Question

Oxidative decarboxylation occurs during the formation of
a. Citric acid and succinic acid
b. Citric acid and Oxaloacetic acid
c. Acetyl CoA and Succinyl CoA
d. Oxaloacetic acid and Oxalosuccinic acid

Answer 1

Hint: Oxidative decarboxylation or aerobic oxidation of pyruvic acid occurs in the mitochondria. The Pyruvic acid formed anaerobically in the cytoplasm can release energy only in aerobic conditions in the presence of enzymes present in the mitochondria.

Complete answer:
The oxidative decarboxylation of pyruvic acid in mitochondria forms acetyl CoA by the action of pyruvic acid dehydrogenase enzyme which is present in the mitochondrial matrix, through a series of reactions. The acetyl CoA acts as a connecting link between glycolysis and citric acid cycle. During this process two molecules of NADH are formed by breaking down two molecules of pyruvic acid.

Oxidative decarboxylation is one of the steps of Krebs’ cycle in which the isocitrate is followed by the removal of the carboxyl group as carbon dioxide (decarboxylation). It leads to the formation of alpha ketoglutaric acid in the presence of enzyme isocitrate hydrogenase and manganese ion which then forms succinyl CoA catalyzed by alpha complex.

The Citric acid cycle or Krebs’ cycle has the following steps:
- Condensation: It occurs in the presence of enzyme citric acid synthetase.
- Rearrangement: It occurs in the presence of enzyme aconitase.
- Dehydrogenation: It occurs in the presence of enzyme isocitrate dehydrogenase.
- Decarboxylation: It occurs in the presence of enzyme oxalosuccinate decarboxylase.
- Oxidative decarboxylation: It is completed in two steps.
- Dehydrogenation: Succinate dehydrogenase catalyzes this step.
- Hydration: Fumarase catalyzes this step.
- Dehydrogenation: Malate dehydrogenase catalyzes this step
So the oxidative decarboxylation occurs during the formation of Acetyl CoA and Succinyl CoA.

Hence, the correct answer is option (C).

Note: The oxidative decarboxylation involves the loss of two hydrogen atoms through dehydrogenation and loss of carbon dioxide molecule from the compound. The enzymes involved in this reaction belong to the oxidoreductase class.