Botany · Respiration in Plants

NEET (UG) 2024 — Question 135

Identify the step in the tricarboxylic acid cycle which does not involve oxidation of substrate.

Option A:
Malic acid $\rightarrow$ Oxaloacetic acid
Option B:
Succinic acid $\rightarrow$ Fumaric acid $\rightarrow$ Malic acid
Option C:
Succinyl-CoA $\rightarrow$ Succinic acid
Correct
Option D:
Isocitrate $\rightarrow \alpha$ -ketoglutaric acid

Answer: C

Step-by-step solution

Oxidation in the TCA cycle is recognised by loss of hydrogen/electrons, usually to $\ce{NAD+}$ or $\ce{FAD}$ . $\ce{Malate -> Oxaloacetate}$ is an oxidation by $\ce{NAD+}$ . $\ce{Succinate -> Fumarate -> Malate}$ involves oxidation of succinate by $\ce{FAD}$ . $\ce{Isocitrate -> \alpha-Ketoglutaric\ acid}$ is an oxidative decarboxylation. $\ce{Succinyl-CoA -> Succinic\ acid}$ is a substrate-level phosphorylation and does not involve oxidation. Thus the step without oxidation of substrate is option C.

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Exam: NEET (UG) 2024
Paper: 2024 paper
Subject: Botany
Chapter: Respiration in Plants
Topic: Tricarboxylic Cycle

Match List-I with List-II. List I List II --- --- --- --- A. Citric acid cycle I. Cytoplasm B. Glycolysis II. Mitochondrial matrix C.…

Answer: C

Step-by-step solution

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