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Energy-Releasing Pathways: Anaerobic and Aerobic Cellular Respiration

This chapter covers the main types of energy-releasing pathways in cellular respiration, detailing anaerobic and aerobic processes. Anaerobic pathways, which evolved first, do not require oxygen and occur in the cytoplasm, yielding a net gain of 2 ATP per glucose molecule. In contrast, aerobic pathways evolved later, necessitating oxygen and progressing from the cytoplasm to the mitochondria, generating a total of up to 36 ATP per glucose molecule through glycolysis, the Krebs cycle, and electron transport phosphorylation. Additionally, it discusses the importance of insulin and diabetes types that affect glucose metabolism.

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Energy-Releasing Pathways: Anaerobic and Aerobic Cellular Respiration

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  1. How Cells Release Chemical Energy Chapter 6

  2. Main Types of Energy-Releasing Pathways Anaerobic pathways • Evolved first • Don’t require oxygen • All reactions take place in the cytoplasm Aerobic pathways • Evolved later • Requires oxygen • Reactions start in the cytoplasm and finish in the mitochondria

  3. Summary Equation for Aerobic Respiration C6H12O6 + 6O2 6CO2 + 6H2O + ATP GLUCOSE OXYGEN WATER CARBON DIOXIDE

  4. 3 Steps of Aerobic Respiration Glycolysis --- Uses: Glucose, 2 ATP, 2 NAD+ --- Makes: 2 Pyruvate, 4 ATP, 2 NADH Krebs Cycle ---Uses: 2 Pyruvate, 6 NAD+, 2 FAD ---Makes: 6 CO2, 2 ATP, 6 NADH, 2 FADH2

  5. Glycolysis: Net Energy Yield Energy requiring steps: 2 ATP used Energy releasing steps: 2 NADH formed 4 ATP formed Net yield: 2 ATP + 2 NADH

  6. Mitochondria

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

  8. ATP O O =CoA Krebs Cycle acetyl-CoA CoA oxaloacetate citrate H2O NADH NAD+ H2O Mitochondrion's Inner Compartment malate isocitrate NAD+ H2O O O NADH fumarate FADH2 a-ketoglutarate FAD NAD+ CoA NADH succinate succinyl-CoA ADP + phosphate group

  9. Results of the Second Stage • All of the carbon molecules in pyruvate eventually are released as Carbon Dioxide • Coenzymes pick up hydrogens and electrons • 2 ATP are formed

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

  11. Electron Transfer Phosphorylation • Occurs in Mitochondria • Coenzymes deliver electrons to electron transfer systems • Sets up H+ ion gradients • Gradients powers ATP formation • Requires Oxygen

  12. glucose ATP 2 2 NAD+ 2 PGAL ATP 4 2 NADH 2 pyruvate Glycolysis 2 FADH2 2 CO2 e– 2 acetyl-CoA oxygen accepts “spent” electrons 2 NADH H+ H+ 6 NADH 2 ATP Krebs Cycle ATP H+ 2 FADH2 ATP H+ 4CO2 ATP 32 H+ H+ ADP + Pi Electron Transfer phosphorylation H+ H+ H+ Fig. 6-5 p.87

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

  14. Fermentation Pathways • Begin with glycolysis • Are anaerobic: don’t require oxygen • Yield only 2 ATP from glycolysis • Steps after glycolysis only regenerate NAD+

  15. GLYCOLYSIS Alcoholic Fermentation C6H12O6 2 ATP 2 NAD+ energy input 2 ADP NADH 2 ATP 4 2 pyruvate energy output 2 ATP net ETHANOL FORMATION 2 H2O 2 CO2 2 acetaldehyde electrons, hydrogen from NADH 2 ethanol

  16. Lactate Fermentation GLYCOLYSIS C6H12O6 ATP 2 energy input 2 NAD+ 2 ADP NADH 2 ATP 4 2 pyruvate energy output 2 ATP net LACTATE FORMATION electrons, hydrogen from NADH 2 lactate

  17. sunlight energy photosynthesis organic compounds, oxygen carbon dioxide, water aerobic respiration p.92

  18. Importance of Insulin • Insulin is a __________ released by the pancreas when there is a high concentration of glucose in the blood. • It binds to cell receptors and tells the cells to take in glucose and start glycolysis.

  19. Diabetes • Type 1: (Juvenile onset) – Disease or condition prevents the pancreas from releasing insulin. (Treated by injecting insulin before meals) Type 2 (adult onset) – Cell receptors start to become insensitive to insulin. (treated by exorcise, weight loss, and some drugs)

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