Discussion 1:
1. Why must cholesterol, although lipid-soluble, cross most membranes by means of receptor-mediated endocytosis or transporters?
2. PROPOSE a mechanism for co-transport of CHOLESTEROL through a plasma membrane.
1. Cholesterol is a lipid-soluble molecule. If this is the only characteristic of the molecule that we consider about cholesterol, then it makes sense that it will have no problem crossing the phospholipid bilayer due to its lipid solubility. However, there are other factors that determine the ease with which molecules, ions, cross the membrane.
Cholesterol must cross most membranes by means of a receptor-mediated endocytosis because it is a macromolecule. This means of active transportation is usually employed when the molecule is too big, or the cell needs to consume large amounts of the substance at once.
2. This is my proposal but it is too simplistic and just uses what I know about the sodium-glucose co transport mechanism.
A mechanism for co-transport of sodium through a plasma membrane might be one of a symporter action couple with sodium ions. In this example, a sodium ion uses the kinetic energy harnessed from the potential energy derived from the primary action of the sodium potassium pump drags a cholesterol molecule with it through a protein pump and crosses the plasma membrane (this is how it works with glucose in the secondary active transport (symport)
I need to PROPOSE a similar example with cholesterol but it should be feasible and make sense. I am having problems coming up with a scenario similar to one in which the actions are similar to that of sodium and glucose