Q.6 Cephalin, a biological surfactant, is
(A) choline phosphoglyceride
(B) ethanolamine phosphoglyceride
(C) glycosphingolipid
(D) sphingolipid

Cephalin, a Biological Surfactant: MCQ Solution and Detailed Explanation

Cephalin functions as a biological surfactant due to its amphipathic structure, which includes a hydrophilic phosphate head and hydrophobic fatty acid tails, enabling it to reduce surface tension in cell membranes. The correct answer to the question is (B) ethanolamine phosphoglyceride.

Option Analysis

• (A) Choline phosphoglyceride: This refers to phosphatidylcholine, commonly known as lecithin, which contains choline as the head group attached to a glycerol backbone with two fatty acids and phosphate. Unlike cephalin, lecithin does not match the ethanolamine-based structure and is less associated with cephalin nomenclature.

• (B) Ethanolamine phosphoglyceride: This is phosphatidylethanolamine (PE), the defining component of cephalin, featuring ethanolamine linked to the phosphate group on a glycerophospholipid backbone. Cephalin’s surfactant properties arise from this structure, abundant in brain tissues and cell membranes.

• (C) Glycosphingolipid: These lipids contain a ceramide backbone with attached carbohydrate chains, lacking glycerol and phosphate-ethanolamine, and serve roles in cell recognition rather than primary surfactant function.

• (D) Sphingolipid: Broad class with sphingosine backbone instead of glycerol; includes sphingomyelin but excludes glycerophospholipids like cephalin, which relies on glycerol for its amphipathic surfactant activity.

Cephalin, a biological surfactant essential in life sciences, is ethanolamine phosphoglyceride, playing a key role in membrane fluidity and signaling. This phospholipid stands out in competitive exams like CSIR NET due to its distinction from similar lipids.

Chemical Structure

Cephalin features a glycerol backbone esterified with two fatty acids, a phosphate group, and ethanolamine, creating its amphiphilic nature for surfactant action. Unlike choline phosphoglyceride (lecithin), the ethanolamine head provides a zwitterionic property suited for brain tissues.

Biological Role

As a biological surfactant, cephalin stabilizes lipid bilayers, aids blood clotting via platelets, and supports membrane protein function. It comprises up to 25% of cellular phospholipids, vital in nervous tissue.

Exam Relevance

In CSIR NET questions on cephalin as a biological surfactant, ethanolamine phosphoglyceride is the precise match, eliminating sphingolipids and glycosphingolipids based on backbone differences. Glycosphingolipids involve sugars on ceramide, irrelevant here.