• Pyrimidine-2, 4 ( 1H, 3H) -dione
  • 2.4 pyrimidinedione

White powdery solid


341 ° C

Moderately soluble in cold water, easily soluble in hot water

-429.4 KJ / mol

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Uracil (U, Ura ) is one of the four main nucleobases in RNA, along with adenine, cytosine and guanine. In DNA, thymine is in its place. Is a heterocyclic organic compound with a Pyrimidingrundgerüst and two keto groups at positions 2 and 4 of uracil nucleosides are uridine into RNA, and the very rare deoxyuridine into the DNA. In the Watson -Crick base pairing, it forms two hydrogen bonds with adenine.


Uracil can be obtained by condensation of urea with 3- pyruvic acid ( " formylacetate " C3H4O3 ). However, the C3 component is not storable in this case and was therefore replaced by malic acid. This is decarbonylated in concentrated sulfuric acid with elimination of water, thus loses carbon monoxide. The in situ generated 3- pyruvic acid condensed with urea in the sulfuric acid solution under two-fold elimination of water.


Uracil is a white powdery solid which melts at 341 ° C.

The compound was discovered during the hydrolytic degradation of nucleic acids. An X-ray crystal structure analysis showed that ( there are several forms of desmotrops ) of the possible tautomeric forms is present in the solid state, the mold - dioxo.

Uracil is a weak acid (pKa = 9.45 ). The acidity constant in the range of phenol (pKa = 10.0 ), and other enols. In the uracil anion, the negative charge is delocalized ( resonance structures ). Therefore, uracil dissolves in aqueous alkalis and aqueous ammonia.

Biological Significance

Uracil is mainly in the body bound to ribose before either one of the nucleotides uridine monophosphate (UMP), uridine diphosphate (UDP) and uridine triphosphate (UTP ), or as part of the ribonucleic acid ( RNA).

Part of the RNA

Uracil forms of the 4- oxo group and the N-H group to adenine base pairing with two hydrogen bonds.

Physiologically uracil is only single-stranded RNA, but not in the double-stranded deoxyribonucleic acid (DNA ) is installed. For pairing with adenine occurs during the transcription in the loops ( loops) of the tRNA during translation and ( protein ).


Uracil forms with riboses two different nucleosides, uridine ( U) ( link via the N1 atom ) and the pseudouridine ( Ψ ) (link via the C5 atom ).


About the phosphorylation of uridine on the C5 atom of the ribose leads to the important nucleotides uridine monophosphate (UMP ), uridine diphosphate (UDP) and uridine triphosphate (UTP).

Comparison of thymine and uracil

Thymine in DNA occurs in the place of uracil. Uracil can be relatively easily produced by deamination and hydrolysis of cytosine, which would amount to a change in the genetic code.

Thymine, however, differs from uracil by an additional methyl group, and can thus not readily cytosine arise. In the existing DNA uracil can thus be identified as mutation and replaced by base excision repair with cytosine. In contrast to DNA, RNA is relatively short-lived, mutated bases in individual RNAs are easily tolerated by the body, which makes use of the simpler to produce uracil appear expedient.

Biochemical Degradation

Uracil is degraded to carbon dioxide (CO2 ) two ammonium ions (NH4 ) and 3- pyruvic acid. The latter reacts further to malonyl- CoA, which can be found for example in the synthesis of fatty acid utilization.

Related compounds