5.2.4 The Link Reaction

What is the Link Reaction?

• The link reaction connects glycolysis to the Krebs cycle in aerobic respiration.
• It occurs in the mitochondrial matrix.

Steps of the Link Reaction

1. Transport of Pyruvate:

• The two molecules of pyruvate (3C) produced in glycolysis are actively transported into the mitochondrial matrix.

2. Decarboxylation of Pyruvate:

• The enzyme pyruvate decarboxylase removes one molecule of carbon dioxide (CO₂) from each pyruvate.
• This forms a 2-carbon molecule called acetate.

3. Oxidation of Acetate:

• During decarboxylation, hydrogen is removed from pyruvate and used to reduce NAD to NADH (reduced NAD).

4. Formation of Acetyl Coenzyme A:

• The acetate combines with coenzyme A (CoA) to form acetyl coenzyme A (acetyl CoA).

Products Per Glucose Molecule

• 2 Acetyl CoA: Enters the Krebs cycle.
• 2 NADH: Used in oxidative phosphorylation to generate ATP.
• 2 CO₂: Released as a waste product.
• No ATP is directly produced in this stage.

Reaction Summary

The link reaction can be summarised as:

Pyruvate (3C) + CoA + NAD → Acetyl CoA (2C) + CO₂ + NADH