Fluid mosaic model:
1. Fluid mosaic model was proposed by Singer and Nicholson (1972).
2. This model states that plasma membrane is made up of phospholipid bilayer and proteins.
3. Proteins are embedded in the lipid membrane like icebergs in the sea of lipids.
4. Phospholipid bilayer is fluid in nature.
5. Quasi-fluid nature of lipid enables lateral movement of proteins. This ability to move within the membrane is measured as fluidity.
6. Based on organization of membrane proteins they are of two types, as:
a. The intrinsic proteins occur at different depths of bilayer i.e. they are tightly bound to the phospholipid bilayer and are embedded in it. They span the entire thickness of the membrane. Therefore, they are known as transmembrane proteins. They form channels for passage of water.
b. The extrinsic or peripheral proteins are found on two surfaces of the membrane i.e. are loosely held to the phospholipid layer and can be easily removed.
