Pyruvate Decarboxylation/Pyruvate Oxidation + Citric Acid Cycle/Krebs Cycle/Tricarboxylic Acid Cycle + Beta Oxidation

Pyruvate Ox. + TCA + Beta Oxidation

Where does Citric Acid Cycle/Krebs Cycle/Tricarboxylic Acid Cycle occur?

eukaryotes

• mitochondrial matrix

prokaryotes

• cytosol

Products of Citric Acid Cycle/Krebs Cycle/Tricarboxylic Acid Cycle

1 FADH2, 3 NADH, 1 GTP/ATP, 2 CO2, and acetyl-CoA derivatives

What happens to Acetyl-CoA?

1. Acetyl-CoA (2C) + Oxaloacetate (4C) = Citrate (6C)

• Enzyme: Citrate Synthase

What happens to Citrate?

2. Citrate → Isocitrate

• Enzyme: Aconitase

What happens to Isocitrate?

3. Isocitrate → α-Ketoglutarate (5C) + CO₂

• Loses CO₂

• NAD⁺ → NADH

• Enzyme: Isocitrate dehydrogenase

  • Rate-limiting step

What happens to α-Ketoglutarate?

4. α-Ketoglutarate (5C) → Succinyl-CoA (4C) + CO₂

• Loses CO₂

• NAD⁺ → NADH

• Enzyme: α-Ketoglutarate dehydrogenase

What happens to Succinyl-CoA?

5. Succinyl-CoA (4C)→ Succinate

• ADP → ATP

• Enzyme: Succinyl-CoA synthetase

What happens to Succinate?

6. Succinate → Fumarate

• FAD → FADH₂

• Enzyme: Succinate dehydrogenase

What happens to Fumarate?

7. Fumarate → Malate

• Enzyme: Fumarase

What happens to Malate?

8. Malate → Oxaloacetate

• NAD → NADH

• Enzyme: Malate dehydrogenase (MDH)

Where does Pyruvate Decarboxylation/Pyruvate Oxidation Occur?

Mitochondrial Matrix

What happens in Pyruvate Decarboxylation/Pyruvate Oxidation?

• 3 carbon pyruvate enters the mitochondria

• Pyruvate is decarboxylated, forming acetyl group

  • CO2 is released producing a 2 carbon acetyl and providing electrons that reduce NAD⁺ to NADH

• CoA binds the remaining acetyl group and produces acetyl-CoA

Where does Beta Oxidation occur?

mitochondrial matrix

What happens during Beta Oxidation?

• Beta Oxidation — energy from fats

  • Requires ATP (activation energy)

    • Fatty acid + CoA + energy → Fatty acyl CoA (Activated)

  • Beta-oxidation cycle

  • Then it can undergo a series of cleavages into acetyl-CoA molecules

    • Also converts FAD & NAD⁺ into FADH & NADH

• Products: 1 NADH, 1 FADH₂, and 1 acetyl-CoA molecule

  • Does NOT make ATP