Lecture: Bioenergetics and Aerobic Respiration

Overview

• Focus on aerobic respiration following glycolysis.
• Examines the path of glycolysis products, specifically pyruvate.

Pyruvate Pathway

• Glycolysis produces 2 pyruvate molecules in the cytosol.
• Path of pyruvate depends on oxygen presence:
  • High Oxygen:
    • Pyruvate enters mitochondria.
    • Undergoes Krebs cycle (to be discussed).
  • Low Oxygen:
    • Pyruvate undergoes fermentation.
    • Example: During strenuous exercise, oxygen is depleted leading to fermentation.

Pyruvate Oxidation

• Takes place within mitochondria using a symport transport protein.
• Process Details:
  • Pyruvate oxidized to Acetyl-CoA.
  • Enzyme: Pyruvate dehydrogenase complex.
  • Conversion involves:
    • Reduction of NAD+ to NADH.
    • Release of CO2.

Krebs Cycle (Citric Acid Cycle)

• Occurs in mitochondrial matrix.
• Each glucose molecule results in two cycles of Krebs.
• Cycle Steps and Reactions:
  1. Acetyl-CoA + Oxaloacetate → Citrate
     • Enzyme: Citrate synthase.
  2. Citrate → Isocitrate
     • Enzyme: Aconitase.
  3. Isocitrate → α-Ketoglutarate
     • Produces CO2.
     • Enzyme: Isocitrate dehydrogenase.
     • NAD+ reduced to NADH.
  4. α-Ketoglutarate → Succinyl-CoA
     • Produces CO2.
     • Enzyme: α-Ketoglutarate dehydrogenase.
     • NAD+ reduced to NADH.
  5. Succinyl-CoA → Succinate
     • Release of CoA.
     • Conversion of GDP to GTP, then ATP.
  6. Succinate → Fumarate
     • Enzyme: Succinate dehydrogenase.
     • FAD reduced to FADH2.
  7. Fumarate → Malate
     • Enzyme: Fumarase.
  8. Malate → Oxaloacetate
     • Enzyme: Malate dehydrogenase.
     • NAD+ reduced to NADH.

Products Per Acetyl-CoA

• 3 NADH
• 1 FADH2
• 1 ATP

Conclusion and Next Steps

• The lecture splits into two parts.
• Next lecture will cover the electron transport chain and ATP production through oxidative phosphorylation and chemiosmosis.