The structure of cell membrane can be described by the fluid-mosaic model. The essential feature of fluid-mosaic model (by Singer and Nicolson, 1972 ) is that cell membranes are considered to be quasifluid structures in which the lipids and proteins are in mosaic manner. The Singer-Nicolson model considered the lipid-protein association (mosaic) to be hydrophobic. The fluidity of the membrane is the result of this hydrophobic interaction, thus a cell membrane shows fluid behaviour.