Question

11. Which enzyme is NOT part of the TCA cycle?

A. Citrate synthase B. Succinate dehydrogenase C. alpha-ketoglutarate dehydrogenase D. Aconitase E. Pyruvate dehydrogenase

Answer 1

Ans 11) The correct answer is option "E" i.e pyruvate dehydrogenase.

Citrate synthase undergo condensation reaction of oxaloacetate and another molecule of Acetyl-CoA to form Citrate.

Succinate dehydrogenase undergo oxidation reaction of succinate into fumarate and FADH2 is produced during this step.

Alpha-ketoglutarate dehydrogenase undergo oxidative decarboxylation reaction to convert $\alpha$ -ketoglutarate into succinyl CoA and NADH is produced dusring this step.

Aconitase undergoes isomerization reaction of critrate into cis-aconitate by removal of water molecule.

Pyruvate dehydrogenase enzyme is not a part of Krebs cycle. Pyruvate + CoA in presence of pyruvate dehydrogenase complex forms Acetyl-CoA + Co2 . This is pyruvate oxidation (connecting link between glycolysis and krebs cycle) which occurs in mitochondrial matrix in Eukaryotes and in cytosol in Prokaryotes and requires oxygen.