Structure of Bacteria | Part 4 | Plasma membrane 

Structures internal to the cell wall
Welcome to part-4 of structure of bacteria series. We have discussed about structures external to the cell wall. Now, let’s discuss about the structures internal to the cell wall.
The main structures that are present inside the cell wall are...
Plasma membrane
Mesosome
Cytoplasm
Ribosomes
Genetic material
Plasmid
Plasma membrane, also called as cytoplasmic membrane, is present just beneath the cell wall.
Several models were proposed, to explain the structure of plasma membrane. However, the most widely accepted theory is, “Fluid mosaic model”, which was proposed by Singer and Nicolson in 1972.
According to this model, the plasma membrane is formed by two layers of Phospholipids. These two layers are arranged opposite to each other with slight overlap. The plasma membrane is mainly composed of three components. Phospholipids, Protein, and Cholesterol.
The Phospholipid molecule is composed of a phosphate group. and a lipid. Phospholipid is an asymmetric molecule, with a polar. and non-polar ends.
The polar end of Phospholipid is hydrophilic, and the non polar end is hydrophobic.
The two phospholipid layers are arranged in such a way that the polar ends of phospholipids of each layer, are directly exposed to internal and external environments of the cell. The reason for this arrangement is the internal and external environments of the cell are aqueous solutions in many cases, and the polar end being hydrophilic, it always interacts with water. And the non polar ends are left free inside.
This is the reason why, in the non polar solvent this condition may get reversed, and as a result the membrane gets damaged.
The phospholipid bilayer is integrated with protein molecules distributed throughout the layer. Some proteins are bound to the external part of the layer. These are called as peripheral proteins. Some proteins are totally merged in to the bilayer and are called integral proteins.
The integral proteins are so strongly bound that they can only be separated when the membrane is destructed. The peripheral proteins are loosely attached that they can be relocated their position within the membrane.
The cholesterol molecules present in the membrane, provide stability to the bilayer. They help the bilayer not to get separated too much in different environment conditions. The main function of plasma membrane is to control the entry and exit of selective bio molecules from the cell. Also protects the cell from its external environment.