Understanding the Krebs Cycle Process

Sep 2, 2024

Krebs Cycle Overview

Definition

  • Also known as the Tricarboxylic Acid Cycle (TCA Cycle).
  • Biochemical pathway used to generate energy through the oxidation of acetyl-CoA.
  • Involved in the synthesis of NADH and production of amino acids.

Location

  • Takes place in the mitochondria of eukaryotes.
  • Occurs in the cytosol of prokaryotes.

Steps of the Krebs Cycle

1. Preparatory Step

  • Starting Material: Pyruvate (3 carbon compound) derived from glycolysis of glucose (6 carbon compound).
  • Conversion: Pyruvate is oxidized into acetyl-CoA (2 carbon compound).
  • Enzyme: Pyruvate dehydrogenase complex.
  • Byproducts: 1 molecule of CO2 and 1 molecule of NADH generated.

2. Formation of Citrate

  • Reaction: Acetyl-CoA combines with oxaloacetate (4 carbon compound) to form citrate (6 carbon compound).
  • Enzyme: Citrate synthase.

3. Isomerization of Citrate

  • Conversion: Citrate is isomerized into isocitrate.
  • Enzyme: Aconitase.

4. Oxidation of Isocitrate

  • Conversion: Isocitrate is oxidized into alpha-ketoglutarate (5 carbon compound).
  • Enzyme: Isocitrate dehydrogenase.
  • Byproducts: 1 molecule of NADH and 1 molecule of CO2 generated.

5. Conversion of Alpha-Ketoglutarate

  • Reaction: Alpha-ketoglutarate is converted into succinyl-CoA (4 carbon compound).
  • Enzyme: Alpha-ketoglutarate dehydrogenase.
  • Byproducts: 1 molecule of NADH and 1 molecule of CO2 generated.

6. Conversion of Succinyl-CoA

  • Reaction: Succinyl-CoA is converted into succinate.
  • Enzyme: Succinyl-CoA synthetase.
  • Byproduct: 1 molecule of GTP generated.

7. Conversion of Succinate

  • Reaction: Succinate is converted into fumarate.
  • Enzyme: Succinate dehydrogenase.
  • Byproduct: 1 molecule of FADH2 generated.

8. Conversion of Fumarate

  • Reaction: Fumarate is converted into malate.
  • Enzyme: Fumarase.

9. Conversion of Malate

  • Reaction: Malate is converted into oxaloacetate.
  • Enzyme: Malate dehydrogenase.
  • Byproduct: 1 molecule of NADH generated.

Products of the Krebs Cycle

  • For each cycle:
    • 3 molecules of NADH
    • 1 molecule of FADH2
    • 1 molecule of GTP
    • 2 molecules of CO2
  • Since glucose yields two pyruvate, the cycle runs twice per glucose molecule:
    • Total: 6 NADH, 2 FADH2, 2 GTP, and 4 CO2.

Final Note

  • All NADH and FADH2 are fed into the electron transport chain for ATP generation.

Closing

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