Question

1) Define the membrane fluidity and the transition temperature of a biological membrane. List some of the factors that can affect membrane fluidity? Explain.

2) How does cholesterol regulate membrane fluidity over a wide range of physiological temperatures? Explain.

3) Give one example about how cholesterol plays a role in:

-cell signaling / signal reception
-intracellular transport

Answer 1

1. Biological membrane are usually made by lipid bilayer and the viscosity present in them is defined as the membrane fluidity.

The temperature at which the lipid bilayer undergoes one physical state to the other state (i. e) solid gel form to liquid state is known as the transition temperature of the biological membrane and it usually varies depending on the head group, charge and hydrocarbon length.There are many factors that affect the membrane fluidity the major are temperature, cholesterol and presence of unsaturated fatty acids.

2. Cholesterol is usually present between the lipid bilayer and has the important function (i. e) maintaining membrane fluidity at varying temperature. During high temperature it makes the melting temperature high and thus decrease the fluidity. Whereas in low temperature it intrude with the phospholipid and prevent clustering and increases the fluidity.

3. Cholesterol act as a ligand biogenesis in the hedgehog pathway in which the ligand are modified by them. They also act as a signal transduction. Intracellular transport of cholesterol is important to maintain its balance level within the cell. Usually the cholesterol is synthesised in endoplasmic reticulum and sent to golgi apparatus and it is transported via vesicles to plasma membrane.