Question

From the following options, identify the 5C intermediate compound in the TCA cycle.

• A. Citric acid
• B. Succinyl CoA
• C. $\alpha$-ketoglutaric acid
• D. Fumaric acid

Answer 1

The correct option is C $\alpha$-ketoglutaric acid

The TCA cycle or Krebs’ cycle starts with the condensation of acetyl group with oxaloacetic acid (4C) (OAA) and water to yield citric acid (6C). The reaction is catalysed by the enzyme citrate synthase and a molecule of CoA is released. Citrate is then isomerised to isocitrate (6C). It is followed by dehydrogenation leading to the formation of oxalosuccinate. This undergoes oxidative decarboxylation leading to the formation of $\alpha$-ketoglutarate. It is a 5C intermediate molecule in the TCA cycle.