The base of a nucleotide is joined covalently in an N-β-glycosyl bond to the 1′ carbon of the pentose sugar, and the phosphate is esterified to 5′ carbon. The N-β-glycosyl bond is formed by removal of water, as in O-glycosidic bond formation. The nitrogenous bases present in nucleic acids are:
1) Purines: Adenine and guanine
2) Pyrimidines: Cytosine, thymine and uracil.
The main function of nucleic acids is the storage of information for all life processes and its expression.