Question

Why must cholesterol, although lipid-soluble, cross most membranes by means of receptor-mediated endocytosis or transporters? Propose a mechanism for co-transport of cholesterol through a plasma membrane.

Answer 1

A) Cholesterol, although lipid-soluble, cross most membranes by means of receptor-mediated endocytosis or transporters as it is a macromolecule, so transported by passive transport. Active transport occurs when the molecule is very big, or when cell consume large amounts of the substance at once.

Cholesterol is transported by two mechanisms:

- Cells can synthesis cholesterol from acetyl-CoA.

- Cholesterol is also transported from the external environment which is dietary cholesterol.

Cholesterol transported by means of receptor-mediated endocytosis or transporters because cholesterol pack into the fatty acid tails of a membrane that reduces membrane permeability.

Cholesterol transported in the plasma when bound to lipoprotein carriers that are too large to pass through the phospholipid bilayer.

B) Mechanism for co-transport of cholesterol through a plasma membrane is :

The coupled transport of sodium and cholesterol explains of cholesterol through a plasma membrane. Here, these two molecules are transported in the same direction, therefore called as symport transport.

Sodium ion uses the kinetic energy that is harnessed from the potential energy from action of the sodium potassium pump that drags a cholesterol molecule with it through a protein pump and enable it to crosses the plasma membrane ...