Math Simplified: Krebs Cycle

Overview

• The Krebs Cycle, also known as the Tricarboxylic Acid Cycle (TCA), is a biochemical pathway for energy generation.
• It involves the oxidation of Acetyl-CoA and is crucial for the synthesis of NADH and amino acids.
• Occurs in the mitochondria of eukaryotes and the cytosol of prokaryotes.

Preparatory Step

• Begins with pyruvate, derived from glycolysis (splitting of glucose).
• Glucose (6-carbon) splits into two pyruvate molecules (3-carbon each).
• Pyruvate is oxidized to Acetyl-CoA by the enzyme pyruvate dehydrogenase complex, producing:
  • 1 molecule of CO2
  • 1 molecule of NADH

Steps of the Krebs Cycle

1. Formation of Citrate

   • Acetyl-CoA (2-carbon) combines with oxaloacetate (4-carbon) to form citrate (6-carbon).
   • Catalyzed by the enzyme citrate synthase.

2. Isomerization of Citrate

   • Citrate is isomerized into isocitrate by the enzyme aconitase.

3. Formation of α-Ketoglutarate

   • Isocitrate is oxidized to α-ketoglutarate (5-carbon) by isocitrate dehydrogenase.
   • Produces:
     • 1 molecule of NADH
     • 1 molecule of CO2

4. Formation of Succinyl-CoA

   • α-Ketoglutarate is converted to succinyl-CoA (4-carbon) by α-ketoglutarate dehydrogenase.
   • Produces:
     • 1 molecule of NADH
     • 1 molecule of CO2

5. Formation of Succinate

   • Succinyl-CoA is converted into succinate by the enzyme succinyl-CoA synthetase.
   • Produces 1 molecule of GTP.

6. Formation of Fumarate

   • Succinate is converted to fumarate by succinate dehydrogenase.
   • Produces 1 molecule of FADH2.

7. Formation of Malate

   • Fumarate is converted into malate by the enzyme fumarase.

8. Regeneration of Oxaloacetate

   • Malate is converted back to oxaloacetate by malate dehydrogenase.
   • Produces 1 molecule of NADH.

Products of the Krebs Cycle

• For each cycle, the following products are generated:
  • 3 NADH
  • 1 FADH2
  • 1 GTP
  • 2 CO2
• Because glucose generates two pyruvate molecules, the cycle runs twice per glucose molecule, resulting in:
  • 6 NADH
  • 2 FADH2
  • 2 GTP
  • 4 CO2

Role in ATP Production

• NADH and FADH2 are fed into the electron transport chain to produce ATP.

Conclusion

• This was a brief overview of the Krebs Cycle.

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