Question

Who discovered the fluid mosaic model of plasma membrane?

Answer 1

The fluid mosaic model was first proposed in 1972 by researchers of the University of California, San Diego. It was used to describe the plasma membrane as the fluid combination of phospholipids, cholesterol, and proteins.

Complete step by step answer:
In 1972, a fluid mosaic model was proposed by Seymour Jonathan Singer and Garth L. Nicolson of the University of California, San Diego. It was used to describe the plasma membrane as a fluid combination of phospholipids, cholesterol, and proteins.

It states that plasma membrane is a bilayer of phospholipid molecules (it forms a bilayer and act as a barrier to most water-soluble substance) that moves within their monolayer through diffusion (it is the movement of molecules from a region of higher concentration to the region of lower concentration in presence of a concentration gradient.)

The Phospholipid tail is directed inwards and results in the formation of a hydrophobic environment whereas the head of the phospholipid faces towards the aqueous medium that surrounds the plasma membrane which indicates that it is hydrophilic.

Phospholipids may be saturated or unsaturated. The fluidity of a membrane depends upon the extent of unsaturation of phospholipids. The more the unsaturation, the more will be the fluidity.

There are three types of proteins. They are,
- Transport proteins which provide hydrophilic channels or passageways for ions and polar molecules to pass through the membrane
- Enzymes which results in hydrolysis of certain molecules. For example, disaccharides.
- Protein in the membrane of cells that are involved in the process of respiration and photosynthesis.

Some of the protein molecules are embedded in the outer layer, some in the inner layer, and some span the whole membrane.
Many lipids and proteins possess short branched carbohydrate chains that are attached to the surface and this results in the formation of glycolipids and glycoproteins. These glycolipids and glycoproteins form hydrogen bonds with water molecules which help to maintain the structure of the plasma membrane. In addition to that, they act as a receptor molecule and bind to hormones and neurotransmitters.

The cholesterol that is present possesses the hydrophilic head and hydrophobic tail. It regulates the fluidity of membrane which prevents the membrane from being too fluid or too rigid and hence, it provides mechanical stability.

Note: The fluid mosaic model describes the arrangement of membrane proteins as a mosaic of discontinuous particles that penetrate the lipid sheet. In addition to that, it also describes the plasma membrane as a dynamic structure whose components are mobile and are capable of interactions. Various modifications were made to the original fluid mosaic model which was proposed in 1972.