Uracil

Uracil is a pyrimidine base and one of the four nucleobases in RNA. Its molecular formula is C4H4N2O2, and it is structurally defined as a 2,4-dioxopyrimidine. In RNA, uracil pairs with adenine through two hydrogen bonds, contributing to the structure and function of RNA molecules.

Uracil is not used in DNA; thymine serves as the corresponding base in DNA. Thymine is chemically a methylated derivative of uracil, and the presence of thymine in DNA helps distinguish DNA from RNA and reduces the mutational impact of cytosine deamination.

Biosynthesis and salvage: Uracil is produced in de novo pyrimidine biosynthesis as part of the pathway that forms uridine monophosphate (UMP). Cells can also salvage uracil by attaching it to ribose-5-phosphate via uracil phosphoribosyltransferase to generate UMP, providing a readily usable nucleotide.

Degradation and metabolism: In many organisms, uracil is degraded through a uracil catabolic pathway that ultimately yields beta-alanine and related metabolites. In humans, enzymes such as dihydropyrimidine dehydrogenase and dihydropyrimidinase participate in this breakdown.

Medical relevance: Uracil derivatives have medical and research applications. For example, 5-fluorouracil is a chemotherapy agent that is metabolized to active nucleotides; these metabolites inhibit thymidylate synthase and can be incorporated into RNA, disrupting nucleic acid synthesis in cancer cells.