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Metabolism
Metabolism
Metabolism
Metabolism
Metabolism
Metabolism
Metabolism
Metabolism
Metabolism
Metabolism
Metabolism
Metabolism
Metabolism
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Metabolism

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  • 1. Chapter 5 Cell Respiration and Metabolism
  • 2. Objectives
    • Explain the functional significance of the Kreb’s cycle in relation to the electron-transport system.
    • Describe the electron-transport system and oxidative phosphorylation.
    • Describe the role of oxygen in aerobic respiration.
    • Compare the lactic acid pathway and aerobic respiration in terms of initial substrates, final products, cellular locations, and the total number of ATP molecules produced per glucose respired.
  • 3. Metabolism
    • All reactions that involve energy transformations.
    • Divided into 2 categories:
      • Catabolic:
        • Release energy.
        • Breakdown larger organic molecules into smaller molecules.
        • Serve as primary sources of energy for synthesis of ATP.
      • Anabolic:
        • Require input of energy.
        • Synthesis of large energy-storage molecules.
  • 4. Glycolysis
    • Metabolic pathway by which glucose is converted to 2 molecules of pyruvic acid (pyruvate).
    • Glycolysis Pathway:
    • Glucose + 2 NAD + 2 ADP + 2 P i
    • 2 pyruvic acid + 2 NADH + 2 ATP
    Figure 5-1
  • 5. Glycolysis (continued)
    • Glycolysis is exergonic.
    • Glucose must be activated first before energy can be obtained.
      • ATP consumed at the beginning of glycolysis.
        • ATP ADP + P i
      • P i is not released but added to intermediate molecules (phosphorylation).
        • Phosphorylation of glucose, traps the glucose inside the cell.
    • Net gain of 2 ATP, 2 NADH, + 2 H + .
  • 6. Lactic Acid Pathway
    • Metabolic pathway by which glucose is converted to lactic acid (anaerobic respiration):
      • Oxygen is not used in the process.
    • NADH + H + + pyruvic acid lactic acid and NAD.
    • Produce 2 ATP/glucose molecule.
    Figure 5-3
  • 7. Lactic Acid Pathway (continued)
    • Some tissues better adapt to anaerobic conditions:
      • RBCs do not contain mitochondria and only use the lactic acid pathway.
      • Occurs in skeletal muscles and heart when ratio of oxygen supply to oxygen need falls below critical level.
        • Skeletal muscle:
          • Normal daily occurrence.
          • Does not harm muscle tissue.
        • Cardiac muscle normally respires aerobically:
          • Myocardial ischemia occurs under anaerobic conditions.
  • 8. Aerobic Respiration
    • The pyruvic acid formed by glycolysis enters interior of mitochondria.
    • Converted by coenzyme A to 2 molecules of acetyl CoA and 2 C0 2 .
    • Acetyl CoA serves as substrate for mitochondrial enzymes in the aerobic pathway.
    Figure 5-6
  • 9. Krebs Cycle (Citric Acid Cycle)
    • Acetyl CoA subunit combines with oxaloacetic acid to form citric acid.
    • Citric acid enters the Krebs Cycle.
      • Through a series of reactions, citric acid is converted to oxaloacetic acid to complete the pathway.
    • Produces:
    • 1 GTP, 3 NADH, and 1 FADH 2 , C0 2
      • NADH and FADH 2 transport electrons to Electron Transport System (ETC).
  • 10. Electron Transport and Oxidative Phosphorylation
    • Cristae of inner mitochondrial membrane contain molecules that serve as an electron transport system during aerobic respiration.
      • Electron transport chain consists of FMN, coenzyme Q, and cytochromes.
      • Each cytochrome transfers electron pairs from NADH and FADH 2 to next cytochrome.
        • Oxidized NAD and FAD are regenerated and shuttle electrons from the Krebs Cycle to the ETC.
    • Cytochrome receives a pair of electrons.
  • 11. Electron Transport
    • Cytochrome a 3 transfers electrons to O 2 (final electron acceptor).
    • Oxidative phosphorylation occurs:
      • Energy derived is used to phosphorylate ADP to ATP.
    Figure 5-9
  • 12. Coupling Electron Transport to to ATP Production
    • Chemiosmotic theory:
      • ETC (powered by transport of electrons) pumps H + from mitochondria matrix into the space between inner and outer mitochondrial membranes.
      • ETC grouped into 3 proton pumps:
        • NADH-coenzyme Q reductase complex:
          • Transports 4 H + for every pair of electrons into the intermembrane space for every pair of electrons.
        • Cytochrome C reductase complex:
          • Transports 4 H + into intermembrane space.
        • Cytochrome C oxidase complex:
          • Transports 2 H + into intermembrane space.
  • 13. Coupling Electron Transport to ATP Production (continued)
    • Oxygen functions as the last electron acceptor.
      • Oxidizes cytochrome a 3 .
    • Oxygen accepts 2 electrons.
    • O 2 + 4 e - + 4 H + 2 H 2 0
    Figure 5-10

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