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Cellular Respiration: Energy Production in Living Cells

This chapter explores the process of cellular respiration, the main pathway through which cells obtain energy for their functions. It covers the three stages of cellular respiration: glycolysis, citric acid cycle, and oxidative phosphorylation. The role of redox reactions and ATP production is also discussed.

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Cellular Respiration: Energy Production in Living Cells

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  1. Chapter 9 • Cellular Respiration

  2. Living cells • Require transfusions of energy from outside sources to perform their many tasks

  3. Figure 9.1 • The giant panda obtains energy for its cells by eating plants

  4. Light energy ECOSYSTEM Photosynthesisin chloroplasts Organicmolecules CO2 + H2O + O2 Cellular respirationin mitochondria ATP powers most cellular work Heatenergy Figure 9.2 • Energy flows into ecosystem as sunlight, leaves as heat

  5. Catabolic pathways yield E by oxidizing organic fuels

  6. Catabolic Pathways and Production of ATP • Breakdown of organic molecules is exergonic

  7. Cellular respiration • Most prevalent and efficient catabolic pathway • Consumes O2 and organic molecules e.g. glucose • Yields ATP

  8. To keep working cells regenerate ATP

  9. Redox Reactions: Oxidation and Reduction • Catabolic pathways yield energy • Due to the transfer of electrons (e-)

  10. Oxidation • Lose e- (oxidized) • Reduction • Gain e-, (reduced)

  11. becomes oxidized(loses electron) Na + Cl Na+ + Cl– becomes reduced(gains electron) • Example of redox reaction

  12. Oxidation of Organic Fuel Molecules During Cellular Respiration • Glucose is oxidized and oxygen is reduced

  13. Stepwise Energy Harvest • Glucose oxidized in a series of steps

  14. 2 e– + 2 H+ 2 e– + H+ NAD+ NADH H Dehydrogenase O O H H Reduction of NAD+ + + 2[H] C NH2 NH2 C (from food) Oxidation of NADH N N+ Nicotinamide(reduced form) Nicotinamide(oxidized form) CH2 O O O O– P O H H OH O O– HO P NH2 HO CH2 O N N H N H N O H H HO OH Figure 9.4 • Electrons f/ organic compounds • Usually first transferred to NAD+, a coenzyme

  15. NADH (reduced form of NAD+) • Passes electrons to the e- transport chain

  16. H2 + 1/2 O2 Explosiverelease ofheat and lightenergy (a) Uncontrolled reaction Free energy, G H2O Figure 9.5 A • Non stepwise e- transfer • Lg. release of E

  17. e- transport chain • Passes e- in a series of steps instead of explosive reaction • Uses E from the e- transfer to form ATP

  18. 2 H + 1/2 O2 (from food via NADH) Controlled release of energy for synthesis ofATP 2 H+ + 2 e– ATP ATP Free energy, G Electron transport chain ATP 2 e– 1/2 O2 2 H+ H2O Figure 9.5 B (b) Cellular respiration

  19. The 3 Stages of Cellular Respiration • Glycolysis • Citric acid cycle (Kreb’s cycle) • Oxidative phosphorylation

  20. Glycolysis • Breaks down glucose into two molecules of pyruvate • Citric acid (Kreb’s)cycle • Completes breakdown of glucose

  21. Oxidative phosphorylation • Driven by e- transport chain • Generates ATP

  22. Glycolsis Glucose Pyruvate Mitochondrion ATP Substrate-level phosphorylation Overview of cellular respiration

  23. Citric acid cycle Glycolsis Glucose Pyruvate Mitochondrion ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation

  24. Electrons carried via NADH Electrons carried via NADH and FADH2 Oxidativephosphorylation:electron transportandchemiosmosis Glycolsis Citric acid cycle Glucose Pyruvate Mitochondrion ATP ATP ATP Substrate-level phosphorylation Oxidative phosphorylation Substrate-level phosphorylation

