Question

In which of the following steps of citric acid cycle, $C{O}_2$ is evolved?
$\begin{array}{ccc}I.Citricacid& \to & \alpha -ketoglutaricacid\\ II.Succinicacid& \to & Malicacid\\ III.Malicacid& \to & Oxaloaceticacid\\ IV.\alpha -ketoglutaricacid& \to & SuccinylCo-A\end{array}$
Select the correct answer using the codes given below

• A. I and II
• B. I and IV
• C. II and III
• D. II and IV
• E. III and IV

Answer 1

The correct option is B I and IV

Citric acid cycle or Krebs, cycle is the process where pyruvate (reduced from glycolysis) is broken down into $C{O}_2$ and water. It takes place in the mitochondrial matrix of the cell. During citric acid cycle, the steps where $C{O}_2$ is evolved are:
(i) During the formation of $\alpha$-ketoglutaric acid (5C) from citric acid (6C) with the formation of $NADH+H^{+}$ from $NA{D}^{+}$.

(ii) During the formation of succinyl Co-A (4C) from $\alpha$-ketoglutaric acid (5C) with the formation of $NADH+H^{+}$.