As its alternate name (5-methyluracil) suggests, thymine may be derived bymethylation of uracil at the 5th carbon. InRNA, thymine is replaced withuracil in most cases. In DNA, thymine (T) binds toadenine (A) via two hydrogen bonds, thereby stabilizing the nucleic acid structures.
Thymine combined withdeoxyribose creates thenucleosidedeoxythymidine, which is synonymous with the termthymidine. Thymidine can be phosphorylated with up to three phosphoric acid groups, producingdTMP (deoxythymidinemonophosphate),dTDP, ordTTP (for thedi- andtri- phosphates, respectively).
One of the common mutations of DNA involves two adjacent thymines or cytosine, which, in presence ofultraviolet light, may formthymine dimers, causing "kinks" in the DNA molecule that inhibit normal function.
Thymine could also be a target for actions of 5-fluorouracil (5-FU) incancer treatment. 5-FU can be a metabolic analog of thymine (in DNA synthesis) or uracil (in RNA synthesis). Substitution of this analog inhibitsDNA synthesis in actively dividing cells.
Thymine bases are frequently oxidized tohydantoins over time after the death of an organism.[3]
During growth ofbacteriophage T4, an imbalance of thymine availability, either a deficiency or an excess of thymine, causes increasedmutation.[4] The mutations caused by thymine deficiency appear to occur only at ATbase pair sites in DNA and are often AT to GCtransition mutations.[5] In the bacteriumEscherichia coli, thymine deficiency was also found to cause the same mutation.[6]
In March 2015, NASA scientists reported that, for the first time, complexDNA andRNAorganic compounds oflife, includinguracil,cytosine and thymine, have been formed in the laboratory underouter space conditions, using starting chemicals, such aspyrimidine, found inmeteorites. Pyrimidine, likepolycyclic aromatic hydrocarbons (PAHs), another carbon-rich compound, may have been formed inred giants or ininterstellar dust and gas clouds, according to the scientists.[7] Thymine has not been found in meteorites, which suggests the first strands of DNA had to look elsewhere to obtain this building block. Thymine likely formed within some meteorite parent bodies, but may not have persisted within these bodies due to anoxidation reaction withhydrogen peroxide.[8]
Thymine was first prepared by hydrolysis of the correspondingnucleoside obtained from natural sources. Interest in its direct chemical synthesis began in the early 1900s:Emil Fischer published a method starting fromurea but a more practical synthesis used methylisothiourea in acondensation reaction with ethyl formyl propionate, followed by hydrolysis of the pyrimidine intermediate:[9]
Many other preparative methods have been developed, including optimised conditions so that urea can be used directly in the reaction shown above, preferably with methyl formyl propionate.[10]
^Bernstein, Carol; Bernstein, Harris; Mufti, Siraj; Strom, Barbara (October 1972). "Stimulation of mutation in phage T 4 by lesions in gene 32 and by thymidine imbalance".Mutat. Res.16 (2):113–119.doi:10.1016/0027-5107(72)90171-6.PMID4561494.
^Guo, Xianghai; Shen, Jiaxiang (2014). "An environmentally benign approach to the synthesis of thymine via hydroformylation of methyl acrylate".Monatshefte für Chemie - Chemical Monthly.145 (4):657–661.doi:10.1007/s00706-013-1128-y.S2CID97367180.
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