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Nucleosides are
glycosylamine 120px, Cyclic hemiaminal ether bond derived from an aldehyde Glycosylamines are a class of biochemical compounds consisting of a Glycosyl, glycosyl group attached to an amine, amino group, -NR2. They are also known as N-glycosides,. as they are a ty ...
s that can be thought of as
nucleotide Nucleotides are organic molecules , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, ...

nucleotide
s without a
phosphate group In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of atoms ...

phosphate group
. A nucleoside consists simply of a
nucleobase 230px, Pyrimidine nucleobases are simple ring molecules. Nucleobases, also known as ''nitrogenous bases'' or often simply ''bases'', are nitrogen-containing biological compounds that form nucleosides Nucleosides are glycosylamines that can be ...
(also termed a nitrogenous base) and a five-carbon sugar (
ribose Ribose is a simple sugar and carbohydrate with molecular formula C5H10O5 and the linear-form composition H−(C=O)−(CHOH)4−H. The naturally-occurring form, , is a component of the ribonucleotides from which RNA is built, and so this compoun ...

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 An anomer is a type of geometric variation found at certain atoms in carbohydrate is a disaccharide found in animal milk. It consists of a molecule of D-galactose and a molecule of D-glucose bonded by beta-1-4 glycosidic linkage. A carbohy ...
carbon is linked through a glycosidic bond to the N9 of a
purine Purine is a heterocyclic 125px, Pyridine, a heterocyclic compound A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different chemical element, elements as members of its ring(s). Heterocyclic chemi ...

purine
or the N1 of a
pyrimidine Pyrimidine is an aromatic In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts ...

pyrimidine
. Nucleotides are the molecular building-blocks of
DNA Deoxyribonucleic acid (; DNA) is a molecule A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically Electricity is the set of physical ...

DNA
and
RNA Ribonucleic acid (RNA) is a polymer A polymer (; Greek ''wikt:poly-, poly-'', "many" + ''wikt:-mer, -mer'', "part") is a Chemical substance, substance or material consisting of very large molecules, or macromolecules, composed of many Re ...

RNA
.


List of nucleosides and corresponding nucleobases

The reason for 2 symbols, shorter and longer, is that the shorter ones are better for contexts where explicit disambiguation is superfluous (because context disambiguates) and the longer ones are for contexts where explicit disambiguation is judged to be needed or wise. For example, when discussing long nucleobase sequences in genomes, the CATG symbol system is much preferable to the Cyt-Ade-Thy-Gua symbol system (see '' Nucleic acid sequence § Notation'' for examples), but in discussions where confusion is likelier, the unambiguous symbols can be used.


Sources

Nucleosides can be produced from nucleotides ''de novo'', particularly in the liver, but they are more abundantly supplied via ingestion and digestion of nucleic acids in the diet, whereby
nucleotidase A nucleotidase is a hydrolase, hydrolytic enzyme that catalyzes the hydrolysis of a nucleotide into a nucleoside and a phosphate. : A nucleotide + H2O = a nucleoside + phosphate For example, it converts adenosine monophosphate to adenosine, and guan ...
s break down ''
nucleotide Nucleotides are organic molecules , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenation, ...

nucleotide
s'' (such as the
thymidine monophosphate Thymidine monophosphate (TMP), also known as thymidylic acid (conjugate acid, conjugate base thymidylate), deoxythymidine monophosphate (dTMP), or deoxythymidylic acid (conjugate acid, conjugate base deoxythymidylate), is a nucleotide that is used ...
) into ''nucleosides'' (such as
thymidine Thymidine (deoxythymidine; other names deoxyribosylthymine, thymine deoxyriboside) is a pyrimidine Pyrimidine is an aromatic heterocyclic compound, heterocyclic organic compound similar to pyridine. One of the three diazines (six-membered heter ...
) and phosphate. The nucleosides, in turn, are subsequently broken down in the lumen of the digestive system by
nucleosidase Purine nucleoside phosphorylase (PNP) also known as PNPase and inosine phosphorylase is an enzyme that in humans is encoded by the ''NP'' gene. In enzymology, a purine-nucleoside phosphorylase () is an enzyme that catalysis, catalyzes the chemica ...
s into nucleobases and ribose or deoxyribose. In addition, nucleotides can be broken down inside the cell into
nitrogenous base Nucleobases, also known as ''nitrogenous bases'' or often simply ''bases'', are nitrogen-containing biological compounds that form nucleosides Nucleosides are glycosylamines that can be thought of as nucleotide Nucleotides are organic mo ...
s, and ribose-1-phosphate or deoxyribose-1-phosphate.


Use in medicine and technology

In medicine several
nucleoside analogue Nucleoside analogues are nucleoside Nucleosides are s that can be thought of as s without a . A nucleoside consists simply of a (also termed a nitrogenous base) and a five-carbon sugar ( or 2'-deoxyribose) whereas a nucleotide is compose ...
s 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 acid A locked nucleic acid (LNA), also known as bridged nucleic acid (BNA), and often referred to as inaccessible RNA, is a modified RNA nucleotide in which the ribose moiety is modified with an extra bridge connecting the 2' oxygen and 4' carbon. The ...
s (LNA),
morpholino A Morpholino, also known as a Morpholino oligomer and as a phosphorodiamidate Morpholino oligomer (PMO), is a type of oligomer In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compoun ...

morpholino
s and
peptide nucleic acid Image:PNA en.svg, Peptide nucleic acid (PNA) is an artificially synthesized polymer similar to DNA or RNA. Synthetic peptide nucleic acid oligomers have been used in recent years in molecular biology procedures, diagnostic assays, and antisense th ...
s (PNA). In sequencing, dideoxynucleotides are used. These nucleotides possess the non-canonical sugar dideoxyribose, which lacks 3' hydroxyl group (which accepts the phosphate). It therefore cannot bond with the next base and terminates the chain, as DNA polymerases cannot distinguish between it and a regular deoxyribonucleotide.


Prebiotic synthesis of ribonucleosides

In order to understand how
life Life is a characteristic that distinguishes physical entities A bubble of exhaled gas in water In common usage and classical mechanics, a physical object or physical body (or simply an object or body) is a collection of matter within a ...

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 The RNA world is a hypothetical stage in the evolutionary history of life The history of life on Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surfa ...
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 Purine is a heterocyclic 125px, Pyridine, a heterocyclic compound A heterocyclic compound or ring structure is a cyclic compound that has atoms of at least two different chemical element, elements as members of its ring(s). Heterocyclic chemi ...

purine
and
pyrimidine Pyrimidine is an aromatic In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts ...

pyrimidine
nucleotides, both of which are necessary for reliable information transfer, and thus Darwinian natural selection and
evolution Evolution is change in the heritable Heredity, also called inheritance or biological inheritance, is the passing on of Phenotypic trait, traits from parents to their offspring; either through asexual reproduction or sexual reproduction, ...

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. Becker S, Feldmann J, Wiedemann S, Okamura H, Schneider C, