Thymine
- 5 - methyluracil
- 2,4 -dioxo -5- methylpyrimidin (IUPAC)
- 5-methyl- 2, 4 ( 1H, 3H) -pyrimidinedione
White crystalline solid
Fixed
1.46 g · cm -3
316-317 ° C
Template: Infobox chemical / molecular formula search available
Thymine (T, Thy, 5 - methyluracil ) is one of the four main nucleobases in DNA, along with adenine, cytosine and guanine. In RNA, uracil stands in its place. Is a heterocyclic organic compound with a Pyrimidingrundgerüst and two keto groups at positions 2 and 4 and the methyl group at position 5 of the nucleosides are deoxythymidine thymine in the DNA and RNA in the rare ribothymidine (eg in the tRNA ). In the Watson -Crick base pairing, it forms two hydrogen bonds with adenine.
- 3.1 nucleosides
- 3.2 nucleotides
- 3.3 part of the DNA
- 3.4 Comparison of thymine and uracil
- 3.5 thymine dimer
Representation and extraction
Isolation can be done from bovine brains or cod roe.
A synthetic representation of can be achieved by cyclization of N -ethoxycarbonyl -3-methoxy -2-methyl -acrylamide in aqueous ammonia solution.
Another synthesis starts from 3-methyl malic acid, which is decarboxylated in fuming sulfuric acid, and condensed with urea.
Properties
Physical Properties
Thymine is brilliant, bitter-tasting, acicular or prismatic crystals, melting at 335-337 ° C with decomposition. The compound is readily soluble in hot water, in alcohol and ether, the solubility is low. In alkaline media it dissolves to form a salt of an enolate derived from a result of the enol form of 5-methyl -2 ,4- pyrimidindiol.
Chemical Properties
In principle, there may be thymine in six tautomeric structures. The lactam (1) is however preferred with respect to the enol forms.
Biological Significance
Thymine can be part of the DNA or different nucleosides and nucleotides.
Nucleosides
About the N1 atom of the ring thymine can be bound N- glycosidically linked to the C1 atom of the deoxyribose; this is called a nucleoside, the deoxythymidine. When bound to the ribose nucleoside ribothymidine formed.
Nucleotides
About the phosphorylation of thymidine on the C5 atom of the ribose leads to the important nucleotides Desoxythymidinmonophosphat ( dTMP ), Desoxythymidindiphosphat ( dTDP ) and deoxythymidine triphosphate ( dTTP ).
Part of the DNA
In the DNA double helix, thymine forms over the 4 - oxo group and the N3 -H group of two hydrogen bonds with the corresponding adenine base of the complementary strand.
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.
Thymine dimer
For thymine dimers is a DNA mutation which is induced by UV radiation. Here, two connect on a DNA strand adjacent thymine bases by a [2 2 ] cycloaddition covalently to form a dimer, which is a relatively stable cyclobutane derivative.
Particularly susceptible to such a mutation are the skin cells, which are exposed to sunlight. For this reason, thymine dimers are discussed as a major cause for the development of skin cancer.
Use
Thymine serves as a source of some drugs such as zidovudine, telbivudine and Clevudin.