Q-114. Cholesterol present in LDL:
a) Represents primarily cholesterol that is being removed from peripheral cells.
b) Binds to a receptor and diffuses across the cell membrane.
c) On accumulation in the cell inhibits replenishment of LDL receptors.
d) When enters a cell, suppresses activity of acyl-CoA: cholesterol acyl-transferase (ACAT).
Answer: On accumulation in the cell inhibits replenishment of LDL receptors.
Explanation:
The mechanism of suppression of cholesterol biosynthesis by LDL-bound cholesterol involves specific LDL receptors that project from the surface of human cells.
The first step of the regulatory mechanism involves the binding of the lipoprotein LDL to these LDL receptors, thereby extracting the LDL particles from the blood.
Accumulation of intracellular cholesterol eventually inhibits the replenishment of LDL receptors on the cell surface, a phenomenon called down regulation, thereby blocking further uptake and accumulation of cholesterol.