Two types of sugar are present in the nucleic acids; D-ribose is the parent sugar present in the RNA, whereas D-2-deoxyribose is a derivative in which the OH group on C-2 has been replaced by an H atom. The two sugars are differentiated by specific colour reactions. Ribose reacts with orcinol in hydrochloric acid solution containing ferric chloride. Deoxyribose reacts with diphenylamine in acid solution.

Pentose reacts with phosphoric acid and forms esters. The OH groups of the pentose at C-3 and C-5 are involved in forming 3′-5′-phosphodiester bond between adjacent pentose residues. This phosphodiester bond is an integral part of the structure of nucleic acids.