Nucleoside
Any of several glycosylamines comprising a nucleobase and a sugar molecule
Nucleosides are glycosylamines that can be thought of as nucleotides without a phosphate group. A nucleoside consists simply of a nucleobase (also termed a nitrogenous base) and a five-carbon sugar (ribose or 2'-deoxyribose) whereas a nucleotide is composed of a nucleobase, a five-carbon sugar, and one or more phosphate groups. In a nucleoside, the anomeric carbon is linked through a glycosidic bond to the N9 of a purine or the N1 of a pyrimidine. Nucleotides are the molecular building blocks of DNA and RNA.
01List of nucleosides and corresponding nucleobases
This list does not include modified nucleobases and the corresponding nucleosides
Each chemical has a short symbol, useful when the chemical family is clear from the context, and a longer symbol, if further disambiguation is needed. For example, long nucleobase sequences in genomes are usually described by CATG symbols, not Cyt-Ade-Thy-Gua (see Nucleic acid sequence § Notation).
| Nitrogenous base | Ribonucleoside | Deoxyribonucleoside |
|---|---|---|
adenine symbol A or Ade |
adenosine symbol A or Ado |
deoxyadenosine symbol dA or dAdo |
guanine symbol G or Gua |
guanosine symbol G or Guo |
deoxyguanosine symbol dG or dGuo |
thymine (5-methyluracil) symbol T or Thy |
5-methyluridine (ribothymidine) symbol m⁵U |
thymidine (deoxythymidine) symbol dT or dThd (dated: T or Thd) |
uracil symbol U or Ura |
uridine symbol U or Urd |
deoxyuridine symbol dU or dUrd |
cytosine symbol C or Cyt |
cytidine symbol C or Cyd |
deoxycytidine symbol dC or dCyd |
02Use in medicine and technology
In medicine several nucleoside analogues are used as antiviral or anticancer agents. The viral polymerase incorporates these compounds with non-canonical bases. These compounds are activated in the cells by being converted into nucleotides. They are administered as nucleosides since charged nucleotides cannot easily cross cell membranes.
In molecular biology, several analogues of the sugar backbone exist. Due to the low stability of RNA, which is prone to hydrolysis, several more stable alternative nucleoside/nucleotide analogues that correctly bind to RNA are used. This is achieved by using a different backbone sugar. These analogues include locked nucleic acids (LNA), morpholinos and peptide nucleic acids (PNA).
In sequencing, dideoxynucleotides are used. These nucleotides possess the non-canonical sugar dideoxyribose, which lacks 3' hydroxyl group (which accepts the phosphate). DNA polymerases cannot distinguish between these and regular deoxyribonucleotides, but when incorporated a dideoxynucleotide cannot bond with the next base and the chain is terminated.
03Prebiotic synthesis of ribonucleosides
In order to understand how life arose, knowledge is required of the chemical pathways that permit formation of the key building blocks of life under plausible prebiotic conditions. According to the RNA world hypothesis free-floating ribonucleosides and ribonucleotides were present in the primitive soup. Molecules as complex as RNA must have arisen from small molecules whose reactivity was governed by physico-chemical processes. RNA is composed of purine and pyrimidine nucleotides, both of which are necessary for reliable information transfer, and thus Darwinian natural selection and evolution. Nam et al. demonstrated the direct condensation of nucleobases with ribose to give ribonucleosides in aqueous microdroplets, a key step leading to RNA formation. Also, a plausible prebiotic process for synthesizing pyrimidine and purine ribonucleosides and ribonucleotides using wet-dry cycles was presented by Becker et al.
Sources and credits
This article is adapted from the Wikipedia article “Nucleoside”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.
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- Desoxyadenosin.svg by NEUROtiker, Public domain
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