In nucleic acids a unit formed by the attachment of a base to 1′ position of sugar is known as nucleoside. When nucleoside is linked to phosphoric acid at 5′ position of sugar moiety nucleotide is obtained. Nuceotides are joined together by phosphodiester linkage between 5′ and 3′ carbon atoms of the pentose sugar. Thus, the sequence in the structure of nucleic acid can be represented as:
The formation o a dinucleotide can be represented as :
In DNA the sugar unit is β-D-2- deoxyribose. Hence, on complete hydrolysis it gives deoxyribose sugar, phosphoric acid and a nitrogen containing heterocyclic base.