3. Purine and Pyrimidine Purines and pyrimidines are nitrogen-containing heterocycles, cyclic compounds whose rings contain both carbon and other elements (hetero atoms).
6. Nucleosides Nucleosides are derivatives of purines and pyrimidines that have a sugar linked to a ring nitrogen. The sugar is linked to the heterocyclic base via a β -N-glycosidic bond, almost always to N-1 of a pyrimidine or to N-9 of a purine.
8. Mononucleotides are nucleosides with a phosphoryl group esterfied to a hydrosyl group of the sugar. 3’- and 5’ –nucleotides are nucleosides with a phosphoryl group on the 3’ – or 5’ –hydroxyl group of the Sugar. Nucleotides Nucleostides are present in all type of cells.