(2) Peptide bond: Amino acids in a polypeptide or protein are linked by a peptide bond, which is formed when the carboxyl group ie. COOH of one amino acid reacts with the amino (–NH2) group of the next amino acid with the elimination of a water molecule .
(3) Phosphodiester bond : In a nucleic acid the phosphate group and sugar are joined together by phosphodiester bonds. An bonds is formed between phosphate and pentose sugar molecule in a nucleotide. The bond is called phosphodiester bond because there is an ester bond on either side.
Purines and pyrimidines are manufactured by isolation. They are used by various laboratories, hospitals and research centres.