Nucleosides

A nucleoside consists simply of a nucleobase (also termed a nitrogenous base) and a five-carbon sugar (ribose or 2'-deoxyribose). According to the structure of pentose, it can be divided into two categories: Ribonucleoside and Deoxyribonucleoside. There are three free hydroxyl groups on the Ribonucleoside; There are only two free hydroxyl groups on Deoxyribonucleoside.