the TCA Cycle

Pyruvate to Acetyl CoA

• Two pyruvates are moved into the mitochondrion.
• Inside the mitochondrion, they are converted into acetyl CoA.
• This conversion generates NADH, an energy intermediate.
• Two pyruvates result in two NADHs and two acetyl CoAs.

TCA Cycle (Krebs Cycle/Citric Acid Cycle)

• Acetyl CoAs enter the TCA cycle.
• The TCA cycle involves a series of reactions with specific enzymes and products.
• Detailed knowledge of this pathway, including enzymes and intermediates, is required.

Steps of the TCA Cycle

1. Citrate Formation

• Acetyl CoA combines with oxaloacetate.
• Enzyme: Citrate synthase.
• Product: Citrate.

2. Isocitrate Formation

• Citrate is converted to isocitrate.
• Enzyme: Aconitase.

3. Alpha-Ketoglutarate Formation

• Isocitrate is converted to alpha-ketoglutarate.
• Enzyme: Isocitrate dehydrogenase.
• Energy Generation: NADH is produced (two NADHs from two pyruvates).

4. Succinyl CoA Formation

• Alpha-ketoglutarate is converted to succinyl CoA.
• Enzyme: Alpha-ketoglutarate dehydrogenase.
• Energy Generation: NADH is produced.

5. Succinate Formation

• Succinyl CoA is converted to succinate.
• Enzyme: Succinyl CoA synthetase.
• Energy Generation: GTP is formed, which can be used to create ATP (two ATPs, one from each pyruvate).

6. Fumarate Formation

• Succinate is converted to fumarate.
• Enzyme: Succinate dehydrogenase.
• Energy Generation: FADH2 is produced (two FADH2).

7. Malate Formation

• Fumarate is converted to malate.
• Enzyme: Fumarate hydratase.

8. Oxaloacetate Regeneration

• Malate is converted back to oxaloacetate.
• Enzyme: Malate dehydrogenase.
• Energy Generation: NADH is produced (two NADHs).
• Cycle Regeneration: Oxaloacetate can combine with another molecule of Acetyl CoA, to repeat the cycle.

Energy Products in TCA Cycle

The TCA cycle produces:

• ATP (via GTP)
• NADH
• FADH2

These energy intermediates (NADH and FADH2) can be used to generate more ATP in the next stage.