Overview
This lecture explains the link reaction in aerobic respiration, detailing its steps, products, and why it is called oxidative decarboxylation.
Glycolysis Recap
- Glycolysis occurs in the cytoplasm and breaks down glucose (6C) into two pyruvate molecules (3C each).
- Glycolysis produces a net gain of 2 ATP and 2 reduced NAD molecules.
- Pyruvate still contains significant stored energy.
Aerobic Respiration and Mitochondria
- If oxygen is present, aerobic respiration follows glycolysis.
- The remaining respiration stages occur in the mitochondria, specifically in the mitochondrial matrix.
- Pyruvate is actively transported from the cytoplasm into the mitochondrial matrix.
The Link Reaction
- Pyruvate (3C) reacts with coenzyme A in the mitochondrial matrix.
- A 2-carbon group from pyruvate binds to coenzyme A, forming acetyl coenzyme A.
- The remaining 1-carbon is released as carbon dioxide (COâ‚‚).
- Simultaneously, an oxidation reaction produces reduced NAD (NADH).
- Products per pyruvate: 1 acetyl coenzyme A, 1 COâ‚‚, and 1 reduced NAD.
- For each glucose (2 pyruvate): 2 acetyl coenzyme A, 2 COâ‚‚, and 2 reduced NAD formed.
Oxidative Decarboxylation
- Removal of COâ‚‚ from pyruvate is called decarboxylation.
- Formation of reduced NAD is an oxidation reaction.
- The link reaction is both an oxidation and decarboxylation, termed oxidative decarboxylation.
- The link reaction does not require oxygen.
Key Terms & Definitions
- Glycolysis — Breakdown of glucose into pyruvate in the cytoplasm.
- Pyruvate — 3-carbon molecule produced from glycolysis.
- Coenzyme A — Molecule that combines with a 2-carbon group to form acetyl coenzyme A.
- Acetyl Coenzyme A — 2-carbon molecule that enters the Krebs cycle.
- Decarboxylation — Removal of a carbon dioxide molecule.
- Oxidative Decarboxylation — Simultaneous oxidation and decarboxylation in a single reaction.
Action Items / Next Steps
- Review the steps and products of the link reaction.
- Prepare for the next lesson on the Krebs cycle.