Nucleosides derive their names from the constituent nitrogen bases and sugar molecules they are built of. The four major ribose nucleosides are adenosine, guanosine, cytidine, and uridine; the four major 2-deoxyribose nucleosides are 2-deoxyadenosine, 2-deoxyguanosine, 2-deoxycytidine, and 2-deoxythymine.