A pentose sugar with the attached nitrogen base forms a nucleoside.
A nucleoside is formed when 1-position of a pyrimidine (cytosine, thiamine or uracil) or 9-position of a purine (guanine or adenine) base is attached to carbon 1 of sugar (ribose or deoxyribose) by a β-linkage.
Sugar + Nitrogen Base = Nucleoside
