Uracil is a pyrimidine, one of the five nitrogenous bases that are part of RNA and is represented by the letter U in the genetic code. Its molecular formula is C4H4N2O2. [1] Uranyl replaces thymine in RNA, which is one of the four nitrogenous bases that make up DNA. Like thymine, uracil is always paired with adenine via two hydrogen bonds, but it lacks the methyl group. It forms the nucleoside uridine (Urd) and the nucleotide uridylate (UMP). Uracil was originally discovered in 1900. It was isolated by hydrolysis of ribonucleic acid from yeast found in certain bovine organs: thymus and spleen, as well as in herring sperm and wheat germ. [2] Uracil is a molecule with a planar structure, unsaturated and with the ability to absorb substances.


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  • 1 Properties
  • 2 Tautomerism
  • 3 Synthesis
  • 4 See also
  • 5 Sources


It is found in RNA, forming a base pair with adenine and being replaced by thymine in DNA. Uracil methylation produces thymine, [4] which, being more stable, protects DNA and improves the efficiency of its replication. Uracil can form a base pair with either base depending on how the Molecule is arranged in the double helix, but it forms more rapidly with adenine due to its methyl group which is repelled in a fixed position. [4] Uracil pairs have been found to bind to adenosine through hydrogen bonds .

Uracil is a hydrogen bond acceptor and can form two of these bonds for each molecule. The uracil can also bind to the sugar of the hydrocarbon skeleton, ribose, forming a ribonucleoside, uridine. When a phosphate binds to uridine, uridine 5′-monophosphate is generated.


Uracil (U) has a tautomeric variant in the form of amide-iminol that is produced thanks to its resonant structure in the substituents of Nitrogen and Oxygen . Due to the instability of the molecule, it has some aromatic property that is partially compensated by the stability of the cycloamide. The keto tautomer is usually the lactam structure, while the enol tautomer is referred to as the lactate structure. These tautomeric forms are predominant in an environment with a pH equal to 7. The lactam structure is the most common form of uracil.

The uracil recycles itself to form nucleotides by carrying out a series of phosphoribosyltransferase-like reactions. The degradation of uracil produces substrates, aspartate, carbon dioxide, and ammonia. [5]

C4H4N2O2 → H3NCH2CH2COO- + NH4 + CO2


There are many ways to synthesize uracil in the laboratory. The first reaction described is the simplest of them all, adding water to the cytosine to produce uracil and ammonia. The most common way to produce uracil is by condensing maleic acid with urea into fuming sulfuric acid, as shown below. Uracil can be synthesized by a double decomposition of thiouracil in chloracetic acid in an aqueous medium.

C4H5N3O + H2O → C4H4N2O2 + NH3 C4H4O4 + CH4N2O → C4H4N2O2 + 2 H2O + CO The photodehydrogenation of 5,6-diuracil, which causes it to be synthesized as beta-alanine, reacts with urea, producing uracil. [6]


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