Expansion
Glycolysis, the Krebs cycle and oxidative phosphorylation
Expansion
| Stage | Site | Oxygen needed | Net ATP per glucose |
|---|---|---|---|
| Glycolysis | Cytoplasm | No | 2 (plus 2 NADH) |
| Pyruvate to acetyl-CoA | Mitochondrion | Yes | (2 NADH) |
| Krebs cycle | Mitochondrial matrix | Yes | 2 GTP (plus 6 NADH, 2 FADH2) |
| Oxidative phosphorylation | Inner mitochondrial membrane | Yes | about 26 |
| Total | about 30 to 32 |
Without oxygen, pyruvate is converted to lactate to regenerate NAD+ so that glycolysis can continue, yielding only 2 ATP.
Consequences of this arithmetic:
- Cells wholly dependent on glycolysis, such as red cells (no mitochondria) and the renal medulla, are highly vulnerable
- Tissues with high energy demand and many mitochondria, such as heart and brain, fail rapidly without oxygen
- Fat yields far more ATP per gram but requires oxygen throughout, which is why it cannot fuel maximal exercise
Cyanide blocks cytochrome oxidase, and dinitrophenol uncouples the chain, producing heat instead of ATP.