Glycolysis and Citric Acid Cycle

Overview

• Glycolysis occurs in the cytoplasm, converting glucose into two pyruvate molecules.
• Pyruvate is transported into the mitochondrial matrix and converted to acetyl Coenzyme A (acetyl CoA), linking glycolysis with the citric acid cycle.

Pyruvate to Acetyl CoA Conversion

• Transport: Pyruvate enters the mitochondrial matrix using a carrier protein.
• Oxidation: Pyruvate is oxidized to acetyl CoA by the enzyme pyruvate dehydrogenase.
  • Produces carbon dioxide (CO2).
  • Converts NAD+ to NADH (not shown in the diagram for clarity).

Citric Acid Cycle (Krebs Cycle)

• Purpose: Harvests chemical energy, producing three NADH molecules per cycle.
• Key Steps:
  1. Citrate Synthesis:
     • Acetyl CoA combines with oxaloacetate to form citrate.
  2. Isomerization:
     • Citrate is converted to isocitrate by aconitase.
  3. First Oxidation:
     • Isocitrate is oxidized to alpha-ketoglutarate, releasing CO2 and forming NADH.
  4. Second Oxidation:
     • Alpha-ketoglutarate is oxidized to succinyl CoA, releasing CO2 and forming NADH.
  5. GTP Production:
     • Succinyl CoA is converted to succinate, releasing CoA and forming GTP.
  6. Succinate Oxidation:
     • Succinate is oxidized to fumarate by succinate dehydrogenase.
     • Succinate dehydrogenase is part of the electron transport chain (Complex 2).
     • FAD is used instead of NAD+ to accept electrons.
  7. Fumarate to Malate:
     • Fumarate is converted to malate by fumarase.
  8. Malate Oxidation:
     • Malate is oxidized to reform oxaloacetate, converting NAD+ to NADH.

Additional Notes

• Complex 2 Role:
  • Transfers electrons to coenzyme Q and further to Complex 3 in the electron transport chain.
• Regeneration of Oxaloacetate:
  • Allows continuous operation of the cycle by combining with new acetyl CoA.