Glycolysis and the link reaction
Aerobic respiration: the first stages
- Aerobic respiration (with oxygen) runs in four stages.
- Each happens in a set place in the cell.
- We start with glycolysis and the link reaction.
Where each stage happens
| Stage | Location |
|---|---|
| glycolysis | the cytoplasm |
| link reaction | the matrix of the mitochondria |
| Krebs cycle | the matrix of the mitochondria |
| oxidative phosphorylation | the inner membrane of the mitochondria |
Practice
Match each stage of aerobic respiration to where it happens.
Glycolysis = cytoplasm; link reaction & Krebs = matrix; oxidative phosphorylation = inner membrane.
Glycolysis
- In the cytoplasm, glucose (6C) is phosphorylated using 2 ATP, then split into two triose phosphate (3C) molecules.
- These are oxidised to two pyruvate (3C).
- Net result: a gain of 2 ATP and some reduced NAD (NAD is a coenzyme, a helper molecule).
Practice
The net yield of glycolysis is:
Glycolysis uses 2 ATP and makes 4, a net gain of 2 ATP, plus reduced NAD.
Practice
Glycolysis ends by splitting glucose into:
Glucose (6C) → 2 triose phosphate (3C) → 2 pyruvate (3C).
The link reaction
- When oxygen is available, pyruvate enters the mitochondrial matrix.
- Each pyruvate loses a CO₂ and becomes a 2-carbon acetyl group.
- Carried by coenzyme A, it forms acetyl coenzyme A; NAD is reduced.
Practice
In the link reaction, each pyruvate:
Pyruvate is decarboxylated (loses CO₂) to a 2C acetyl group, carried by coenzyme A as acetyl CoA.
You've got it
Key idea
- aerobic respiration = 4 stages: glycolysis (cytoplasm), link + Krebs (matrix), oxidative phosphorylation (inner membrane)
- glycolysis: glucose → 2 pyruvate; net 2 ATP + reduced NAD
- link reaction: pyruvate → acetyl CoA (loses CO₂, reduces NAD)