Beta-oxidation of an odd-chain fatty acid yields several acetyl-CoA molecules plus one molecule of propionyl-CoA as the final three-carbon fragment. For propionyl-CoA to enter the TCA cycle, it must first be converted to:
- A Acetoacetyl-CoA
- B Succinyl-CoA ✓
- C Pyruvate
- D Malonyl-CoA
Correct answer: B. Succinyl-CoA
Explanation
Propionyl-CoA is carboxylated by propionyl-CoA carboxylase (biotin-dependent) to D-methylmalonyl-CoA, racemized to the L-isomer, then rearranged by methylmalonyl-CoA mutase, a vitamin B12-dependent enzyme, to succinyl-CoA, a true TCA intermediate. This makes odd-chain fatty acids glucogenic, unlike even-chain fatty acids whose acetyl-CoA units cannot yield net glucose. Pyruvate is not formed at any point in this pathway, and acetoacetyl-CoA belongs to ketone body metabolism.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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