Question

Describe the fluid mosaic model of plasma membrane.

Answer 1

Plasma membrane:

1. Overton (1902) was the first man who studied the structure of plasma membrane and stated that it is composed of a thin layer of lipid.
2. Gorter and Grandell (1935) suggested that plasma membrane is made up of a double layer of lipid molecules.
3. Robertson (1961) gave a “unit membrane concept”. According to which all the membranes of the cell were constructed of protein-lipid-protein.
4. S.J. Singer and G. L. Nicolson in 1972 proposed “Fluid Mosaic Model” of the plasma membrane. According to this model, the quasi-fluid nature of lipids enables the lateral movement of proteins within the overall bilayer.

Fluid Mosaic Model: This model explains the structure of the plasma membrane of animal cells as a mosaic of components such as phospholipids, proteins, cholesterol, and carbohydrates. These components give a fluid character to the membranes. Components of plasma membranes are

1. Phospholipids – Phospholipids are the main fabric of the plasma membrane. They are amphipathic molecules with a hydrophilic head and a hydrophobic tail and attached to a glycerol molecule by a covalent bond.
2. Cholesterol – It is located between the phospholipids and phospholipid bilayers. It helps the plasma membrane to retain fluidity and prevents the compaction of hydrophilic tails at low temperatures and their expansion at high temperatures.
3. Proteins – The plasma membrane has three types of proteins-
4. Integral Proteins: These proteins form channels to allow the movement of large molecules and ions across the hydrophobic layer of the membrane.
5. Peripheral Proteins: These are found embedded in a single leaflet of the membrane. They carry signals from one segment of the membrane and relay them to another.
6. Glycoproteins: They stabilize the membrane and are responsible for intercellular communication.
7. Carbohydrates – These are attached to proteins on the outside membrane layer.