Proposed by S J Singer and Garth L Nicolson
Published in the journal “Science’’ in 1972.
Composition: Cell membrane is made up of lipid, protein and small amount of carbohydrate.
• Membrane is quasi fluid with components held together mostly by non-covalent interaction
• The fluidity of the membrane is α chain length and unsaturation of fatty acids
• The more the un-saturation (no. of double bonds), the more the fluidity of the membrane
• Increased fatty acid chain length decreases fluidity.
• Increased amount of cholesterol decreases fluidity at 37oC
1. Phospholipid bilayer
• Consists of polar hydrophilic (water loving) phosphate head group
• Non polar hydrophobic fatty acid chain
• Forms the structural backbone of the membrane that serves as a barrier to regulate the passage of substances
• Cholesterol bound with phospholipids makes membrane stable and highly impermeable to polar molecules
2. Proteins mostly globular
• A) Extrinsic or peripheral proteins are loosely attached to the lipid bi layer and are hydrophilic
• B) Intrinsic, integral or transmembarne proteins may serve as transport channels (permeases, translocases), receptor molecules, antigens etc. It forms about 70% of total membrane proteins
3. Carbohydrates are present on the outer side or extracellular side of the plasma membrane
• Present as glycoprotein or glycoli
• pid (carbohydrates bound to protein or lipid)
• Function : helps in cell recognition, cell interaction and cell adhesion
• As receptors, antigens etc
- Singer SJ, Nicolson GL (Feb 1972). "The fluid mosaic model of the structure of cell membranes". Science 175 (4023): 720–31.