uracyl

Uracil, sometimes spelled uracyl, is one of the four standard nucleobases in RNA. It belongs to the pyrimidine class and has the chemical identity 2,4-dioxopyrimidine with the formula C4H4N2O2. In physiological conditions, the keto form is predominant.

In RNA, uracil pairs with adenine through two hydrogen bonds, contributing to the encoding of genetic information and to the structure and function of RNA molecules. Unlike DNA, which uses thymine, RNA typically contains uracil. Thymine, with a methyl group, provides greater stability in DNA. Uracil also signals RNA processing and turnover; cytosine can deaminate to uracil in DNA, a lesion repaired by uracil-DNA glycosylase.

Uracil is produced in cells via the de novo pyrimidine biosynthesis pathway, yielding uridine monophosphate (UMP), which is subsequently phosphorylated to UDP and UTP for use in RNA synthesis. Uracil can also be salvaged from degraded RNA or generated by deamination of cytosine, with enzymes converting it back into activated nucleotides.

In addition to its role as a base, uracil forms the nucleoside uridine when attached to ribose, and various nucleotide derivatives such as UMP, UDP, and UTP. Uracil derivatives have applications in research and medicine. A notable example is 5-fluorouracil, a uracil analogue used in cancer chemotherapy that inhibits thymidylate synthase and disrupts DNA synthesis.

Uracil is widely distributed in living organisms as a fundamental component of RNA, with its metabolism and regulation linked to broader nucleotide pathways.