Summary of Fluid Mosaic Model of Plasma Membrane by Singer and Nicolson 1972

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.

Properties:

• 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 37^oC

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
See the Difference between Peripheral vs Intrinsic 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

Reference:

• Singer SJ, Nicolson GL (Feb 1972). "The fluid mosaic model of the structure of cell membranes". Science 175 (4023): 720–31.