Thymine // (T, Thy) is one of the four nucleobases in the nucleic acid of DNA that are represented by the letters G–C–A–T. The others are adenine, guanine, and cytosine. Thymine is also known as 5-methyluracil, a pyrimidine nucleobase. In RNA, thymine is replaced by the nucleobase uracil. Thymine was first isolated in 1893 by Albrecht Kossel and Albert Neumann from calves' thymus glands, hence its name.
|Preferred IUPAC name
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||126.115 g·mol−1|
|Density||1.223 g cm−3 (calculated)|
|Melting point||316 to 317 °C (601 to 603 °F; 589 to 590 K)|
|Boiling point||335 °C (635 °F; 608 K) (decomposes)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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As its alternate name (5-methyluracil) suggests, thymine may be derived by methylation of uracil at the 5th carbon. In RNA, thymine is replaced with uracil in most cases. In DNA, thymine (T) binds to adenine (A) via two hydrogen bonds, thereby stabilizing the nucleic acid structures.
Thymine combined with deoxyribose creates the nucleoside deoxythymidine, which is synonymous with the term thymidine. Thymidine can be phosphorylated with up to three phosphoric acid groups, producing dTMP (deoxythymidine monophosphate), dTDP, or dTTP (for the di- and tri- phosphates, respectively).
One of the common mutations of DNA involves two adjacent thymines or cytosine, which, in presence of ultraviolet light, may form thymine dimers, causing "kinks" in the DNA molecule that inhibit normal function.
Thymine could also be a target for actions of 5-fluorouracil (5-FU) in cancer treatment. 5-FU can be a metabolic analog of thymine (in DNA synthesis) or uracil (in RNA synthesis). Substitution of this analog inhibits DNA synthesis in actively dividing cells.
Thymine imbalance causes mutation
During growth of bacteriophage T4, an imbalance of thymine availability, either a deficiency or an excess of thymine, causes increased mutation. The mutations caused by thymine deficiency appear to occur only at AT base pair sites in DNA and are often AT to GC transition mutations. In the bacterium Escherichia coli, thymine deficiency was also found to be mutagenic and cause AT to GC transitions.
In March 2015, NASA scientists reported that, for the first time, complex DNA and RNA organic compounds of life, including uracil, cytosine and thymine, have been formed in the laboratory under outer space conditions, using starting chemicals, such as pyrimidine, found in meteorites. Pyrimidine, like polycyclic aromatic hydrocarbons (PAHs), another carbon-rich compound, may have been formed in red giants or in interstellar dust and gas clouds, according to the scientists. 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 an oxidation reaction with hydrogen peroxide.
- Albrecht Kossel and Albert Neumann (1893) "Ueber das Thymin, ein Spaltungsproduct der Nucleïnsäure" (On thymine, a cleavage product of nucleic acid), Berichte der Deutschen Chemischen Gesellschaft zu Berlin, 26 : 2753-2756. From p. 2754: "Wir bezeichnen diese Substanz als Thymin." (We designate this substance as "thymine" [because it was initially obtained from the thymus glands of calves].)
- Hofreiter M., Serre D., Poinar H.N., Kuch M., and Paabo S. Nature Reviews Genetics (2001) 2:353.
- Bernstein C, Bernstein H, Mufti S, Strom B. Stimulation of mutation in phage T 4 by lesions in gene 32 and by thymidine imbalance. Mutat Res. 1972 Oct;16(2):113-9. doi: 10.1016/0027-5107(72)90171-6. PMID: 4561494
- Smith MD, Green RR, Ripley LS, Drake JW. Thymineless mutagenesis in bacteriophage T4. Genetics. 1973 Jul;74(3):393-403. PMID: 4270369; PMCID: PMC1212957
- Deutch CE, Pauling C. Thymineless mutagenesis in Escherichia coli. J Bacteriol. 1974 Sep;119(3):861-7. doi: 10.1128/JB.119.3.861-867.1974. PMID: 4605383; PMCID: PMC245692
- Marlaire, Ruth (3 March 2015). "NASA Ames Reproduces the Building Blocks of Life in Laboratory". NASA. Retrieved 5 March 2015.
- Tasker, Elizabeth. "Did the Seeds of Life Come from Space?". Scientific American Blog Network. Retrieved 2016-11-24.