Q.105 Regions of higher abundance of cholesterol molecules on the plasma membrane will
(A) be more fluid
(B) result in clogged arteries as it can detach from the plasma membrane
(C) be more rigid than the surrounding membrane
(D) have higher rates of lateral movement of proteins into and out of plasma membrane

Cholesterol-Rich Membrane Regions: Rigidity Explained

Cholesterol modulates plasma membrane properties by interacting with phospholipids. Higher cholesterol regions become more rigid due to its ordering effect on lipid tails.

Correct Answer

Option (C): Be more rigid than the surrounding membrane.
Cholesterol’s rigid steroid ring packs tightly between phospholipids, restricting acyl chain movement and reducing fluidity in fluid membranes, making those regions more rigid.

Option Breakdown

Option (A): More Fluid

Cholesterol decreases fluidity in unsaturated lipid-rich membranes by filling gaps and straightening chains, not increasing it. It only boosts fluidity in gel-phase saturated lipids, but plasma membranes are typically fluid.

Option (B): Clogged Arteries

Cholesterol stays embedded in membranes via its hydrophobic tail and hydrophilic head; it doesn’t detach to cause arterial clogs. Atherosclerosis involves blood LDL cholesterol deposition, unrelated to membrane shedding.

Option (C): More Rigid

In liquid-disordered phases, cholesterol induces liquid-ordered phases with higher order, thicker bilayers, and reduced dynamics, increasing rigidity compared to surrounding areas.

Option (D): Higher Protein Movement

Cholesterol-rich regions form ordered domains (lipid rafts) that slow lateral diffusion of proteins and lipids due to increased viscosity, not accelerate it.