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Chapter 9

Chapter 9. Cellular Respiration. Fig. 9-2. Light energy. ECOSYSTEM. Photosynthesis in chloroplasts. Organic molecules. CO 2 + H 2 O. + O 2. Cellular respiration in mitochondria. ATP. ATP powers most cellular work. Heat energy. I. Catabolic Pathways and Production of ATP.

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Chapter 9

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  1. Chapter 9 Cellular Respiration

  2. Fig. 9-2 Light energy ECOSYSTEM Photosynthesis in chloroplasts Organic molecules CO2 + H2O + O2 Cellular respiration in mitochondria ATP ATP powers most cellular work Heat energy

  3. I. Catabolic Pathways and Production of ATP • Fermentation = partial degradation of sugars that occurs without O2 • Aerobic respiration uses organic molecules and O2 and yields ATP • Anaerobic respiration = similar to aerobic but consumes compounds other than O2

  4. Cellular respiration includes aerobic and anaerobic • C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy (ATP + heat)

  5. II. Redox Reactions: Oxidation and Reduction • Transfer of electrons, releases energy stored in organic molecules, used to synthesize ATP

  6. A. Principle of Redox • Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions • Oxidation = substance loses electrons, oxidized • Reduction = substance gains electrons, reduced (the amount of + charge is reduced) • Electron donor = reducing agent • Electron receptor = oxidizing agent

  7. Fig. 9-UN1 becomes oxidized (loses electron) becomes reduced (gains electron)

  8. Fig. 9-UN2 becomes oxidized becomes reduced

  9. Fig. 9-3 Reactants Products becomes oxidized becomes reduced Carbon dioxide Water Methane (reducing agent) Oxygen (oxidizing agent)

  10. Fig. 9-UN3 becomes oxidized becomes reduced

  11. B. NAD+ and the Electron Transport Chain • Glucose is broken down in a series of steps • Electrons are first transferred to NAD+, a coenzyme • As an electron acceptor, NAD+ functions as an oxidizing agent • Each NADH (the reduced form of NAD+) represents stored energy that is tapped to make ATP • How NAD works

  12. Fig. 9-4 2 e– + 2 H+ 2 e– + H+ H+ NADH Dehydrogenase Reduction of NAD+ NAD+ 2[H] H+ + + Oxidation of NADH Nicotinamide (reduced form) Nicotinamide (oxidized form)

  13. NADH passes the electrons to the electron transport chain • ETC passes electrons in a series of steps instead of one explosive reaction • O2 pulls electrons down the chain in an energy-yielding tumble • The energy yielded regenerates ATP

  14. Fig. 9-5 1/2 O2 H2 + 1/2 O2 + 2 H (from food via NADH) Controlled release of energy for synthesis of ATP 2 H+ + 2 e– ATP Explosive release of heat and light energy ATP Electron transport chain Free energy, G Free energy, G ATP 2 e– 1/2 O2 2 H+ H2O H2O (a) Uncontrolled reaction (b) Cellular respiration

  15. III. Stages of Cellular Respiration: A Preview • Cellular respiration has three stages: • Glycolysis (breaks down glucose into two molecules of pyruvate) • Citric acid cycle (completes the breakdown of glucose) • Oxidative phosphorylation (accounts for most of the ATP synthesis)

  16. Fig. 9-6-1 Electrons carried via NADH Glycolysis Pyruvate Glucose Cytosol ATP Substrate-level phosphorylation

  17. Fig. 9-6-2 Electrons carried via NADH and FADH2 Electrons carried via NADH Citric acid cycle Glycolysis Pyruvate Glucose Mitochondrion Cytosol ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation

  18. Fig. 9-6-3 Electrons carried via NADH and FADH2 Electrons carried via NADH Oxidative phosphorylation: electron transport and chemiosmosis Citric acid cycle Glycolysis Pyruvate Glucose Mitochondrion Cytosol ATP ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation

  19. Oxidative phosphorylation (powered by redox reactions) generates most of the ATP (about 90% of total from cellular resp) • Other 10% of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation

  20. Fig. 9-7 Enzyme Enzyme ADP P Substrate ATP + Product

  21. Concept 9.2: Glycolysis harvests chemical energy by oxidizing glucose to pyruvate • Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate, 2 ATP and 2 NADH (high energy e- carriers) • Glycolysis occurs in the cytoplasm and has two major phases: • Energy investment phase • Energy payoff phase • How glycolysis works

