Question

What are the five categories of proteins commonly found in plasma membranes and what is the function of each one?

Answer 1

The plasma membrane is also known as the cell membrane. It surrounds the cellular organelles and the cytoplasm of the cells. It also regulates the permeability and protects the cell from the outside environment.

Complete answer:
The most accepted and recent theory about the structure of the plasma membrane is the 'fluid mosaic model'. According to this model, the plasma membrane mostly consists of lipid and protein. The basic structure is composed of a lipid bilayer, while the proteins are embedded on them.
The membrane proteins can be categorized into five different classes. They are:
-Transport proteins
These proteins are involved in the moving of ions, molecules, and solutes across the cell membrane. Transport by protein is mainly of two types. Such as facilitated diffusion and active transport.
Example:- Glucose transporter 1
-Signaling proteins
Signaling proteins mainly regulate the signal transduction pathways. They transfer molecular signals from the outside environment to the interior of the cell.
Example:- G proteins
-Recognition proteins
There are certain proteins with attached carbohydrates that recognize membrane proteins of other cells. They are known as recognition proteins. They help in cell communication.
Example:- Glycoproteins
-Joining proteins
Proteins on adjacent cells bind with each other for interaction between cells. They are known as joining proteins.
-Enzymes
Enzymes are found in the plasma membrane as peripheral proteins. They mainly initiate enzymatic processes for the cell. They are specific.
Example:- ATPase

Note:
-Proteins are also classified as integral, lipid anchored, and peripheral based on their position.
-The protein-induced transport across the cell membrane can occur with or without the ATP molecules.
-Proteins are occupied in the cell membrane at around $50\%$ of the total volume.