Tricarboxylic acid cycle
- Kreb’s cycle takes place in the mitochondrial matrix.
- Several intermediate compounds are formed, which contain three carboxylic groups and therefore the process is called as tricarboxylic acid cycle (TCA).
- First, the condensation of acetyl group with oxaloacetic acid (OAA) and water takes place to yield citric acid, catalysed by the enzyme citrate synthase and a molecule of CoA is released.
- Citrate is then isomerised to isocitrate, which is followed by two successive steps of decarboxylation, leading to the formation of α-ketoglutaric acid and then succinyl-CoA.
- Succinyl-CoA is oxidised to OAA allowing the cycle to continue and during the conversion of succinyl-CoA to succinic acid a molecule of GTP is synthesised.
- In a coupled reaction, GTP is converted to GDP with the simultaneous synthesis of ATP from ADP.
Pyruvic acid + 4 NAD+ + FAD+ + 2H2O + ADP + Pi à 3CO2 + 4NADH + 4H+ + FADH2 + ATP
- During the process, 8NADH2, 2FADH2, 2 GTPs are formed.
Fig. Krebs cycle