Question

The formation of Acetyl Co-A from pyruvic acid is the result of its
A. Reduction
B. Dehydration
C. Phosphorylation
D. Oxidative decarboxylation

Answer 1

Hint: Pyruvate is the end product of glycolysis. It is a three-carbon compound and releases carbon dioxide to form a two-carbon compound acetyl CoA.

Complete answer: The pyruvate is a three-carbon compound. It releases one molecule of carbon dioxide and forms a two-carbon compound called acetyl CoA.
This release of $CO_2$ is known as decarboxylation. This biochemical reaction is catalyzed by pyruvate dehydrogenase complex enzymes.
1. TPP or Thymine pyrophosphate, FAD, or Flavin adenine dinucleotide and lipoate are very much essential for this reaction as these substances help in the oxidation of pyruvate to acetyl CoA. It is an irreversible reaction.
2. In this reaction, NAD+ is oxidized to NADH.
3. The pyruvate dehydrogenase enzyme includes three enzymes as follows:
Dihydrolipoyl transacetylase,
Dihydrolipoyl dehydrogenase,
Pyruvate dehydrogenase or pyruvate decarboxylase.
4. This reaction takes place in mitochondria.
5. This reaction on;y initiates when aerobic respiration of glucose takes place. It is the only reaction that links glycolysis and the Krebs cycle.

So, the correct answer is option D. Oxidative decarboxylation.

Note: In the oxidative decarboxylation reaction, the oxidation process includes the removal of the carboxyl group from pyruvate as a molecule of $CO_2$ and decarboxylation refers to the pass out of $CO_2$ from the cell. The two remaining carbons form the acetyl group of Acetyl-CoA which reacts with oxaloacetate to form citric acid in the TCA cycle or Krebs cycle.