Define Protein structure:
Protein structure is defined as a polymer of amino acids joined by peptide bonds. Let us see how a peptide bond is established from the following reaction:
We can thus see that the peptide bond (-CO-NH) is formed between the amine group of one molecule and the carboxyl group of the adjacent molecule followed by the elimination of a water molecule. This bond is otherwise an amide linkage. When peptide bonds are established among more than ten amino acids, they together form a polypeptide chain. Very often, when a polypeptide chain has a mass exceeding 10000u and the number of amino acids in the chain exceeding 100, we get a protein.
Based on the molecular shape, proteins can be classified into two types –
These are water-insoluble proteins and have fiber-like structure.
Example – keratin
These are water-soluble proteins which have a spherical structure because of coiling of the polypeptide chains.
Classification of protein structure:
Primary structure of protein:
The number of polypeptide chains together form proteins. These chains have amino acids arranged in a particular sequence which is characteristic of the specific protein. Any change in the sequence changes the entire protein.
Secondary structure of protein:
The proteins do not exist in just simple chains of polypeptides. These polypeptide chains usually fold due to the interaction between the amine and carboxyl group of the peptide link. The folding of the polypeptide backbone gives rise to two kinds of shapes:
α – helix: The polypeptide chains twist into a right-handed screw.
β – pleated sheet: In this arrangement, the polypeptide chains are stretched out beside one another and then bonded by intermolecular H-bonds.
Tertiary structure of protein:
This structure arises from further folding of the secondary structure of protein. H-bonds, electrostatic forces, disulphide linkages and Vander Waals forces stabilize this structure.
Quaternary structure of protein:
The spatial arrangement of various tertiary structures gives rise to the quaternary structure.
We have thus gone through the structure of a protein in brief. For the complete understanding, join BYJU’s.