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PowerLecture: Chapter 8

PowerLecture: Chapter 8. How Cells Release Stored Energy. Impacts, Issues: When Mitochondria Spin Their Wheels. More than 100 mitochondrial disorders are known Friedreich’s ataxia , caused by a mutant gene, results in loss of cordination, weak muscles, and visual problems

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PowerLecture: Chapter 8

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  1. PowerLecture:Chapter 8 How Cells Release Stored Energy

  2. Impacts, Issues: When Mitochondria Spin Their Wheels • More than 100 mitochondrial disorders are known • Friedreich’s ataxia, caused by a mutant gene, results in loss of cordination, weak muscles, and visual problems • Animal, plants, fungus, and most protists depend on structurally sound mitochondria • Defective mitochondria can result in life threatening disorders

  3. When Mitochondria Spin Their Wheels Fig. 8-1, p.122

  4. “Killer” Bees • Descendents of African honeybees that were imported to Brazil in the 1950s • More aggressive, wider-ranging than other honeybees • Africanized bee’s muscle cells have large mitochondria

  5. ATP Is Universal Energy Source • Photosynthesizers get energy from the sun • Animals get energy second- or third-hand from plants or other organisms • Regardless, the energy is converted to the chemical bond energy of ATP

  6. Making ATP • Plants make ATP during photosynthesis • Cells of all organisms make ATP by breaking down carbohydrates, fats, and protein

  7. Main Types of Energy-Releasing Pathways Anaerobic pathways • Evolved first • Don’t require oxygen • Start with glycolysis in cytoplasm • Completed in cytoplasm Aerobic pathways • Evolved later • Require oxygen • Start with glycolysis in cytoplasm • Completed in mitochondria

  8. Main Types of Energy-Releasing Pathways start (glycolysis) in cytoplasm start (glycolysis) in cytoplasm completed in cytoplasm completed in mitochondrion Anaerobic Energy-Releasing Pathways Aerobic Respiration Fig. 8-2, p.124

  9. Summary Equation for Aerobic Respiration C6H1206 + 6O2 6CO2 + 6H20 glucose oxygen carbon water dioxide

  10. CYTOPLASM glucose ATP 4 2 ATP Glycolysis e- + H+ (2 ATP net) 2 pyruvate 2 NADH Overview of Aerobic Respiration e- + H+ 2 CO2 2 NADH e- + H+ 4 CO2 8 NADH KrebsCycle e- + H+ 2 ATP 2 FADH2 e- Electron Transfer Phosphorylation 32 ATP H+ water e- +oxygen Typical Energy Yield: 36 ATP Fig. 8-3, p. 135

  11. The Role of Coenzymes • NAD+ and FAD accept electrons and hydrogen • Become NADH and FADH2 • Deliver electrons and hydrogen to the electron transfer chain

  12. Glucose • A simple sugar (C6H12O6) • Atoms held together by covalent bonds In-text figurePage 126

  13. Glycolysis Occurs in Two Stages • Energy-requiring steps • ATP energy activates glucose and its six-carbon derivatives • Energy-releasing steps • The products of the first part are split into three-carbon pyruvate molecules • ATP and NADH form

  14. glucose Glycolysis GYCOLYSIS pyruvate to second stage of aerobic respiration or to a different energy-releasing pathway GLUCOSE Fig. 8-4a, p.126

  15. Glycolysis ENERGY-REQUIRING STEPS OF GLYCOLYSIS glucose ATP 2 ATP invested ADP P glucose–6–phosphate P fructose–6–phosphate ATP ADP P P fructose–1,6–bisphosphate DHAP Fig. 8-4b, p.127

  16. Glycolysis ENERGY-RELEASING STEPS OF GLYCOLYSIS P P PGAL PGAL NAD+ NAD+ NADH NADH Pi Pi P P P P 1,3–bisphosphoglycerate 1,3–bisphosphoglycerate substrate-level phsphorylation ADP ADP ATP ATP 2 ATP invested P P 3–phosphoglycerate 3–phosphoglycerate Fig. 8-4c, p.127

  17. Glycolysis P P 2–phosphoglycerate 2–phosphoglycerate H2O H2O P P PEP PEP substrate-level phsphorylation ADP ADP ATP ATP 2 ATP produced pyruvate pyruvate Fig. 8-4d, p.127

  18. Glycolysis: Net Energy Yield Energy requiring steps: 2 ATP invested Energy releasing steps: 2 NADH formed 4 ATP formed Net yield is 2 ATP and 2 NADH

  19. Second Stage Reactions • Preparatory reactions • Pyruvate is oxidized into two-carbon acetyl units and carbon dioxide • NAD+ is reduced • Krebs cycle • The acetyl units are oxidized to carbon dioxide • NAD+and FAD are reduced

  20. Second Stage Reactions inner mitochondrial membrane outer mitochondrial membrane inner compartment outer compartment Fig. 8-6a, p.128

  21. O O Preparatory Reactions pyruvate coenzyme A (CoA) NAD+ carbon dioxide NADH CoA acetyl-CoA

  22. The Krebs Cycle Overall Reactants • Acetyl-CoA • 3 NAD+ • FAD • ADP and Pi Overall Products • Coenzyme A • 2 CO2 • 3 NADH • FADH2 • ATP

