AP BIOLOGY

Detailed explanation-1: -The main role of cholesterol in cell membrane is to provide structure and support to the membrane. Cholesterol is situated in the cell membrane in between the phospholipids. The rigid rings of the cholesterol molecule interact with the hydrophobic tails of the phospholipids.

Detailed explanation-2: -The fatty acids of most natural phospholipids have one or more double bonds, which introduce kinks into the hydrocarbon chains and make them difficult to pack together. The long hydrocarbon chains of the fatty acids therefore move freely in the interior of the membrane, so the membrane itself is soft and flexible.

Detailed explanation-3: -Cholesterol is also a key determinant of membrane fluidity: at high temperatures, cholesterol acts to stabilize the cell membrane and increase its melting point; while at low temperatures, it inserts into phospholipids and prevents them from interfering with each other to avoid aggregation [39].

Detailed explanation-4: -Cholesterol makes the bilayer stronger, more flexible but less fluid, and less permeable to water-soluble substances such as ions and monosaccharides. The above illustration of a cell membrane was modified from Wikipedia.

Detailed explanation-5: -Comprising 30 mol % of the lipids in cell membranes, cholesterol plays vital biophysical roles in monolayer and bilayer membranes. It increases the lipid-packing density and maintains high membrane fluidity.