Arachidonic acid is the specific precursor for all prostaglandins. This multiple-choice question tests a key concept in biochemistry relevant to exams like GATE Life Sciences.

Question Breakdown

The query asks for the specific precursor for all prostaglandins from these options: (A) Oleic acid, (B) Arachidonic acid, (C) Palmitic acid, (D) α-Linolenic acid.

Option Analysis

• (A) Oleic acid: This is a monounsaturated omega-9 fatty acid (C18:1). It influences prostaglandin ratios (e.g., PGE2:PGF2α) in specific contexts like cell cultures but is not the direct precursor for prostaglandin synthesis.

• (B) Arachidonic acid: This polyunsaturated omega-6 fatty acid (C20:4) is the direct and specific precursor. It is released from membrane phospholipids by phospholipase A2 and converted via cyclooxygenase (COX) enzymes into PGH2, the common intermediate for all prostaglandins (PGE2, PGF2α, PGI2, etc.).

• (C) Palmitic acid: A saturated fatty acid (C16:0), it serves as a general energy source and membrane component but plays no role in prostaglandin biosynthesis.​

• (D) α-Linolenic acid: An essential omega-3 polyunsaturated fatty acid (C18:3), it leads to other eicosanoids but not prostaglandins, which derive exclusively from arachidonic acid.​

Correct Answer: (B) Arachidonic acid. Prostaglandins belong to the eicosanoid family, and their unified pathway starts from arachidonic acid.​

Introduction
In biochemistry, understanding the specific precursor for all prostaglandins is crucial for competitive exams like GATE Life Sciences. Prostaglandins regulate inflammation, pain, and fever, and their synthesis hinges on one key fatty acid: arachidonic acid. This article breaks down the options—oleic acid, arachidonic acid, palmitic acid, and α-linolenic acid—to clarify the correct answer and pathway.

Prostaglandin Biosynthesis Pathway

Prostaglandins form via the cyclooxygenase pathway:

1. Arachidonic acid (20:4 n-6) is liberated from phospholipids.

2. COX-1/COX-2 convert it to PGH2.

3. PGH2 yields specific prostaglandins (PGE2, PGD2, etc.).
   No other listed fatty acid directly feeds this pathway.

Why Not the Other Options?

Exam Relevance

For GATE Life Sciences, memorize arachidonic acid as the specific precursor for all prostaglandins. Linoleic acid (not listed) converts to arachidonic acid upstream, but it’s not direct. Inhibitors like aspirin target COX to block this.