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

Cholesterol, although lipid-soluble, cross most membranes by means of receptor-mediated endocytosis or transporters is given below

Propose a mechanism for co-transport of cholesterol through a plasma membrane is given below .

Explanation:

1.Cholesterol is a lipid-soluble molecule.If this is the only characteristic of the molecule so there will be no problem crossing the phospholipid bilayer due to its lipid solubility.

2.Cholesterol must cross most membranes by means of receptor-mediated endocytosis because it is a macromolecule.

3.Cholesterol functions to immobilise the outer surface of the membrane, reducing fluidity. It makes the membrane less permeable to very small water-soluble molecules that would otherwise freely cross. It functions to separate phospholipid tails and so prevent crystallisation of the membrane.

4.Most cholesterol is transported in the blood as cholesteryl esters in the form of lipid-protein particles known as low-density lipoproteins (LDL) (Figure 13-43). When a cell needs cholesterol for membrane synthesis, it makes transmembrane receptor proteins for LDL and inserts them into its plasma membrane