Glycolysis and Krebs Cycle Overview

Glycolysis

• Process where glucose is broken down into two pyruvate molecules.
• Occurs in the cytoplasm of the cell.

Conversion of Pyruvate to Acetyl CoA

• Pyruvate, a three-carbon molecule, is converted into acetyl CoA, a two-carbon fragment.
• Occurs in the mitochondrion.
• During this conversion:
  • Carbon dioxide (CO2) is produced.
  • A molecule of NADH is formed.

Krebs Cycle (Citric Acid Cycle)

• Acetyl CoA enters the Krebs cycle.
• The cycle occurs in the mitochondrion.

Steps of the Krebs Cycle:

1. Formation of Six-carbon Compound:

   • Two-carbon acetyl portion of acetyl CoA is transferred to a four-carbon molecule, forming a six-carbon compound.
   • The CoA carrier molecule is released.

2. Decarboxylation and Oxidation:

   • Carbon dioxide is released, forming a five-carbon compound.
   • Hydrogen is removed and transferred to NAD+ to form NADH.

3. Second Oxidation and Decarboxylation:

   • Further production of NADH and CO2.
   • ATP is generated.
   • A four-carbon molecule is formed.

4. Regeneration of Four-carbon Molecule:

   • Further oxidation occurs.
   • Hydrogens removed are used to form NADH and FADH2.
   • Regenerates the original four-carbon molecule that reacts with acetyl CoA.

Overall Cycle and Energy Yield

• For each glucose molecule, two pyruvate molecules are produced during glycolysis.
• Each pyruvate is converted to acetyl CoA, entering the Krebs cycle.
• Therefore, for every glucose molecule, the Krebs cycle must complete two circuits.
• The cycle produces:
  • NADH
  • FADH2
  • CO2
  • ATP