A nucleoside is formed when l-position of a pyrimidine (cytosine, thymine or uracil) or 9-position of a purine (guanine or adenine) base is attached to C-l of sugar (ribose or deoxyribose) by a linkage. Thus in general, nucleosides may be represented as: Sugar-Base.

Nucleoside = sugar + base

On the other hand , all the three basic components of nucleic acids (i.e., pentose sugar, phosphoric acid and base) are present in a nucleotide.These are obtained by esterification of C5’ –OH group of the pentose sugar by phosphoric acid. Thus, in general, a nucleotide is represented as:-

Nucleotide= sugar + base + phosphoric acid