Acetyl-CoA generated inside mitochondria cannot cross the inner membrane directly. In the fed state, how does mitochondrial acetyl-CoA reach the cytosol for fatty acid synthesis?

• A As free acetate transported by monocarboxylate carriers
• B Condensed with oxaloacetate to form citrate, which exits via the tricarboxylate transporter ✓
• C Converted to acetylcarnitine by carnitine acetyltransferase
• D Reduced to ethanol and diffused across the membrane

Explanation

Mitochondrial acetyl-CoA condenses with oxaloacetate to form citrate, which crosses the inner membrane on the tricarboxylate carrier. Cytosolic ATP-citrate lyase then cleaves citrate back to acetyl-CoA and oxaloacetate. Acetylcarnitine is a minor route used mainly by heart and skeletal muscle, not the principal hepatic pathway, so option C is the tempting distractor that fails.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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