Which fatty acid must be supplied in the diet because humans lack the enzymes to introduce double bonds beyond the delta-9 position, and serves as the precursor of arachidonic acid?

• A Oleic acid (18:1, delta-9)
• B Linoleic acid (18:2, delta-9,12) ✓
• C Arachidic acid (20:0)
• D Stearic acid (18:0)

Explanation

Human desaturases can only insert double bonds between an existing bond and the carboxyl end (delta-4 through delta-9). Linoleic acid has a double bond at delta-12, beyond this reach, making it essential. It is elongated and desaturated by delta-6 and delta-5 desaturases to arachidonic acid, the substrate for eicosanoid synthesis. Oleic acid is made endogenously by stearoyl-CoA desaturase, killing distractor A.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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