or "nitrogenous base" - nitrogen-containing molecules present in DNA and RNA: adenine (A), guanine (G), thymine(T), cytosine (C), and uracil (U), which occurs in RNA instead of thymine.
One of the molecules that form DNA and RNA molecules. See also: nucleotide, base pair, base sequence
In biochemistry, one of the four chemical structures made up of carbon, nitrogen, and oxygen molecules in the DNA molecule (adenine, guanine, cytosine, thymine). In the RNA molecule, thymine is replaced by uracil.