Proteins: Structure And Functions

In junior classes, you must have learned that proteins are the building blocks of life. Well, you’ve learned it right and now we will explain how. Proteins are the most common cells found in all living organisms. They constitute the major part of a cell’s dry mass; more than lipids and carbohydrates combined.

What are Proteins?

Protein is a polymeric chain of amino acid residues. Amino acids link up to form polypeptide chains. One or several of such chains link up to form a protein. Amino acids are substituted methanes, where the four valencies of the α-C are occupied by hydrogen, an amino group, a carboxylic group and the fourth valency, is fulfilled by a variable R- group. Depending on the R- there are different types of amino acids, out of which 20 are found in a polypeptide chain. The structure of protein is classified at 4 levels:-

Protein Structure

Protein structure

  • Primary – The primary structure of a protein is the linear polypeptide chain formed by the amino acids in a particular sequence. Changing the position of even a single amino acids will result in a different chain and hence a different protein.
  • Secondary – The secondary structure of a protein is formed by hydrogen bonding in the polypeptide chain. These bonds cause the chain to fold and coil in two different conformations known as the α-helix or β-pleated sheets. The α-helix is like a single spiral and is formed by hydrogen bonding between every fourth amino acid. The β-pleated sheet is formed by hydrogen bonding between two or more adjacent polypeptide chains.
  • Tertiary – The tertiary structure is the final 3-dimensional shape acquired by the polypeptide chains under the attractive and repulsive forces of the different R-groups of each amino acid. This is a coiled structure that is very necessary for the protein functions.
  • Quaternary – This structure is exhibited only by those proteins which have multiple polypeptide chains combined to form a large complex. The individual chains are then called subunits.

Functions of Protein

Proteins play myriad functions in the body and cell. Some prominent functions are:-

  1. Movement – Myosin is a protein found in muscles which enables the contraction of muscles making movement possible.
  2. Structure and Support – Keratin is the structural protein which makes our hair, nails, and horns in animals.
  3. Digestion – Digestion is carried out by the digestive enzymes which are basically proteinaceous in nature.
  4. Cellular communication – Cells communicate with other cells and the external environment via receptors present on the surface of cells. These receptors are made of proteins.

Stay tuned with Byju’s to learn more about structure and functions of proteins.

Practise This Question

Find out the wrongly matched pair.