Chemical studies on the human RBCs showed that the cell membrane is composed of a lipid bilayer.
The lipids are arranged within the membrane with the outer polar head and the inner hydrophobic tails. This ensures that the non-polar tail of saturatedhydrocarbons is protected from the aqueous environment.
The lipid component of the membrane mainly consists of phosphoglycerides.
Cell membranes also possess protein and carbohydrate.
Ratio of protein and lipid varies in different cells. E.g. In human RBC, membrane has 52% protein and 40% lipids.
Depending on the ease of extraction, membrane proteins are 2 types:
o Integral proteins: Partially or totally buried in membrane.
o Peripheral proteins: Lie on the surface of membrane.
Fluid mosaic model of cell membrane: Proposed by Singer & Nicolson (1972). According to this, the quasi-fluid nature of lipid enables lateralmovement of proteins within the overall bilayer. This ability to move within the membrane is measured as its fluidity.
