Thymidine (

symbol A symbol is a mark, sign, or word that indicates, signifies, or is understood as representing an idea, object, or relationship. Symbols allow people to go beyond what is known or seen by creating linkages between otherwise very different conc ...

dT or dThd), also known as deoxythymidine, deoxyribosylthymine, or thymine deoxyriboside, is a pyrimidine deoxynucleoside. Deoxythymidine is the DNA nucleoside T, which pairs with deoxyadenosine (A) in double-stranded DNA. In cell biology it is used to

synchronize Synchronization is the coordination of events to operate a system in unison. For example, the conductor of an orchestra keeps the orchestra synchronized or ''in time''. Systems that operate with all parts in synchrony are said to be synchronou ...

the cells in G1/early S phase. The prefix deoxy- is often left out since there are no precursors of thymine nucleotides involved in RNA synthesis. Before the boom in thymidine use caused by the need for thymidine in the production of the antiretroviral drug azidothymidine (AZT), much of the world's thymidine production came from

herring Herring are forage fish, mostly belonging to the family of Clupeidae. Herring often move in large schools around fishing banks and near the coast, found particularly in shallow, temperate waters of the North Pacific and North Atlantic Ocea ...

sperm. Thymidine occurs almost exclusively in DNA but it also occurs in the

T-loop Audio induction loop systems, also called audio-frequency induction loops (AFILs) or hearing loops, are an assistive listening technology for individuals with reduced ranges of hearing. A hearing loop consists of one or more physical loop of ca ...

tRNA Transfer RNA (abbreviated tRNA and formerly referred to as sRNA, for soluble RNA) is an adaptor molecule composed of RNA, typically 76 to 90 nucleotides in length (in eukaryotes), that serves as the physical link between the mRNA and the amino a ...

Structure and properties

In its composition, deoxythymidine is a nucleoside composed of

deoxyribose Deoxyribose, or more precisely 2-deoxyribose, is a monosaccharide with idealized formula H−(C=O)−(CH2)−(CHOH)3−H. Its name indicates that it is a deoxy sugar, meaning that it is derived from the sugar ribose by loss of a hydroxy group ...

(a pentose sugar) joined to the pyrimidine base thymine. Deoxythymidine can be phosphorylated with one, two or three phosphoric acid groups, creating dTMP (deoxythymidine monophosphate), dTDP, or dTTP (for the di- and tri- phosphates, respectively). It exists in

solid Solid is one of the four fundamental states of matter (the others being liquid, gas, and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structura ...

form as small white crystals or white crystalline powder. It has a

molecular weight A molecule is a group of two or more atoms held together by attractive forces known as chemical bonds; depending on context, the term may or may not include ions which satisfy this criterion. In quantum physics, organic chemistry, and bioch ...

of 242.229 u and a

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends ...

of 185

°C The degree Celsius is the unit of temperature on the Celsius scale (originally known as the centigrade scale outside Sweden), one of two temperature scales used in the International System of Units (SI), the other being the Kelvin scale. The d ...

. The stability of deoxythymidine under

standard temperature and pressure Standard temperature and pressure (STP) are standard sets of conditions for experimental measurements to be established to allow comparisons to be made between different sets of data. The most used standards are those of the International Union ...

(STP) is very high. Deoxythymidine is non-toxic and as part of one of the four nucleosides in DNA it is a naturally occurring compound that exists in all living organisms and DNA viruses. Instead of thymidine, RNA contains uridine (

uracil Uracil () (symbol U or Ura) is one of the four nucleobases in the nucleic acid RNA. The others are adenine (A), cytosine (C), and guanine (G). In RNA, uracil binds to adenine via two hydrogen bonds. In DNA, the uracil nucleobase is replaced ...

joined to ribose). Uracil is chemically very similar to thymine, which is also known as 5-methyluracil. Since thymine nucleotides are precursors of DNA (but not RNA), the prefix "deoxy" is often left out, i.e., deoxythymidine is often just called thymidine. Thymidine is listed as a chemical teratogen.

Modified analogs

Iododeoxyuridine is a radiosensitizer and increases the amount of DNA damage received from ionizing radiation. Azidothymidine (AZT) – used in the treatment of

HIV The human immunodeficiency viruses (HIV) are two species of '' Lentivirus'' (a subgroup of retrovirus) that infect humans. Over time, they cause acquired immunodeficiency syndrome (AIDS), a condition in which progressive failure of the immu ...

infection. AZT inhibits the process of reverse transcription, a critical step in the

viral life cycle Viruses are only able to replicate themselves by commandeering the reproductive apparatus of cells and making them reproduce the virus's genetic structure and particles instead. How viruses do this depends mainly on the type of nucleic acid DNA ...

. Radiolabeled thymidine (TdR), such as tritiated thymidine (³H-TdR), is commonly used in cell proliferation assays. The thymidine is incorporated into dividing cells and the level of this incorporation, measured using a liquid scintillation counter, is proportional to the amount of cell proliferation. For example, lymphocyte proliferation can be measured this way in lymphoproliferative disorders. Bromodeoxyuridine (BrdU) is another thymidine analog that is often used for the detection of proliferating cells in living tissues. 5-Ethynyl-2´-deoxyuridine (EdU) is a thymidine analog which is incorporated into the DNA of dividing cells and is used to assay DNA synthesis in cell culture or living tissues. It can be visualized by covalently binding a fluorescent azide using

click chemistry In chemical synthesis, click chemistry is a class of biocompatible small molecule reactions commonly used in bioconjugation, allowing the joining of substrates of choice with specific biomolecules. Click chemistry is not a single specific reactio ...

, which is less harsh than the conditions used to expose the epitope for BrdU antibodies.

Edoxudine Edoxudine (or edoxudin) is an antiviral drug. It is an analog of thymidine, a nucleoside. It has shown effectiveness against herpes simplex virus Herpes simplex virus 1 and 2 (HSV-1 and HSV-2), also known by their taxonomical names ''Human a ...

is an antiviral drug. Telbivudine (β-L-2'-deoxythymidine, LdT) is the unmodified "unnatural" L-

enantiomer In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical ant ...

of thymidine that was used in the treatment of chronic

hepatitis B Hepatitis B is an infectious disease caused by the '' Hepatitis B virus'' (HBV) that affects the liver; it is a type of viral hepatitis. It can cause both acute and chronic infection. Many people have no symptoms during an initial infection. F ...

Thymidine imbalance induces mutation and recombination

During growth of bacteriophage T4, an excess of thymidine availability increases

mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, m ...

.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 A deficiency of thymidine during growth also increases mutation. A thymidylate auxotroph of the diploid yeast ''Saccharomyces cerevisiae'' was grown under conditions in which thymidyate levels varied from excess to depletion.Eckardt F, Kunz BA, Haynes RH. Variation of mutation and recombination frequencies over a range of thymidylate concentrations in a diploid thymidylate auxotroph. Curr Genet. 1983 Sep;7(5):399-402. doi: 10.1007/BF00445881. PMID: 24173422 High levels of thymidylate were observed to be mutagenic and recombinogenic, whereas starvation for thymidylate was recombinogenic but only slightly mutagenic.

References

External links

* http://money.cnn.com/magazines/fortune/fortune_archive/1990/11/05/74308/index.htm {{Nucleobases, nucleosides, and nucleotides Nucleosides Pyrimidinediones Hydroxymethyl compounds