Question

Q4. For each of the following scenarios describe what happens in normal cells and cells with the perturbation A. A cell that has no functional flippasesi 1 B. A membrane that contains only saturated fatty acids in glycerophospholipids and sphingolipids. C. Chymotrypsin with serine 195 mutated to tyrosine 5 D. Membranes in a mammalian cell that can't take up or synthesize cholesterol

Answer 1

A. Flippases are the enzymes which are responsible for the movement of phospholipids within the same leaflet of the membrane and from one to another. In the absence of this enzyme movement of phospholipids will not occur and there will be no change in the permeability of the membrane under different environmental conditions.

B. Saturated fatty acid molecules are those which can tightly pack with each other because they do not have double bond in them. They are straight chain molecules. The presence of these fatty acids will make the membrane phospholipids to pack tightly with each other thereby decreasing membrane permeability.

C. Serine is present in the active site of chymotrypsinogen. Chymotrypsin is the enzyme which is involved in digestive process. It is responsible for activating trypsinogen to trypsin. If serine is mutated to tyrosine, then activation of trypsin and therefore digestion of proteins will not take place.

D. Cholesterol is a big size planar molecule which helps in the reordering of lipid molecules present in plasma membrane. It helps in the generation of more number of unsaturated fatty acids under high temperature conditions and saturated fatty acids under low temperature condition. In the absence of this cholesterol, the composition of plasma membrane will not change and the permeability would be highly affected.

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