Q. In citric acid cycle the step which is not mediated by dehydrogenase enzyme is :

A. Oxaloacetic acid to citric acid

B. Citric acid to a-ketoglutaric acid

C. Succinic acid to fumaric acid

D. Malic acid to oxaloacetic acid

Correct Answer : Option A

Solution

Malic acid converts into oxaloacetate in the presence of Malic dehydrogenase.Succinate converts into fumarate in the presence of Succinic dehydrogenase.Oxaloacetic acid forms citric acid in the presence of enzyme citrate synthetase.Citric acid converts into alpha-ketoglutarate in stepwise reactions.
So the correct option is ‘Oxaloacetate to citric acid’.