a colourless, crystalline organic compound of the pyrimidine family that occurs as a component of ribonucleic acid ( RNA), a molecule involved in the transmission of hereditary characteristics. The RNA molecule consists of a sequence of nucleotides, each containing a five-carbon sugar (ribose), a phosphate group, and a nitrogenous base. Uracil is one of four nitrogenous bases found in the RNA molecule: uracil and cytosine (derived from pyrimidine) and adenine and guanine (derived from purine). Deoxyribonucleic acid ( DNA) also contains each of these nitrogenous bases, except that thymine is substituted for uracil. During the synthesis of an RNA strand from a DNA template (transcription), uracil pairs only with adenine, and guanine pairs only with cytosine.

Uracil is also a component of several coenzymes that act in conjunction with enzymes in several processes of carbohydrate metabolism.