Identify the step in tricarboxylic acid cycle, which does not involve oxidation of substrate.
- Malic acid Oxaloacetic acid
- Succinic acid Malic acid
- Succinyl-CoA Succinic acid
- Isocitrate -ketoglutaric acid
Answer
(3) Succinyl-CoA Succinic acid
Solution
Malic acid oxaloacetic acid: dehydrogenation, NAD+ is reduced to NADH + H+ (oxidation).
Succinic acid malic acid (via fumaric acid): FAD is reduced to FADH2 (oxidation).
Isocitrate -ketoglutaric acid: oxidative decarboxylation, NADH is formed (oxidation).
Succinyl-CoA succinic acid: substrate-level phosphorylation forming GTP (ATP); no hydrogen is removed, so the substrate is not oxidised.
Answer: (3)