Question

Identify X, Y and Z in the given diagram of citric acid cycle and select the correct option.

• A. X-GTP, Y-$NAD{H}_2$, Z-$FAD{H}_2$
• B. X-$FAD{H}_2$, Y-$NAD{H}_2$, Z-GTP
• C. X-$NAD{H}_2$, Y-$FAD{H}_2$, Z-GTP
• D. X-$C{O}_2$, Y-$NAD{H}_2$, Z-ADP

Answer 1

Answer: (C)

X-$NAD{H}_2$, Y-$FAD{H}_2$, Z-GTP

The given diagram is of citric acid cycle. It is also called as Krebs cycle. When isocitric acid is converted to α-ketoglutaric acid, NAD${}^{+}$ is converted to NADH${}_2$ and CO${}_2$ is liberated. This reaction is carried out by enzyme isocitrate dehydrogenase. This α-ketoglutaric acid undergoes oxidative decarboxylation and succinyl CoA is generated with liberation of NADH${}_2$ and CO${}_2$. This reaction is carried out by enzyme α-Ketoglutarate dehydrogenase. Succinyl CoA undergoes phosphorylation to produce succinic acid. In this step, GTP is formed from GDP. Succinic acid then undergoes oxidation to produce Fumaric acid by enzyme succinate dehydrogenase. FADH${}_2$ is generated from FAD in this step.

Thus, the correct answer is 'X-NADH${}_2$, Y-FADH${}_2$, Z-GTP.'