Krebs Cycle & Acetyl CoA Entry — NEET Biology
✅ Asked in NEET 2016Common molecule for breakdown of fats, carbohydrates, and proteins is: NEET 2016
Common molecule for breakdown of fats, carbohydrates, and proteins is: NEET 2016
Answer & NCERT explanation
Correct answer: D — Acetyl-CoA
Acetyl-CoA is the common molecule where breakdown pathways of fats (β-oxidation), carbohydrates (glycolysis), and proteins (deamination) converge. All three macromolecules are eventually converted to acetyl-CoA, which then enters the TCA cycle for complete oxidation. It's the universal fuel molecule for cellular respiration.
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The acetyl CoA then enters a cyclic pathway, tricarboxylic acid cycle, more commonly called as Krebs' cycle after the scientist Hans Krebs who first elucidated it.
The Krebs cycle (TCA cycle) is a cyclic pathway where acetyl CoA enters and undergoes oxidation to produce NADH, FADH2, and GTP/ATP. Students often confuse where acetyl CoA is formed (from pyruvate via pyruvate dehydrogenase complex) with where it enters the cycle (combines with oxaloacetate to form citrate). The trap is forgetting that this is a cyclic process—oxaloacetate is regenerated at the end, making it a catalyst. Remember: one acetyl CoA (2 carbons) enters per turn, two CO2 are released, and the cycle occurs twice per glucose molecule in the matrix of mitochondria.
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