Proteins: Structure And Functions

Proteins

What are Proteins?

Proteins are known as the building blocks of life because they are the most abundant molecules present in the body and forms about 60% of the dry weight of cells. They are the most common cells found in all living organisms. Apart from cells, most of the enzymes, regulatory and structural parts of the body are made up of proteins. As a result, they are essential for the growth and development of an individual.

Food like eggs, pulses, milk and other milk products form the major high protein foods for the body.

Also read:  Proteins 

Protein Structure

Proteins are a polymeric chain of amino acid residues. The structure of a protein is mainly composed of long chains of amino acids. The structure and position of amino acids give particular properties to the proteins. Amino acids are made up of an amino functional group (-NH2) and a carboxyl group (-COOH).

 Amino Acids

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- carbon are occupied by hydrogen, amino group, carboxyl group, and the fourth valency is fulfilled by a variable R- group.

Depending on the R-group, there are different types of amino acids, out of which 20 are found in a polypeptide chain. All these properties of amino acids decide the ultimate structure and function of proteins.

The structure of the protein is classified at 4 levels:-

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 acid 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 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 multiple functions in the body and its structure gives it its functionality. Some prominent functions are:-

  1. Digestion – Digestion is carried out by the digestive enzymes which are basically proteinaceous in nature.
  2. Movement – Myosin is a protein found in muscles which enables the contraction of muscles making movement possible.
  3. Structure and Support – Keratin is the structural protein which makes our hair, nails, and horns in animals.
  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.
  5. Act as a messenger – These proteins function as the chemical messengers, which help in the communication between the cells, tissues, and organs.

Also refer: Biomolecules

Learn more about Proteins, its types, sources, importance and other related topics @ BYJU’S Biology

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