  25. Electrons carried via NADH and FADH2 Electrons carried via NADH Oxidativephosphorylation:electron transport andchemiosmosis Citric acid cycle Glycolsis Pyruvate Glucose Cytosol Mitochondrion ATP ATP ATP Substrate-level phosphorylation Oxidative phosphorylation Substrate-level phosphorylation Figure 9.6 • Overview of cellular respiration

  26. Enzyme Enzyme ADP P Substrate + ATP Product Figure 9.7 • Glycolysis and citric acid cycle generate ATP by substrate-level phosphorylation

  27. Glycolysis harvests E by oxidizing glucose to pyruvate • Glycolysis • Means “splitting sugar” • Glucose  pyruvate • Occurs in cytoplasm

  28. Glycolysis Oxidativephosphorylation Citricacidcycle ATP ATP ATP Energy investment phase Glucose P 2 ATP + 2 used 2 ATP Energy payoff phase formed P 4 ATP 4 ADP + 4 2 NAD+ + 4 e- + 4 H + + 2 H+ 2 NADH 2 Pyruvate + 2 H2O Glucose 2 Pyruvate + 2 H2O 4 ATP formed – 2 ATP used 2 ATP + 2 H+ 2 NADH 2 NAD+ + 4 e– + 4 H + Figure 9.8 • 2 major phases • E investment phase • E payoff phase

  29. E investment phase

  30. CH2OH Citric acid cycle H H Oxidative phosphorylation H Glycolysis H HO HO OH H OH Glucose 1 2 3 5 4 ATP Hexokinase ADP CH2OH P O H H H H OH HO H OH Glucose-6-phosphate Phosphoglucoisomerase CH2O P O CH2OH H HO HO H H HO Fructose-6-phosphate ATP Phosphofructokinase ADP CH2 O O CH2 P P O HO H OH H HO Fructose- 1, 6-bisphosphate Aldolase H O CH2 P Isomerase C O O C CHOH CH2OH O CH2 P Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate Figure 9.9 A

  31. E payoff phase

  32. 2 NAD+ Triose phosphate dehydrogenase P i 2 2 NADH + 2 H+ 10 7 9 8 6 2 O C O P CHOH P CH2 O 1, 3-Bisphosphoglycerate 2 ADP Phosphoglycerokinase 2 ATP O– 2 C CHOH O P CH2 3-Phosphoglycerate Phosphoglyceromutase O– 2 C O P C H O CH2OH 2-Phosphoglycerate Enolase 2 H2O O– 2 C O P C O CH2 Phosphoenolpyruvate 2 ADP Pyruvate kinase 2 ATP O– 2 C O C O CH3 Figure 9.8 B Pyruvate

  33. Citric acid (Kreb’s) cycle completes the E-yielding oxidation of organic molecules • Takes place in matrix of mitochondrion

  34. CYTOSOL MITOCHONDRION + H+ NAD+ NADH O– CoA S 2 C O C O C O CH3 1 3 CH3 Acetyle CoA Pyruvate CO2 Coenzyme A Transport protein Figure 9.10 • Pyruvate first converted to acetyl CoA, links cycle to glycolysis

  35. Pyruvate(from glycolysis,2 molecules per glucose) Oxidativephosphorylation Glycolysis Citricacidcycle ATP ATP ATP CO2 CoA NADH + 3 H+ Acetyle CoA CoA CoA Citricacidcycle 2 CO2 FADH2 3 NAD+ 3 NADH FAD + 3 H+ ADP + Pi ATP Figure 9.11 • Overview of citric acid cycle

  36. Closer look at citric acid cycle

  37. Citric acid cycle Oxidative phosphorylation Glycolysis S CoA C O CH3 Acetyl CoA CoA SH H2O O C COO– NADH 1 COO– CH2 + H+ COO– CH2 COO– NAD+ Oxaloacetate 8 C COO– HO CH2 2 CH2 HC COO– COO– COO– HO CH HO CH Malate Citrate COO– CH2 Isocitrate COO– CO2 Citric acid cycle 3 H2O 7 NAD+ COO– NADH COO– CH + H+ Fumarate CH2 CoA SH HC a-Ketoglutarate CH2 COO– C O 4 6 SH CoA COO– COO– COO– CH2 5 CH2 FADH2 CO2 CH2 CH2 NAD+ FAD C O COO– Succinate NADH CoA S P i + H+ Succinyl CoA GDP GTP ADP ATP Figure 9.12 Figure 9.12

