In this article we will discuss about the structure of plasma membrane. This will also help you to draw the structure and diagram of plasma membrane.
1. The membrane which bounds the protoplasm (Fig. 292) of the cell of all living organisms including plants and animals is known as plasma membrane or cell membrane or plasmalemma.
2. Plasma membranes range from 7.5 nm to 10 nm in thickness.
3. These are composed of approximately 60% protein and 40% phosphoglyceride.
4. According to Davson and Danielli (1935) plasma membranes are made up of a central region consisting of phosphoglycerides and an outer denser region composed of proteins.
5. The phosphoglyceride molecules are believed to be arranged in two rows with their hydrophilic polar heads towards the outer edges and their hydrophobic hydrocarbon tails in the centre.
6. Plasma membranes are selectively permeable controlling the passage of materials into and out of the cells.
7. The proteins of the membrane include enzymes and compounds of the active transport system.
8. The membrane is relatively impermeable to charged ions, which enter the cell by means of active transport system.
9. The main lipid compounds are lecithin, cephalin and cholesterol.
Functions of plasma membrane include:
(i) osmosis,
(ii) active transport,
(iii) phagocytosis, and
(iv) pinocytosis.