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Organic compound of the pyrimidine family, often called a base, consisting of a single ring, containing both nitrogen and carbon atoms, and an amino group. It occurs in combined form in nucleic acids and several coenzymes. In DNA its complementary base is guanine. It or its corresponding nucleoside or nucleotide may be prepared from DNA by selective techniques of hydrolysis.
This entry comes from Encyclopædia Britannica Concise. For the full entry on cytosine, visit Britannica.com.