Correct Answer: 2. Arachidonic acid

Prostaglandins derive from arachidonic acid, a 20-carbon polyunsaturated fatty acid, via the cyclooxygenase pathway in most cells.

Option Analysis

1. Oleic acid
Oleic acid (C18:1, monounsaturated) is common in olive oil but lacks multiple double bonds needed for eicosanoid synthesis. Cannot serve as prostaglandin precursor.​

2. Arachidonic acid
C20:4 (ω-6), released from membrane phospholipids by phospholipase A2. COX-1/COX-2 convert it to PGH2, then specific synthases yield PGE2, PGI2, etc. Correct answer.

3. Cervonic acid
Cervonic acid (C24:1, very long-chain monounsaturated) occurs in brain sphingolipids. Wrong carbon count and unsaturation prevent prostaglandin formation.​

4. Linoleic acid
C18:2 (ω-6), essential fatty acid and arachidonic acid precursor via elongation/desaturation. Not directly used; requires conversion first.​

Prostaglandins synthesized from the 20-carbon polyunsaturated fatty acid arachidonic acid drive inflammation, pain, and homeostasis via COX pathways. This prostaglandins synthesized 20-carbon polyunsaturated fatty acid arachidonic acid breakdown aids med students and biochem exam prep like USMLE or GATE Life Sciences.

Biosynthesis Pathway

Arachidonic acid (AA) liberates from phospholipids → COX enzymes form PGG2/PGH2 → isomerases produce PGE2, PGD2, PGI2 (prostacyclin). Inhibited by aspirin/NSAIDs targeting COX.

Fatty Acid Comparison

Arachidonic acid’s four double bonds enable cyclization into prostaglandin rings.​

Physiological Roles

PGE2 mediates fever/pain; PGI2 prevents clotting; LTs from lipoxygenase path cause asthma. Exam tip: “Arachidonic = 20:4 for PGs; linoleic feeds it upstream.”​​