The main molecules present in the plasma membrane are phospholipids, those molecules are made of a polar, hydrophil end(glycerol with a phosphate group attached) and two non-polar, hydrophobe ends(two fatty acids rests). The cell identity is determined by proteins present in the membrane, a very important type of protein that determines the identity of a specific cell is called marker. The membrane fluidity is reduced by a lipid with a ring structure, cholesterol, this molecule belongs to a class of biomolecules called steroids.
