(i) A peptide linkage is an amide (—CO— NH —) linkage formed between —COOH group of one aamino acid and —NH2 group of other a-amino acid by loss of a water molecule.
(ii) The specific sequence in which various a-amino acids present in a protein are linked to one another is called its primary structure. Any change in its primary structure creates a new protein.
(iii) Denaturation of Proteins: When a protein in its native form is subjected to a change, such as change in temperature or change in pH, the hydrogen bonds are disturbed. Due to this, globules unfold and helix get uncoiled and protein loses its biological activity. This is called denaturation of protein. During denaturation, 2° and 3° structures are destroyed but 1° structures remain intact, e.g., coagulation of egg while on boiling, curdling of milk, etc.