Biomembranes Summary Biological membranes are composed of proteins and lipids, with a small amount of carbohydrate. Noncovalent bonds hold the components of these lipid-protein assemblies together.
Membranes are highly asymmetric structures whose two leaflets have very different properties.
You should know that double bonds of fatty acids almost always have a cis configuration. Sphingolipids include sphingomyelins, cerebrosides and gangliosides. Cholesterol is based on a 4-ring structure that contains a hydroxyl group at one end and a short hydrocarbon tail at the other end. Its OH group lies close to the phosphate group of the polar head group of phospholipid molecules and the four rigid steroid rings interact with, and partly immobilize the regions of the hydrocarbon chains that are closest to the phospholipid head groups. Glycerophospholipids and sphingolipids form bilayers in which their nonpolar tails associate with each other and their head groups are exposed to the aqueous environment.