Mammalian tissues lack desaturases beyond the delta-9 position. Which fatty acid therefore cannot be synthesized de novo and must be obtained from the diet?
- A Palmitoleic acid (16:1, delta-9)
- B Linoleic acid (18:2, delta-9,12) ✓
- C Oleic acid (18:1, delta-9)
- D Stearic acid (18:0)
Correct answer: B. Linoleic acid (18:2, delta-9,12)
Explanation
Humans can introduce double bonds only at positions up to delta-9 from the carboxyl end. Oleic and palmitoleic acids are made by delta-9 desaturase from saturated precursors, so they are nonessential. Linoleic acid has a double bond at delta-12 that mammalian enzymes cannot create, making it an essential dietary fatty acid required for arachidonic acid and eicosanoid synthesis. Stearic acid needs no double bond at all.
Reference: Lehninger Principles of Biochemistry, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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