A macromolecule formed of repeating riboses linked by phosphodiester bonds between the 3-hydroxyl group of one and the 5-hydroxyl group of the next. A purine, adenine or guanine, or a pyrimidine, cytidine or uracil, is held in a glycosidic bond to the anomeric carbon of the sugar. RNA has several biological functions, most of which depend upon its ability to form sequence-specific interactions with DNA. RNA comprises the genome of some viruses, and in some cases can perform some elementary catalytic functions.