Question

Is the composition of lipids in biological membrane identical on both leaflets? If not mention what the asymmetries are and how can they arise? *

Answer 1

Plasma membrane the outermost covering of all the living cell. It is made up of phospholipids and proteins.

Plasma membrane in all the living cell is made up of two layers, outer and inner leaflet and this is the reason we say that plasma membrane is a bilayer. Both the leaflets are equally populated with the number of phospholipids. But the type of phospholipids is different in each leaflet.

The composition is as follows -

Outer leaflet - phosphatidylcholine and sphingomyelin

Inner leaflet - phosphatidylethanolamine and phosphatidylserine

Because of the differential composition of the two leaflets of plasma membrane the plasma membrane it take to be asymmetric in nature.

This asymmetric distribution of phospholipids in the plasma membrane arises due to the action of cholesterol. It is a big size planar molecule which helps in lipid reordering.

Apart from cholesterol, enzymes called as flippases and floppases are responsible for the movement of phospholipids from one leaflet to the other and ensures that both the leaflets are equally populated with phospholipids and both of them contain different types of phospholipids.

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