uracil , organic base of the pyrimidine family. It was isolated from herring sperm and also produced in a laboratory in 1900-1901. When combined with the sugar ribose in a glycosidic linkage, uracil forms a derivative called uridine (a nucleoside), which in turn can be phosphorylated with from one to three phosphoric acid groups, yielding respectively the three nucleotides UMP (uridine monophosphate), UDP (uridine diphosphate), and UTP (uridine triphosphate). The analogous nucleosides and nucleotides formed from uridine and deoxyribose occur only very rarely in living systems; such is not the case with the other pyrimidines. The nucleotide derivatives of uracil perform important functions in cellular metabolism, particularly in carbohydrate metabolism; UTP acts as a coenzyme in the biosynthesis of sucrose in plants, lactose and glycogen in mammals, and chitin in insects. It can also readily donate one of its phosphate groups to adenosine diphosphate (ADP) to form adenosine triphosphate (ATP), an extremely important intermediate in the transfer of chemical energy in living cells. Since the uracil nucleotides contain only ribose and not deoxyribose, UTP is the source of uridine only in ribonucleic acid (RNA); there is no uridine in deoxyribonucleic acid (DNA). Its involvement in the biosynthesis of RNA demonstrates that uracil is important in the translation of genetic information (see nucleic acid ). A few laboratory derivatives of uracil have been designed as...