The properties of a lipid bilayer are determined by the stru

The properties of a lipid bilayer are determined by the structure of its lipid molecules. Predict the properties of the lipid bilayers that would result if the following were true:

1. Phospholipids had only one hydrocarbon chain instead of two.

2. All of the hydrocarbons were unsaturated.

3. There were excessive amounts of cholesterol.

Solution

a) Presence of two hydrocarbon chains in phospholipids makes the size of head and tail nearly equal and allows formation of bilayer. Presence of single hydrocarbon chain would impart the whole phospholipid molecule a cone shape structure which in turn would not allow the formation of bilyer. Rather, these cone shaped phospholipids would form micelle as the larger heads would make circle around the smaller tails.
b) Presence of all unsaturated hydrocarbon chain would not allow the tight packing of phospholipids and would cause the membrane to be more fluid i.e. it would lower down the melting point of membrane. Also, presence of kinks between the hydrocarbon chains would allow even larger molecules to pass through it.
c) Cholesterol serves to fill the gaps between the unsaturated hydrocarbon chains of phospholipids. So, presence of excessive amount of cholesterol in membrane would make it more rigid and stiff by reducing its flluidity as well as would make it less permeable.