1. any of various compounds consisting of a sugar, usually ribose or deoxyribose, and a purine or pyrimidine base, especially a compound obtained by hydrolysis of a nucleic acid, such as adenosine or guanine.

1. an organic molecule in which a nitrogenous heterocyclic base (or nucleobase), which can be either a double-ringed purine or a single-ringed pyrimidine, is covalently attached to a five-carbon pentose sugar (deoxyribose in dna or ribose in RNA). when the phosphate group is covalently attached to the pentose sugar, it forms a nucleotide.

1. A type of molecule found in all living organisms, present mostly in chemically combined form as a component of nucleic acids, and also in smaller amounts in free form, consisting of a pentose sugar bound to a purine or pyrimidine base; two types of nucleoside, ribonucleoside and deoxyribonucleoside, are present. the most common bases present in nucleosides are adenine, cytosine, uracil, guanine, and thymine, and to a lesser extent hypoxanthine and other bases are found. the most commmon ribonucleosides composed from these bases are called adenosine, cytidine, uridine, and guanosine. the forms esterified with orthophosphoric at the 5-position of the pentose are called nucleotides. the nucleotides form the monomer units which are combined into dna and RNA, which carry the genetic information required for reproduction in all known organisms.

1. a glycoside formed by partial hydrolysis of a nucleic acid