ribose

a sugar of the pentose class which occurs widely in nature as a constituent of nucleosides and several vitamins and enzymes

RNA is made up of nucleotides, which are ribose sugars attached to nitrogenous bases and phosphate groups. The nitrogenous bases include adenine, guanine, uracil, and cytosine. RNA mostly exists in the single-stranded form, but there are special RNA viruses that are double-stranded.