What is the difference between a nucleoside and a nucleotide?

Explanation

A nucleoside is formed when 1- position of a pyrimidine (cytosine , thymine or uracil) or 9-position of a purine (guannine or adenine) base is attached to C-1 of sugar (ribose or deoxyribose ) by a `beta`-linkage. Thus , in general , nucleosides may be represented as : Sugar -Base. For exaple , structure (I) represents a nucleoside.

A nucleoside contains all the three basic components of nucleic acids ,i.e., a phosphoric acid group , a pentose sugar and a nitrogenous base. These are obtained by estertification of `C_(5)'-OH` group of the pentose sugar by phosphoric acid. Thus , in general , a nucleotide is represented as
`"Sugar -Base" -O-overset(O)overset(||)underset(O)underset(||)P-OH`
For example , structure (II) represents a nucleotide.