(i) Primary structure of proteins: The sequence in which various amino acids are arranged in a protein is called its primary structure. Any change in the sequence of amino acids creates different protein which alters biological functions.
(ii) Denaturation: When a protein in its native form is subjected to physical change like change in temperature or chemical change like change in pH, the hydrogen bonds are disturbed. Due to this, globules unfold and helix get uncoiled and proteins lose its biological activity. During denaturation 2° and 3° structures of proteins are destroyed but 1° structure remains intact, e.g.coagulation of egg white on boiling.
(iii) Peptide linkage: A peptide linkage is an amide linkage formed between -COOH group of one a-amino acid and -NH2 group of the other amino acid by the elimination of a water molecule.