Uracil. Computer artwork of a molecule of uracil (2, 6-dioxytetrahydropyrimidine). This is a pyrimidine-derived nucleic acid found in RNA (ribonucleic acid). The atoms shown as cylinders are colour coded: carbon (green), nitrogen (blue), hydrogen (white) and oxygen (red). Uracil is one of the four bases found in RNA (along with adenine, cytosine and guanine). Unlike the other bases, uracil does not occur in DNA. The positioning of these bases along the RNA chain is what is known as the genetic code. Each genetic code is unique and it is this which gives organisms their individual characteristics.