A vegan diet lacking animal fats leads to scaly dermatitis and poor wound healing. Humans cannot introduce double bonds beyond the delta-9 position of a fatty acid because they lack certain desaturases. Which fatty acid must therefore be obtained from the diet as the precursor of arachidonic acid?
- A Linoleic acid (18:2, delta-9,12) ✓
- B Palmitic acid (16:0)
- C Oleic acid (18:1, delta-9)
- D Erucic acid (22:1, delta-13)
Correct answer: A. Linoleic acid (18:2, delta-9,12)
Explanation
Humans possess delta-4, delta-5, and delta-6 desaturases but lack delta-12 and delta-15 desaturases, so double bonds beyond carbon 9 cannot be synthesized de novo. Linoleic acid (18:2 n-6) is the essential omega-6 fatty acid that is elongated and desaturated to arachidonic acid, the precursor of eicosanoids. Oleic acid can be made from saturated precursors via delta-9 desaturation, which kills option C.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.