Question 57:
Phosphatidylcholine and phosphatidylserine are examples of:
The correct answer is (C) Glycerophospholipids.
Phosphatidylcholine and phosphatidylserine are glycerophospholipids, characterized by a glycerol backbone esterified to two fatty acids and a phosphorylated head group (choline or serine, respectively).
Option Breakdown
(A) Fatty acids
Fatty acids are simple carboxylic acids with hydrocarbon chains (e.g., palmitic acid), serving as building blocks for complex lipids, not the amphipathic bilayer formers like phosphatidylcholine.
(B) Glycerolipids
This broad class includes triglycerides (glycerol + 3 fatty acids) and diglycerides, lacking the phosphate group that defines phosphatidylcholine and phosphatidylserine.
(C) Glycerophospholipids
Correct; both PC (lecithin) and PS feature glycerol-3-phosphate with variable fatty acyl chains at sn-1/sn-2 and polar heads, forming cell membrane bilayers.
(D) Sphingolipids
Sphingolipids use sphingosine backbone (e.g., sphingomyelin, cerebrosides), distinct from glycerol-based phospholipids like PC/PS.
Introduction to Phosphatidylcholine Phosphatidylserine Glycerophospholipids
Phosphatidylcholine phosphatidylserine glycerophospholipids classification identifies them as major membrane components with glycerol-phosphate backbone. Essential for GATE Life Sciences biochemistry lipid questions.
Structure of Glycerophospholipids
PC has choline head (quaternary ammonium), PS has serine (amino + carboxyl); both amphipathic with hydrophobic tails for bilayers. PS flips to inner leaflet, signaling apoptosis.
Synthesized via CDP-diacylglycerol pathway in ER.
Lipid Classes Comparison Table
| Option | Backbone | Phosphate? | Examples |
|---|---|---|---|
| Fatty acids | None | No | Palmitate, oleate |
| Glycerolipids | Glycerol | No | Triglycerides |
| Glycerophospholipids | Glycerol | Yes | PC, PS |
| Sphingolipids | Sphingosine | Some | Sphingomyelin |
Confirms phosphatidylcholine phosphatidylserine glycerophospholipids match.
Exam Relevance for Life Sciences
Connects to prior lipids (steroids, prostaglandins, fat-soluble vitamins); memorize “phospho” = phosphate for quick PYQ solving.
