what is plasma membrane in detail, what is history of plasma membrane and functions of plasma membrane

The plasma membrane, also known as the cell membrane, is a biological membrane that separates the interior of all cells from the outside environment. It is composed of a lipid bilayer with embedded proteins that may constitute close to 50% of membrane content.

The lipid bilayer is semi-permeable, allowing only certain molecules to diffuse across the membrane. The proteins are involved in various functions such as transport of molecules and ions across the membrane, cell adhesion, cell signaling, and serve as enzymes.

The history of the plasma membrane theory dates back to the 19th century. In 1895, Charles Overton proposed that membranes were made of lipids. Later in 1925, E. Gorter and F. Grendel proposed the lipid bilayer hypothesis based on their studies on red blood cells. However, the current model of the plasma membrane, known as the fluid mosaic model, was proposed by S.J. Singer and G.L. Nicolson in 1972. This model suggests that the membrane is a fluid structure with proteins embedded in or associated with the lipid bilayer.

The functions of the plasma membrane include:

1. Protective barrier: It protects the cell from its external environment.

2. Regulation of transport: It regulates the movement of substances in and out of the cell, maintaining the balance of ions, nutrients, and water.

3. Cell signaling: It receives signals from the environment and other cells, and transmits them into the cell.

4. Cell adhesion: It helps cells to stick together and form tissues.

5. Energy transduction: It helps in the generation and use of chemical energy.