TCA Cycle: Acetyl CoA Condensation — NEET Biology
✅ Asked in NEET 2023How many times does decarboxylation occur during each TCA cycle? (NEET 2023)
How many times does decarboxylation occur during each TCA cycle? (NEET 2023)
The number of time(s) decarboxylation of isocitrate occurs during single TCA cycle is (NEET 2022 phase 2)
Which statement is wrong for Krebs’ cycle? NEET 2017
Answer & NCERT explanation
Correct answer: D — Twice
In each TCA cycle, decarboxylation occurs twice: first when isocitrate is converted to α-ketoglutarate by isocitrate dehydrogenase, and second when α-ketoglutarate is converted to succinyl-CoA by α-ketoglutarate dehydrogenase complex. Both reactions release CO2 and reduce NAD+ to NADH.
Read more NCERT concept on the PYQ
The TCA cycle starts with the condensation of acetyl group with oxaloacetic acid (OAA) and water to yield citric acid. The reaction is catalysed by the enzyme citrate synthase and a molecule of CoA is released. Citrate is then isomerised to isocitrate. It is followed by two successive steps of decarboxylation, leading to the formation of α-ketoglutaric acid
NTA focuses on the two successive decarboxylation steps in the TCA cycle that convert isocitrate to α-ketoglutarate, releasing CO₂. Students often confuse which molecules are decarboxylated or forget that CoA is released in the first step (citrate synthase reaction), not during decarboxylation. Key point: citrate synthase catalyzes acetyl-CoA + OAA condensation (releasing CoA), followed by isomerization to isocitrate, then two sequential decarboxylations. Remember the order: citrate → isocitrate → α-ketoglutarate (with 2 CO₂ molecules released). This is repeatedly tested because decarboxylation steps are critical for understanding energy release and respiration.
What does NCERT say about TCA cycle starts with?
Has this concept appeared in NEET?
Which chapter is this from?
Through deep analysis of NEET and NTA, 88 of 90 questions from the NEET 2026 paper were matched straight from the MedicNEET Biology question bank.
88/90MedicNEET's Biology question bank is built from the same NCERT lines NTA picks repeatedly. Not random MCQs — questions crafted exactly like NTA crafts them.