What is Thymine?

Thymine, which is often abbreviated to T or Thy, can also be referred to as 5-methyluracil. It is one of the pyrimidine bases found in the nucleic acid of DNA, along with adenine, guanine and cytosine (A, G and C). These bases are the building blocks of DNA and life form on earth.

Albrecht Kossel and Albert Neumann discovered thymine in 1893 when they successfully isolated thymine from the thymus glands of calves for the first time in history.

Chemical Structure

The chemical structure of thymine contains the ring-shaped pyrimidine molecule, similarly to each of the nucleobases.

In the formation of DNA, thymine and adenine are always paired together by the force of two hydrogen bonds, which creates a stable nucleic acid structure. In a comparable fashion, guanine and cytosine bind together in the creation of DNA. Under specific conditions, such as exposure to ultraviolet light, thymine dimers may also occur, although this is much less common that the thymine-adenine pairing. In most cases, thymine is not present in RNA structures because it is replaced by uracil.

The scientific name of thymine, 5-methyluracil, implies that it can be derived with methylation process of uracil at the position of the 5th carbon. Specifically in the chemical structure, this means that a methyl- branch (-CH3) is added to the pyrimidine ring.


When combined with deoxyribose, thymine forms the nucleoside deoxythymidine, which is also known more commonly as thymidine.

This can undergo phosphorylation with the addition of phosphoric acid groups to form thymidine monophosphate, thymidine diphosphate, or thymidine triphosphate, depending on the number of phosphoric acid groups added.

Mutation and Cancer

If the natural chemical structure of thymine is defected, the DNA is mutated, which can lead to the formation of melanoma.

A common cause of DNA mutation involving thymine is the response to ultraviolet light. Light waves at this frequency can cause to thymine bases next to each other to form a dimer. As this is not the natural structure of the DNA, this can alter the functionality of the DNA and may result in deregulation of cell growth and possible growth of cancerous cells.

5-fluorouracil is a common cancer treatment that may target thymine in its mechanism of action. Pharmacologically, this drug can be a metabolic analog of thymine in the synthesis of DNA. If 5-fluoruracil is incorporated into the DNA of actively dividing cancer cells, the synthesis of new DNA and cancer cells is inhibited.

Thymine in Space

In 2015, NASA scientists reported that evidence of thymine had been formed in a laboratory under conditions that simulated outer space.

Meteorites often contain chemical substances such as pyrimidine polycyclic aromatic hydrocarbons, so this was used as a starting base in the laboratory. Under simulated conditions, the scientists were able to produce thymine, uracil and cytosine. These nucleobases form a considerable sector of the building blocks of life, suggesting that under specific conditions in outer space life form could be created. To date, this is purely theoretical but further research is needed.


  • http://gallica.bnf.fr/ark:/12148/bpt6k90730p/f455.image
  • http://www.nasa.gov/content/nasa-ames-reproduces-the-building-blocks-of-life-in-laboratory
  • http://www.cell.com/cell/abstract/S0092-8674(11)00662-3?_returnURL=http%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0092867411006623%3Fshowall%3Dtrue
  • http://pubchem.ncbi.nlm.nih.gov/compound/thymine#section=Classification

Further Reading

  • All Thymine Content

Last Updated: Aug 23, 2018

Written by

Yolanda Smith

Yolanda graduated with a Bachelor of Pharmacy at the University of South Australia and has experience working in both Australia and Italy. She is passionate about how medicine, diet and lifestyle affect our health and enjoys helping people understand this. In her spare time she loves to explore the world and learn about new cultures and languages.

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