Pyruvate oxidation

Summary: Stage 2 – Pyruvate Oxidation

1. Location:

• Occurs in the mitochondrial matrix after pyruvate is transported through the mitochondrial membranes.

2. Key Steps:

• Decarboxylation:

• A low-energy carboxyl group is removed from pyruvate as CO₂.

• Catalyzed by pyruvate decarboxylase.

• Oxidation:

• The remaining two-carbon compound is oxidized to form acetate.

• NAD⁺ is reduced to NADH by gaining two hydrogen atoms (2 protons, 2 electrons).

• Formation of Acetyl-CoA:

• Coenzyme A (CoA) binds to acetate, forming acetyl-CoA.

• The carbon-sulfur bond in acetyl-CoA is unstable, preparing it for further oxidation in the Krebs cycle.

3. Overall Equation:

4. Fates of Products:

• Acetyl-CoA: Enters the Krebs cycle for further energy transfer.

• NADH: Moves to the electron transport chain for ATP production.

• CO₂: Diffuses out of the mitochondrion and cell as waste.

• H⁺ ions: Remain dissolved in the matrix.

5. Role of Acetyl-CoA:

• Central to energy metabolism.

• Can either:

• Enter the Krebs cycle to produce ATP if ATP levels are low.

• Be used in lipid synthesis if ATP levels are high (energy storage).

6. Significance:

• All nutrients (proteins, lipids, carbohydrates) are ultimately converted into acetyl-CoA.

• Acetyl-CoA acts as a metabolic crossroad, directing energy toward immediate ATP production or fat storage based on the cell’s energy needs.

7. Energy and Fat Accumulation:

• Excess consumption of nutrients leads to fat accumulation, as acetyl-CoA is diverted into lipid synthesis when ATP levels are sufficient.

Stage 2 – Pyruvate Oxidation

Location: Occurs in the mitochondrial matrix after pyruvate is transported through the mitochondrial membranes.

Key Steps:

1. Decarboxylation: Low-energy carboxyl group is removed from pyruvate as CO₂, catalyzed by pyruvate decarboxylase.

2. Oxidation: The two-carbon compound is oxidized to form acetate, reducing NAD⁺ to NADH.

3. Formation of Acetyl-CoA: Acetyl-CoA is formed when Coenzyme A (CoA) binds to acetate, with the carbon-sulfur bond being unstable for further oxidation in the Krebs cycle.

Overall Fate of Products:

• Acetyl-CoA: Enters Krebs cycle for ATP production.

• NADH: Moves to the electron transport chain for ATP production.

• CO₂: Diffuses out as waste.

• H⁺ ions: Remain in the mitochondrial matrix.

Role of Acetyl-CoA:

• Central to energy metabolism, directing energy toward ATP production or lipid synthesis depending on energy needs.

Significance:

• Nutrients (proteins, lipids, carbohydrates) convert to acetyl-CoA, acting as a metabolic crossroad based on the cell’s energy requirements. Excess nutrients lead to fat accumulation when ATP levels are sufficient.