The nucleotide is formed by the union of a phosphate group with a nucleoside. A nucleoside infact contains a sugar molecule alongwith an organic nitrogenous base. Thus, a nucleotide contains an organic nitrogenous base (purine or pyrimidine) alongwith a sugar molecule and a phosphate group, ie,
Nucleoside = Sugar molecule + organic nitrogenous base
Nucleotide = Nucleoside + phosphate group.