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.

 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
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

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