NEET 2024 Botany Question 141 Solution

Oxidation of substrate in the TCA cycle is coupled with the reduction of electron acceptors ($NAD^+$ or $FAD$): - Isocitrate to $\alpha$-ketoglutarate: Dehydrogenation coupled with $NAD^+ \rightarrow NADH + H^+$. - $\alpha$-ketoglutarate to Succinyl-CoA: Dehydrogenation coupled with $NAD^+ \rightarrow NADH + H^+$. - Succinate to Fumarate: Dehydrogenation coupled with $FAD \rightarrow FADH_2$. - Malate to Oxaloacetate: Dehydrogenation coupled with $NAD^+ \rightarrow NADH + H^+$.

During the conversion of succinyl-CoA to succinic acid, a molecule of GTP is synthesized by substrate-level phosphorylation: $$\text{Succinyl-CoA} + \text{GDP} + P_i \rightarrow \text{Succinate} + \text{GTP} + \text{CoA-SH}$$ This is a cleavage/hydrolysis of a high-energy thioester bond; it does not involve oxidation or reduction.

Conversion of succinyl-CoA to succinic acid does not involve oxidation of the substrate.