What is Uracil?

It is an organic primary nucleobase occurring only in RNA with a formula of C₄H₄N₂O₂ and pairs complementary with adenine. It has a molar mass of 112.08676 g/mol.

The monomeric nucleotides form polymers of nucleic acid-like RNA and DNA. Each nucleotide is comprised of nucleobase, a pentose sugar, and a phosphoric.

Guanine, Adenine, Cytosine, Uracil, and Thymine are the 5 fundamental nucleobases that comprise basic units of genetic code. Nucleobases can be pyrimidine or purine. Uracil is an example of a pyrimidine base.

Uracil Properties

Uracil like other pyrimidines is an aromatic heterocyclic compound with a pyrimidine ring that comprises alternating nitrogen and carbon atoms. Uracil has a melting point of 335 °C. It is a part of both nucleosides and a nucleotide. It under normal conditions is not seen in DNA but is present in RNA replacing thymine.

Uracil vs Thymine

Pyrimidine nucleobases include thymine, cytosine, and uracil. Structurally uracil and thymine are similar except for a methyl group present at position 5 in the aromatic ring in thymine. Through complementary base pairing, it bonds with adenine via 2 hydrogen bonds.

In DNA thymine is present, it at 2^nd and 4^th position consists of keto groups, and at 5th position a methyl group in the ring. Thymine pairs with adenine in DNA with the hep of hydrogen bonds.

Uracil is absent in DNA as it can destabilize DNA and repair systems in DNA cannot distinguish between deaminated cytosine that turns into uracil and the original uracil. This can lead to point mutations if not repaired.

Cytosine is structurally different from uracil in having an amine group at position 4 and a keto group at position 2 in its heterocyclic ring and has a formula of C₄H₅N₃O. It occurs in both types of nucleic acids and it pairs up with guanine.

Biosynthesis of Uracil

Pyrimidine formation is initiated with the compound carbamoyl phosphate that is formed in a reaction catalyzed by enzyme carbamoyl phosphate synthetase. Further the following series of reaction occur:

carbamoyl phosphate>> carbamoyl asparatate>> dihydroorate>> orotate>> OMP. Orotidine-5-monophosphate or OMP yields uridine monophosphate on decarboxylation.

Ultimately by the activity of kinases and dephosphorylation of ATPs, at the end of the pathway, UDP and UTP are formed. UTP is aminated in the presence of the enzyme CTP synthetase to produce CTP.

Uracil when attached to a deoxyribose sugar is called uridine and when phosphorylated with 3 phosphoric acid groups, it becomes uridine triphosphate or UTP. UTP constitutes one of the primary monomeric building units that comprise RNA.

Degradation of uracil occurs in steps. It is converted first into β-alanine that is then degraded into malonyl-CoA. This can be utilized in the synthesis of fatty acids. If it is degraded further it will lead to the formation of ammonium along with CO2 and water. This ammonium is further processed in the urea cycle.

Uracil is recycled via the salvage pathway. For example, it reacts with ribose-1-phosphate in presence of the enzyme uridine phosphorylase to produce UMP.

Biological Function of Uracil

Uracil aids in the formation of nucleotides like UDP, UMP, and UTP. The naming of nucleotides depends on the number of phosphate groups attached to them. The nucleotide UDP is important for glycogenesis. UDP is formed when glucose-1-phosphate combines with UTP.

Glycogen is synthesized when enzyme glycogen synthase combining individual UDP-glucose units. As these UDP-glucose are added, UDP is cleaved. Therefore, UDP aids in the formation of glycogen from glucose in the liver and muscle cells.

UTP is important in transcription as it is the direct precursor of RNA. Uracil aids in the formation of nucleotides like UDP, UMP, and UTP. The naming of nucleotides depends on the number of phosphate groups attached to them.

The nucleotide UDP is important for glycogenesis. UDP is formed when glucose-1-phosphate combines with UTP. Glycogen is synthesized when enzyme glycogen synthase combining individual UDP-glucose units.

As these UDP-glucose are added, UDP is cleaved. Therefore, UDP aids in the formation of glycogen from glucose in the liver and muscle cells. UTP is important in transcription as it is the direct precursor of RNA.