  22. Fig. 9-8 Energy investment phase Glucose 2 ADP + 2 2 ATP used P Energy payoff phase formed 4 ADP + 4 P 4 ATP 2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+ 2 Pyruvate + 2 H2O Net 2 Pyruvate + 2 H2O Glucose 4 ATP formed – 2 ATP used 2 ATP 2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+

  23. Fig. 9-9-1 Glucose ATP 1 Hexokinase ADP Glucose Glucose-6-phosphate ATP 1 Hexokinase ADP Glucose-6-phosphate

  24. Fig. 9-9-2 Glucose ATP 1 Hexokinase ADP Glucose-6-phosphate Glucose-6-phosphate 2 Phosphoglucoisomerase 2 Phosphogluco- isomerase Fructose-6-phosphate Fructose-6-phosphate

  25. Fig. 9-9-3 Glucose ATP 1 1 Hexokinase ADP Fructose-6-phosphate Glucose-6-phosphate 2 2 Phosphoglucoisomerase ATP 3 Phosphofructo- kinase Fructose-6-phosphate ATP ADP 3 3 Phosphofructokinase ADP Fructose- 1, 6-bisphosphate Fructose- 1, 6-bisphosphate

  26. Fig. 9-9-4 Glucose ATP 1 Hexokinase ADP Glucose-6-phosphate 2 Phosphoglucoisomerase Fructose- 1, 6-bisphosphate 4 Fructose-6-phosphate Aldolase ATP 3 Phosphofructokinase ADP 5 Isomerase Fructose- 1, 6-bisphosphate 4 Aldolase 5 Isomerase Glyceraldehyde- 3-phosphate Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate Dihydroxyacetone phosphate

  27. Fig. 9-9-5 2 NAD+ 6 Triose phosphate dehydrogenase 2 P 2 NADH i + 2 H+ 2 2 1, 3-Bisphosphoglycerate Glyceraldehyde- 3-phosphate 2 NAD+ 6 Triose phosphate dehydrogenase P 2 2 NADH i + 2 H+ 2 1, 3-Bisphosphoglycerate

  28. Fig. 9-9-6 2 NAD+ 6 Triose phosphate dehydrogenase 2 P 2 NADH i + 2 H+ 2 1, 3-Bisphosphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP 2 1, 3-Bisphosphoglycerate 2 ADP 2 3-Phosphoglycerate 7 Phosphoglycero- kinase 2 ATP 2 3-Phosphoglycerate

  29. Fig. 9-9-7 2 NAD+ 6 Triose phosphate dehydrogenase 2 P 2 NADH i + 2 H+ 2 1, 3-Bisphosphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP 2 3-Phosphoglycerate 2 3-Phosphoglycerate 8 Phosphoglyceromutase 8 Phosphoglycero- mutase 2 2-Phosphoglycerate 2 2-Phosphoglycerate

  30. Fig. 9-9-8 2 NAD+ 6 Triose phosphate dehydrogenase 2 P 2 NADH i + 2 H+ 2 1, 3-Bisphosphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP 2 2-Phosphoglycerate 2 3-Phosphoglycerate 8 Phosphoglyceromutase 9 Enolase 2 H2O 2 2-Phosphoglycerate 9 Enolase 2 H2O 2 Phosphoenolpyruvate 2 Phosphoenolpyruvate

  31. Fig. 9-9-9 2 NAD+ 6 Triose phosphate dehydrogenase P 2 2 NADH i + 2 H+ 2 1, 3-Bisphosphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP Phosphoenolpyruvate 2 2 ADP 2 3-Phosphoglycerate 8 10 Phosphoglyceromutase Pyruvate kinase 2 ATP 2 2-Phosphoglycerate 9 Enolase 2 H2O 2 Phosphoenolpyruvate 2 ADP 10 Pyruvate kinase 2 ATP Pyruvate 2 2 Pyruvate

  32. IV. Citric acid cycle completes oxidation • With O2, pyruvate enters mitochondrion • Pyruvate must be converted to acetyl CoA, which links the cycle to glycolysis

  33. Fig. 9-10 CYTOSOL MITOCHONDRION NAD+ NADH + H+ 2 1 3 Acetyl CoA Coenzyme A Pyruvate CO2 Transport protein

  34. Citric acid cycle (Krebs cycle) takes place within mito matrix • Cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn (and 2 CO2, cutting up “sugar” even more)

