Thymine. Computer artwork of a molecule of thymine (2, 4-dihydroxy-5-methylpyrimidine). This is a pyrimidine-derived nucleic acid found in DNA (deoxyribonucleic acid). The atoms shown as cylinders are colour coded: carbon (green), nitrogen (blue), hydrogen (white) and oxygen (red). Thymine is one of the four bases found in DNA (along with adenine, cytosine and guanine). Unlike the other bases, thymine does not occur in RNA. The positioning of these bases along the DNA chain is what is known as the genetic code. Each genetic code is unique and it is this which gives organisms their individual characteristics.