Q.47 During cellular respiratory process, pyruvate must be oxidized to
acetyl CoA and
CO2 before it enters the citric acid cycle.
The corresponding simplified equation is:
Pyruvate + NAD+ + CoASH → Acetyl-S-CoA + NADH + CO2
This oxidation reaction occurs in mitochondria and is carried out in presence of the enzyme:
Introduction
During cellular respiration, pyruvate produced from glycolysis cannot directly
enter the citric acid cycle. It must first be oxidized to acetyl-CoA inside the
mitochondria. This step is known as the link reaction and is frequently tested in
competitive examinations such as CSIR-NET, GATE, JAM, and NEET.
Given Reaction
Pyruvate + NAD+ + CoA-SH → Acetyl-S-CoA + NADH + CO2
- Occurs in the mitochondria
- Involves oxidation and decarboxylation
- Produces NADH for the electron transport chain
Key Features of the Reaction
- Oxidation: NAD+ is reduced to NADH
- Decarboxylation: CO2 is released
- Acetyl group transfer: Acetyl group binds to CoA
Correct Answer
Option (B): Pyruvate dehydrogenase
Why Pyruvate Dehydrogenase Is Correct
Pyruvate dehydrogenase is a multi-enzyme complex located in the mitochondrial
matrix. It catalyzes the oxidative decarboxylation of pyruvate, resulting in the formation of
acetyl-CoA, NADH, and CO2. This reaction serves as the metabolic bridge between
glycolysis and the citric acid cycle.
Conclusion
The conversion of pyruvate to acetyl-CoA before entry into the citric acid cycle is catalyzed
by the pyruvate dehydrogenase complex. Recognizing this reaction is essential
for understanding cellular respiration and scoring well in competitive examinations.