  23. Acetyl-CoA Formation pyruvate Preparatory Reactions coenzyme A NAD+ (CO2) NADH CoA acetyl-CoA Krebs Cycle CoA oxaloacetate citrate NAD+ NADH NADH NAD+ NAD+ FADH2 FAD NADH ADP + phosphate group ATP Fig. 8-7a, p.129

  24. Results of the Second Stage • All of the carbon molecules in pyruvate end up in carbon dioxide • Coenzymes are reduced (they pick up electrons and hydrogen) • One molecule of ATP forms • Four-carbon oxaloacetate regenerates

  25. Two pyruvates cross the inner mitochondrial membrane. outer mitochondrial compartment inner mitochondrial compartment NADH 2 NADH 6 Krebs Cycle Eight NADH, two FADH 2, and two ATP are the payoff from the complete break-down of two pyruvates in the second-stage reactions. FADH2 2 ATP 2 The six carbon atoms from two pyruvates diffuse out of the mitochondrion, then out of the cell, in six CO 6 CO2 Fig. 8-6b, p.128

  26. Coenzyme Reductions during First Two Stages • Glycolysis 2 NADH • Preparatory reactions 2 NADH • Krebs cycle 2 FADH2 + 6 NADH • Total 2 FADH2 + 10 NADH

  27. Phosphorylation glucose ATP 2 PGAL ATP 2 NADH 2 pyruvate glycolysis 2 FADH2 2 CO2 e– 2 acetyl-CoA 2 NADH H+ H+ 6 NADH KREBS CYCLE 2 ATP Krebs Cycle ATP H+ 2 FADH2 ATP H+ 4 CO2 36 ATP H+ H+ ADP + Pi electron transfer phosphorylation H+ H+ H+ Fig. 8-9, p.131

  28. Electron Transfer Phosphorylation • Occurs in the mitochondria • Coenzymes deliver electrons to electron transfer chains

  29. Creating an H+ Gradient Electron transfer sets up H+ ion gradients OUTER COMPARTMENT NADH INNER COMPARTMENT

  30. Making ATP: Chemiosmotic Model Flow of H+ down gradients powers ATP formation ATP INNER COMPARTMENT ADP+Pi

  31. Importance of Oxygen • Electron transport phosphorylation requires the presence of oxygen • Oxygen withdraws spent electrons from the electron transfer chain, then combines with H+ to form water

  32. Anaerobic Pathways • Do not use oxygen • Produce less ATP than aerobic pathways • Two types • Fermentation pathways • Anaerobic electron transport

  33. Fermentation Pathways • Begin with glycolysis • Do not break glucose down completely to carbon dioxide and water • Yield only the 2 ATP from glycolysis • Steps that follow glycolysis serve only to regenerate NAD+

  34. glycolysis Alcoholic Fermentation C6H12O6 ATP 2 energy input 2 ADP 2 NAD+ NADH 2 4 ATP 2 pyruvate energy output 2 ATP net ethanol formation 2 H2O 2 CO2 2 acetaldehyde electrons, hydrogen from NADH 2 ethanol Fig. 8-10d, p.132

  35. Lactate Fermentation glycolysis C6H12O6 ATP 2 energy input 2 ADP 2 NAD+ 2 NADH 4 ATP 2 pyruvate energy output 2 ATP net lactate fermentation electrons, hydrogen from NADH 2 lactate Fig. 8-11, p.133

  36. Anaerobic Electron Transport • Carried out by certain bacteria • Electron transfer chain is in bacterial plasma membrane • Final electron acceptor is compound from environment (such as nitrate), not oxygen • ATP yield is low

  37. Summary of Energy Harvest(per molecule of glucose) • Glycolysis • 2 ATP formed by substrate-level phosphorylation • Krebs cycle and preparatory reactions • 2 ATP formed by substrate-level phosphorylation • Electron transport phosphorylation • 32 ATP formed

  38. Energy Harvest Varies • NADH formed in cytoplasm cannot enter mitochondrion • It delivers electrons to mitochondrial membrane • Membrane proteins shuttle electrons to NAD+ or FAD inside mitochondrion • Electrons given to FAD yield less ATP than those given to NAD+

  39. Efficiency of Aerobic Respiration • 686 kcal of energy are released • 7.5 kcal are conserved in each ATP • When 36 ATP form, 270 kcal (36 X 7.5) are captured in ATP • Efficiency is 270 / 686 X 100 = 39 percent • Most energy is lost as heat

  40. Alternative Energy Sources FOOD complex carbohydrates fats glycogen proteins simple sugars (e.g., glucose) fatty acids amino acids glycerol NH3 carbon backbones glucose-6-phosphate urea PGAL glycolysis 4 2 ATP ATP (2 ATP net) NADH pyruvate acetyl-CoA CO2 NADH Krebs Cycle NADH, FADH2 2 ATP CO2 e– ATP ATP electron transfer phosphorylation ATP many ATP water H+ e– + oxygen Fig. 8-13b, p.135

  41. Evolution of Metabolic Pathways • When life originated, atmosphere had little oxygen • Earliest organisms used anaerobic pathways • Later, noncyclic pathway of photosynthesis increased atmospheric oxygen • Cells arose that used oxygen as final acceptor in electron transport

  42. Processes Are Linked p.136b

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