Question

Are the following lipid samples likely to correspond to the inner or outer leaflet of a eukaryotic plasma membrane? (a) 20% phosphatidylcholine, 15% phosphatidylserine, 65% other lipids. (b) 35% phosphatidylcholine, 15% gangliosides, 5% cholesterol, 45% other lipids.

Short answer

(a)The lipid sample having 20% phosphatidylcholine, 15% phosphatidylserine and 65% other lipids correspond to the inner leaflet of the eukaryotic plasma membrane.

(b) The lipid sample having 35% phosphatidylcholine, 15% gangliosides, and 45% other lipids corresponds to the outer leaflet of the eukaryotic plasma membrane.

Step-by-step solution

Eukaryotic Plasma Membrane

The plasma membrane refers to the cell membrane. The plasma membrane of eukaryotes is a lipid-based double-layer membrane. The cell membrane serves as a barrier between the inside and outside of the cell.

The primary phospholipids found in the plasma membrane are phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and sphingomyelin.

Explanation for (a)

The amounts of protein and lipid content on both sides of biological membranes are not equal. Phosphatidylethanolamine and phosphatidylserine make up the majority of the inner leaflet's composition. Thus, the lipid sample containing 20% phosphatidylcholine, 15% phosphatidylserine, and 65% other lipids refers to the inner leaflet of the plasma membrane.

Explanation for (b)

Phosphatidylcholine and sphingomyelin are majorly found in the outer leaflet of the cell membrane. Thus, the lipid sample containing 35% phosphatidylcholine, 15% gangliosides, 5% cholesterol, and 45% other lipids refers to the outer leaflet of the plasma membrane.