  38. Oxidative phosphorylation • Chemiosmosis couples e- transport to ATP synthesis • NADH and FADH2 • Donate e- to e- transport chain, which powers ATP synthesis via oxidative phosphorylation

  39. Electron Transport Chain • e- from NADH and FADH2 lose E in steps

  40. NADH 50 FADH2 Multiproteincomplexes I 40 FAD FMN II Fe•S Fe•S O III Cyt b 30 Fe•S Cyt c1 IV Cyt c Free energy (G) relative to O2 (kcl/mol) Cyt a Cyt a3 20 10 0 O2 2 H + + 12 Figure 9.13 H2O • At end of the chain e- passed to O2, forming water

  41. A rotor within the membrane spins clockwise whenH+ flows past it down the H+ gradient. INTERMEMBRANE SPACE H+ H+ H+ H+ H+ H+ H+ A stator anchoredin the membraneholds the knobstationary. A rod (for “stalk”)extending into the knob alsospins, activatingcatalytic sites inthe knob. H+ Three catalytic sites in the stationary knobjoin inorganic Phosphate to ADPto make ATP. ADP + ATP P i MITOCHONDRIAL MATRIX Figure 9.14 Chemiosmosis: The Energy-Coupling Mechanism • ATP synthase • Enzyme that actually makes ATP

  42. e- transfer pumps H+ f/ mitochondrial matrix to intermembrane space

  43. Resulting H+ gradient • Stores E • Drives chemiosmosis • Referred to as a proton-motive force

  44. Chemiosmosis • E-coupling mechanism, drives cellular work

  45. Inner Mitochondrial membrane Oxidative phosphorylation. electron transport and chemiosmosis Glycolysis ATP ATP ATP H+ H+ H+ H+ Cyt c Protein complex of electron carners Intermembrane space Q IV I III ATP synthase Inner mitochondrial membrane II H2O FADH2 2 H+ + 1/2 O2 FAD+ NADH+ NAD+ ATP ADP + P i (Carrying electrons from, food) H+ Mitochondrial matrix Chemiosmosis ATP synthesis powered by the flow Of H+ back across the membrane Electron transport chain Electron transport and pumping of protons (H+), which create an H+ gradient across the membrane Figure 9.15 Oxidative phosphorylation • Chemiosmosis and the e- transport chain

  46. An Accounting of ATP Production by Cellular Respiration • During respiration, most E flows: • Glucose  NADH  electron transport chain  proton-motive force  ATP

  47. Electron shuttles span membrane MITOCHONDRION CYTOSOL 2 NADH or 2 FADH2 2 FADH2 2 NADH 2 NADH 6 NADH Glycolysis Oxidative phosphorylation: electron transport and chemiosmosis Citric acid cycle 2 Acetyl CoA 2 Pyruvate Glucose + 2 ATP + 2 ATP + about 32 or 34 ATP by oxidative phosphorylation, depending on which shuttle transports electrons from NADH in cytosol by substrate-level phosphorylation by substrate-level phosphorylation About 36 or 38 ATP Maximum per glucose: Figure 9.16 • 3 main processes in metabolism

  48. ~ 40% of E in a glucose molecule • Transferred to ATP during cellular respiration, making ~ 38 ATP

  49. Fermentation; produces ATP w/o O2 • Cellular respiration • Relies on O2 to produce ATP • In the absence of O2 fermentation

  50. Glycolysis • Produces ATP w/ or w/o oxygen, aerobic or anaerobic conditions • Couples w/ fermentation to produce ATP

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