molecule consisting of a nitrogenous base (adenine, guanine, thymine, or
cytosine in DNA; adenine, guanine, uracil, or cytosine in RNA), a phosphate
group, and a sugar (deoxyribose in DNA; ribose in RNA). DNA and RNA are polymers
of many nucleotides.
Definition from: GeneReviews
from the University of Washington and the National Center for Biotechnology Information
A nucleotide is the basic building block of nucleic acids. RNA and DNA are polymers made of long chains of nucleotides. A nucleotide consists of a sugar molecule (either ribose in RNA or deoxyribose in DNA) attached to a phosphate group and a nitrogen-containing base. The bases used in DNA are adenine (A), cytosine (C), guanine (G), and thymine (T). In RNA, the base uracil (U) takes the place of thymine.