO CH 3 H CO O–O– CO CO O CO C OHH CH 3 CO 2 2 Figure 9.17

38. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings Pyruvate is a key juncture in catabolism Glucose CYTOSOL Pyruvate No O 2 present Fermentation O 2 present Cellular respiration Ethanol or lactate Acetyl CoA MITOCHONDRION Citric acid cycle Figure 9.18

39. Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings The Evolutionary Significance of Glycolysis Glycolysis – Occurs in nearly all organisms – Probably evolved in ancient prokaryotes before there was oxygen in the atmosphere