4 Which of the following lipid bilayers would have the great

4. Which of the following lipid bilayers would have the greatest fluidity and permaeability (at room temperature)?

a) A bilayer constructed of saturated phospholipids and fewer cholesterol molecules.

b) A bilayer constructed of unsaturated phospholipids and more cholesterol molecules.

c) A bilayer constructed of saturated phospholipids and more receptor proteins.

d) A bilayer constructed of unsaturated phospholipids and less cholesterol molecules.

e) A bilayer constucted of unsaturated phospholipids, more cholesterol molecules, and more receptor proteins.

Solution

D is the answer.

Cholesterol increases membrane packing to reduce membrane fluidity and permeability.

The fatty acid tails of phospholipids also affect membrane fluidity. fatty acids with no double bonds in the hydrocarbon that is saturated fatty acids make membranes more rigid and stronger.

Cis- unsaturated fatty acids increase membrane fluidity and permeability.

One easiera way to identify the effect on fluidity is that lipids that can pack more tightly make membranes more rigid and stronger but less fluid.