Science, Tech, Math › Science Thymine Definition, Facts, and Functions Share Flipboard Email Print Thymine is one of the pyrimidine bases found in DNA. Malachy120 / Getty Images Science Chemistry Biochemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated January 13, 2020 Thymine is one of the nitrogenous bases used to build nucleic acids. Along with cytosine, it is one of the two pyrimidine bases found in DNA. In RNA, it is usually replaced by uracil, but transfer RNA (tRNA) contains trace amounts of thymine. Chemical Data: Thymine IUPAC Name: 5-Methylpyrimidine-2,4(1H,3H)-dioneOther Names: Thymine, 5-methyluracilCAS Number: 65-71-4Chemical Formula: C5H6N2O2Molar Mass: 126.115 g/molDensity: 1.223 g/cm3Appearance: White powderSolubility in Water: MiscibleMelting Point: 316 to 317 °C (601 to 603 °F; 589 to 590 K)Boiling Point: 335 °C (635 °F; 608 K) (decomposes)pKa (Acidity): 9.7Safety: Dust may irritate eyes and mucous membranes Thymine is also called 5-methyluracil or it may be represented by the capital letter "T" or by its three-letter abbreviation, Thy. The molecule gets its name from its initial isolation from calf thymus glands by Albrecht Kossel and Albert Neumann in 1893. Thymine is found in both prokaryotic and eukaryotic cells, but it does not occur in RNA viruses. Key Takeaways: Thymine Thymine is one of the five bases used to build nucleic acids.It is also known as 5-methyluracil or by the abbreviations T or Thy.Thymine is found in DNA, where it pairs with adenine via two hydrogen bonds. In RNA, thymine is replaced by uracil.Ultraviolet light exposure causes a common DNA mutation where two adjacent thymine molecules form a dimer. While the body has natural repair processes to correct the mutation, unrepaired dimers can lead to melanoma. Chemical Structure The chemical formula of thymine is C5H6N2O2. It forms a six-member heterocyclic ring. A heterocyclic compound contains atoms besides carbon within the ring. In thymine, the ring contains nitrogen atoms at the 1 and 3 positions. Like other purines and pyrimidines, thymine is aromatic. That is, its ring includes unsaturated chemical bonds or lone pairs. Thymine combines with the sugar deoxyribose to form thymidine. Thymidine may be phosphorylated with up to three phosphoric acid groups to form deoxythymidine monophosphate (dDMP), deoxythymidine diphosphate (dTDP), and deoxythymidine triphosphate (dTTP). In DNA, thymine forms two hydrogen bonds with adenine. The phosphate of the nucleotides forms the backbone of the DNA double helix, while the hydrogen bonds between the bases run through the center of the helix and stabilize the molecule. Thymine forms two hydrogen bonds with adenine in DNA. Volodymyr Horbovyy / Getty Images Mutation and Cancer In the presence of ultraviolet light, two adjacent thymine molecules often mutate to form a thymine dimer. A dimer kinks the DNA molecule, affecting its function, plus the dimer cannot be correctly transcribed (replicated) or translated (used as a template to make amino acids). In a single skin cell, up to 50 or 100 dimers may form per second upon exposure to sunlight. Uncorrected lesions are the leading cause of melanoma in humans. However, most dimers are fixed by nucleotide excision repair or by photolyase reactivation. While thymine dimers may lead to cancer, thymine may also be used as a target for cancer treatments. Introduction of the metabolic analog 5-fluorouracil (5-FU) substitutes 5-FU for thymine and prevents cancer cells from replicating DNA and dividing. In the Universe In 2015, researchers at Ames Laboratory successfully formed thymine, uracil, and cytosine under laboratory conditions simulating outer space using pyrimidines as a source material. Pyrimidines naturally occur in meteorites and are believed to be formed in gas clouds and red giant stars. Thymine has not been detected in meteorites, possibly because it is oxidized by hydrogen peroxide. However, the lab synthesis demonstrates the building blocks of DNA may be transported to planets by meteorites. Sources Friedberg. Errol C. (January 23, 2003). "DNA Damage and Repair." Nature. 421 (6921): 436–439. doi:10.1038/nature01408Kakkar, R.; Garg, R. (2003). “Theoretical study of the effect of radiation on thymine.” Journal of Molecular Structure-TheoChem 620(2-3): 139-147.Kossel, Albrecht; Neumann, Albert (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.Marlaire, Ruth (March 3, 2015). "NASA Ames Reproduces the Building Blocks of Life in Laboratory." NASA.gov.Reynisson, J.; Steenken, S. (2002). “DFT studies on the pairing abilities of the one-electron reduced or oxidized adenine-thymine base pair.” Physical Chemistry Chemical Physics 4(21): 5353-5358.