The Two Monolayers of the Plasma Membrane in a Human

Question

The two monolayers of the plasma membrane in a human red blood cell …
A) have different overall electrical charges, with negatively charged phospholipids (e.g. phosphatidylserine) normally enriched in the inner monolayer.
B) have the same abundance of phosphatidylinositol.
C) exchange phospholipids only through spontaneous flip-flops.
D) both contain glycolipids.
E) both contain gangliosides.

Accepted Answer

While glycolipids such as gangliosides are limited to the outer monolayer, phosphatidylinositol and the negatively charged phosphatidylserine are mostly found in the inner monolayer. Membrane proteins actively maintain the asymmetry of the bilayer by regulated transport of the lipids between the monolayers.