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How Cells Release Chemical Energy

How Cells Release Chemical Energy. Chapter 8 Hsueh-Fen Juan Oct. 9, 2012. Video: When mitochondria spin their wheels. Impacts, Issues: When Mitochondria Spin Their Wheels.

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How Cells Release Chemical Energy

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  1. How Cells Release Chemical Energy Chapter 8 Hsueh-Fen Juan Oct. 9, 2012

  2. Video: When mitochondria spin their wheels

  3. Impacts, Issues:When Mitochondria Spin Their Wheels • More than forty disorders related to defective mitochondria are known (such as Friedreich’s ataxia); many of those afflicted die young Leah: A professional model

  4. 8.1 Overview of Carbohydrate Breakdown Pathways • Photoautotrophs make ATP during photosynthesis and use it to synthesize glucose and other carbohydrates • Most organisms, including photoautotrophs, make ATP by breaking down glucose and other organic compounds

  5. Comparison of the Main Pathways • Aerobic respiration • Aerobic metabolic pathways (using oxygen) are used by most eukaryotic cells • Fermentation • Anaerobic metabolic pathways (occur in the absence of oxygen) are used by prokaryotes and protists in anaerobic habitats

  6. Comparison of the Main Pathways • Aerobic respiration and fermentation both begin with glycolysis, which converts one molecule of glucose into two molecules of pyruvate • After glycolysis, the two pathways diverge • Fermentation is completed in the cytoplasm, yielding 2 ATP per glucose molecule • Aerobic respiration is completed in mitochondria, yielding 36 ATP per glucose molecule

  7. Comparison of the Main Pathways

  8. Animation: Where pathways start and finish

  9. Overview of Aerobic Respiration • Three stages • Glycolysis • Acetyl-CoA formation and Krebs cycle • Electron transfer phosphorylation (ATP formation) C6H12O6 (glucose) + O2 (oxygen) → CO2 (carbon dioxide) + H2O (water) • Coenzymes NADH and FADH2 carry electrons and hydrogen

  10. Overview of Aerobic Respiration

  11. Fig. 8-3b, p. 125

  12. Animation: Overview of aerobic respiration

  13. 8.1 Key Concepts:Energy From Carbohydrate Breakdown • Various degradative pathways convert the chemical energy of glucose and other organic compounds to the chemical energy of ATP • Aerobic respiration yields the most ATP from each glucose molecule; in eukaryotes, it is completed inside mitochondria

  14. 8.2 Glycolysis – Glucose Breakdown Starts • Glycolysis starts and ends in the cytoplasm of all prokaryotic and eukaryotic cells • An energy investment of ATP starts glycolysis

  15. Glycolysis • Two ATP are used to split glucose and form 2 PGAL, each with one phosphate group • Enzymes convert 2 PGAL to 2 PGA, forming 2 NADH • Four ATP are formed by substrate-level phosphorylation (net 2 ATP)

  16. Glycolysis

  17. Fig. 8-4a (2), p. 126

  18. Fig. 8-4b (1), p. 127

  19. Fig. 8-4b (2), p. 127

  20. The Balanced Chemical Equation for the Conversion of Glucose to Pyruvate

  21. The Glycolytic Pathway by Which Glucose is Degraded to Pyruvate (1)

  22. The Glycolytic Pathway by Which Glucose is Degraded to Pyruvate (2)

  23. The Glycolytic Pathway by Which Glucose is Degraded to Pyruvate (3)

  24. The Glycolytic Pathway by Which Glucose is Degraded to Pyruvate (4&5)

  25. The Glycolytic Pathway by Which Glucose is Degraded to Pyruvate (6)

  26. The Glycolytic Pathway by Which Glucose is Degraded to Pyruvate (7)

  27. The Glycolytic Pathway by Which Glucose is Degraded to Pyruvate (8)

  28. The Glycolytic Pathway by Which Glucose is Degraded to Pyruvate (9)

  29. The Glycolytic Pathway by Which Glucose is Degraded to Pyruvate (10)

  30. 8.2 Key Concepts:Glycolysis • Glycolysis is the first stage of aerobic respiration and of anaerobic routes such as fermentation pathways • Enzymes of glycolysis convert glucose to pyruvate

  31. 8.3 Second Stage of Aerobic Respiration • The second stage of aerobic respiration finishes breakdown of glucose that began in glycolysis • Occurs in mitochondria • Includes two stages: acetyl CoA formation and the Krebs cycle (each occurs twice in the breakdown of one glucose molecule)

  32. Acetyl CoA Formation • In the inner compartment of the mitochondrion, enzymes split pyruvate, forming acetyl CoA and CO2 (which diffuses out of the cell) • NADH is formed

  33. The Krebs Cycle • Krebs cycle • A sequence of enzyme-mediated reactions that break down 1 acetyl CoA into 2 CO2 • Oxaloacetate is used and regenerated • 3 NADH and 1 FADH2 are formed • 1 ATP is formed

  34. Inside a Mitochondrion

  35. Fig. 8-5a, p. 128

  36. Fig. 8-5b, p. 128

  37. Animation: Functional zones in mitochondria

  38. Acetyl CoA Formation and the Krebs Cycle

  39. Animation: The Krebs Cycle - details

  40. 8.4 Aerobic Respiration’s Big Energy Payoff • Many ATP are formed during the third and final stage of aerobic respiration • Electron transfer phosphorylation • Occurs in mitochondria • Results in attachment of phosphate to ADP to form ATP

  41. Electron Transfer Phosphorylation • Coenzymes NADH and FADH2 donate electrons and H+ to electron transfer chains • Active transport forms a H+ concentration gradient in the outer mitochondrial compartment • H+ follows its gradient through ATP synthase, which attaches a phosphate to ADP • Finally, oxygen accepts electrons and combines with H+, forming water

  42. Electron Transfer Phosphorylation

  43. Summary: The Energy Harvest • Typically, the breakdown of one glucose molecule yields 36 ATP • Glycolysis: 2 ATP • Acetyl CoA formation and Krebs cycle: 2 ATP • Electron transfer phosphorylation: 32 ATP

  44. Summary: Aerobic Respiration

  45. Animation: Third-stage reactions In brain and skeletal muscle cells, the yield is 38 ATP. In liver, heart, and kidney cells, it is 36 ATP.

  46. 8.3-8.4 Key Concepts:How Aerobic Respiration Ends • The final stages of aerobic respiration break down pyruvate to CO2 • Many coenzymes that become reduced deliver electrons and hydrogen ions to electron transfer chains; energy released by electrons flowing through the chains is captured in ATP • Oxygen accepts electrons at ends of the chains

  47. 8.5 Anaerobic Energy-Releasing Pathways • Fermentation pathways break down carbohydrates without using oxygen • The final steps in these pathways regenerate NAD+ but do not produce ATP

  48. Fermentation Pathways • Glycolysis is the first stage of fermentation • Forms 2 pyruvate, 2 NADH, and 2 ATP • Pyruvate is converted to other molecules, but is not fully broken down to CO2 and water • Regenerates NAD+ but doesn’t produce ATP • Provides enough energy for some single-celled anaerobic species

  49. Two Pathways of Fermentation • Alcoholic fermentation • Pyruvate is split into acetaldehyde and CO2 • Acetaldehyde receives electrons and hydrogen from NADH, forming NAD+ and ethanol • Lactate fermentation • Pyruvate receives electrons and hydrogen from NADH, forming NAD+ and lactate

  50. Two Pathways of Fermentation

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