Question

Explain the reactions of tricarboxylic acid (TCA) cycle and its role in energy production.

Answer 1

the TCA starts with condensation of acetyl group with oxaloacetic acid and water to yield citric acid. the reaction is catalysed by the enzyme citric synthase and a molecule of CoA is released. citrate is then isomerised to isocitrate. it is followed by two successive steps of decarboxylation leading to the formation of alpha ketoglutaric acid and then succinyl CoA. in the remaining steps of citric acid cycle, succinyl CoA is oxidised to OAA. during conversion of succinyl CoA to succinic acid a molecule of GTP is synthesised. this is a substrate level of phosphorylation. in a coupled reaction GTP is converted to GDP with the simultaneous synthesis of ATP from ADP. also there are three points in the cycle where NAD+ is reduced to NADH + H+ and one point where FAD+ is reduced to FADH2 . the continued oxidation of acetyl CoA via the TCA cycle requires continued replenishment of oxaloacetic acid, the first member of the cycle. in addition it also requires regeneration of. NAD+ and FAD+ from NADH and. FADH2 respectively.