Each nucleoside triphosphate is made up of three phosphates (represented here by yellow spheres), a deoxyribose sugar (beige rectangle) and one of four bases (differently colored cylinders).

Deoxynucleoside analogues such as 5-aza-2-deoxycytidine (depicted by Z) are converted into the triphosphate inside S-phase cells and are incorporated in place of cytosine into DNA. Ribonucleosides ...