Fluid mosaic model : A model that describes the structure of cell membranes . This model conceived by S.J.Singer and G.L.Nicolson in 1972 to describe the structural features of biological membrane . In this model a flexible layer made of lipid molecules is interspersed with large protein molecules that act as channels through which other molecules enter and leave the cell.
The plasma membrane of cells has two layers (a bilayer) of phospholipids. Each phospholipids molecules has a polar head and nonpolar tail. In lipid bilayer the non polar regions of the phospholipids in each layer face the core of the bilayer ,because nonpolar tail is hydrophobic and their polar head (hydrophilic) groups face outward interacting with the aqeous phase on either side.
Figure : Fluid Mosaic Model of cell Membrane
Proteins are embedded in this bilayer sheet held by hydrophobic interactions between the membrane lipids and hydrophobic domains exposed on both sides, giving the membrane the look of a mosaic .The fatty acyl chains in the interrior of the membrane form a fluid hydrophobic region and integral proteins float in this sea of lipid and the carbohydrate moieties attached to some proteins .
The membrane is assymmetric due to the irregular distribution of proteins .The lipid and protein units in membrane form an appearence of mosaic or a ceramic tile unlike a fixed mosaic of ceramic tile and mortar is free to change constantly. The membrane mosaic is fluid because most of the interactions among its components are noncovalent ,leaving individual lipid and protein molecules free to move literally in the plane of the membrane.
Very brief description of Fluid Mosaic Model of Plasma membrane explaining fluid nature of lipid bilayer with peripheral and integral proteins randomly distributed
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