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Nucleotides (NT's) are the building block from which RNA and DNA are constructed. Each nucleotide consists of a nitrogen-containing base, a sugar, and a phosphate group. Nucleotides are connected by bonds between the phosphate group and sugar. The four most common bases in RNA are adenine (A), guanine (G), cytosine (C), and uracil (U). When the base is bound to ribose, a nucleoside is created. The addition of a phosphate group to a nucleoside creates a a nucleotide. Other bases modified bases such as xanthine, hypoxanthine, and 5,6 dihydrouracil are present in certain RNAs.

Comparison to DNA

Main Article: Comparison of RNA and DNA


The chemical composition of RNA and DNA differ in two small, but significant ways. In RNA, the sugar ribose is present. In DNA, the closely related sugar 2'-deoxyribose is present. These two sugars differ in the presence of an -OH group at the 2' position of the sugar.

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In DNA, uracil is replaced by its close relative thymine, or 5-methyluracil. Thymine contains a methyl group in place of a hydrogen at the 5-position of the pyrimidine ring.

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Roles of Nucleotides

In addition to their role in RNA and DNA, nucleotides also serve as energy-storage molecules, enzyme cofactors, and signaling molecules.