In mammalian fatty acid synthase, all catalytic activities reside on a single multifunctional polypeptide dimer except one component, which acts as the flexible arm carrying the growing acyl chain between active sites. This component is:

• A Acyl carrier protein ✓
• B Beta-ketoacyl reductase
• C Enoyl-CoA hydratase
• D Thioesterase

Explanation

Acyl carrier protein (ACP), bearing a phosphopantetheine prosthetic group derived from pantothenic acid (vitamin B5), swings the growing fatty acyl chain between the seven catalytic domains of the FAS dimer. Thioesterase releases the finished chain but does not carry intermediates. The phosphopantetheine arm is the same motif found in CoA, which explains why B5 deficiency impairs lipid metabolism broadly.

Reference: Lippincott's Illustrated Reviews: Biochemistry, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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