  35. Fig. 9-11 Pyruvate CO2 NAD+ CoA NADH + H+ Acetyl CoA CoA CoA Citric acid cycle 2 CO2 FADH2 3 NAD+ NADH 3 FAD + 3 H+ ADP + P i ATP

  36. Fig. 9-12-8 Acetyl CoA CoA—SH NADH H2O 1 +H+ NAD+ Oxaloacetate 8 2 Malate Citrate Isocitrate NAD+ Citric acid cycle NADH 3 + H+ 7 H2O CO2 Fumarate CoA—SH -Keto- glutarate 4 6 CoA—SH 5 FADH2 CO2 NAD+ FAD Succinate NADH P i + H+ Succinyl CoA GDP GTP ADP ATP

  37. Overview Glycolysis - Citric Acid Cycle

  38. V. Electron Transport Chain • NADH and FADH2 donate e- s to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation • In the cristae of mitochondrion • Carriers alternate reduced and oxidized states as they accept and donate e- • e- s drop in free energy as they go down the chain and are passed to O2, forming H2O

  39. Fig. 9-13 NADH 50 e– 2 NAD+ FADH2 e– 2 FAD Multiprotein complexes  FAD 40 FMN  Fe•S Fe•S Q  Cyt b Fe•S 30 Cyt c1 IV Free energy (G) relative to O2 (kcal/mol) Cyt c Cyt a Cyt a3 20 e– 2 10 (from NADH or FADH2) O2 2 H+ + 1/2 0 H2O

  40. e- s are transferred from NADH or FADH2 to the electron transport chain • Electron transport chain generates no ATP • Function is to break the large free-energy drop from food to O2 into smaller steps that release energy in manageable amounts • Electron Transport Chain and Oxi Phos (3min)

  41. VI. Chemiosmosis: Energy-Coupling • e- transfer in ETC causes proteins to pump H+ from mito matrix to intermembrane space • H+ then moves back across membrane, passing through channels in ATP synthase • ATP synthase uses the exergonic (energy releasing) flow of H+ to drive phosphorylation of ATP (ADP to ATP) • Chemiosmosis = use of energy in a H+ gradient to drive cellular work • H+ gradient is a proton-motive force, emphasizing its capacity to do work

  42. Fig. 9-14 INTERMEMBRANE SPACE H+ Stator Rotor Internal rod Cata- lytic knob ADP + ATP P i MITOCHONDRIAL MATRIX

  43. Fig. 9-16 H+ H+ H+ H+ Protein complex of electron carriers Cyt c V Q   ATP synthase  H2O 2 H+ + 1/2O2 FADH2 FAD NAD+ NADH ADP + ATP P i (carrying electrons from food) H+ Chemiosmosis Electron transport chain 1 2 Oxidative phosphorylation

  44. ETC / Oxi Phos Overview

  45. VII. ATP Production by Cellular Respiration • During cellular respiration, most energy flows in this sequence: glucose  NADH  electron transport chain  proton-motive force  ATP • About 40% of energy in a glucose molecule is transferred to ATP during cellular respiration (about 36 / 38 ATP)

  46. Fig. 9-17 Electron shuttles span membrane MITOCHONDRION CYTOSOL 2 NADH or 2 FADH2 2 NADH 6 NADH 2 FADH2 2 NADH Oxidative phosphorylation: electron transport and chemiosmosis Glycolysis Citric acid cycle 2 Acetyl CoA 2 Pyruvate Glucose + 2 ATP + 2 ATP + about 32 or 34 ATP About 36 or 38 ATP Maximum per glucose:

  47. Cell Respiration Part 2 (9min) • Cellular Respiration Overview - Bozeman (14min)

  48. VIII. Fermentation and anaerobic respiration • W/o O2, glycolysis couples with fermentation or anaerobic respiration to produce ATP • Anaerobic respiration uses an electron transport chain with an electron acceptor other than O2, ex. sulfate • Fermentation uses phosphorylation instead of an electron transport chain to generate ATP

  49. IX. Types of Fermentation • Fermentation = glycolysis plus reactions that regenerate NAD+ (can be reused by glycolysis) • Alcohol fermentation = pyruvate is converted to ethanol in two steps, w/ the first releasing CO2 • Yeast = used in brewing, winemaking, and baking

  50. Fig. 9-18a P 2 ADP + 2 2 ATP i Glucose Glycolysis 2 Pyruvate 2 NAD+ 2 NADH 2 CO2 + 2 H+ 2 Acetaldehyde 2 Ethanol (a) Alcohol fermentation

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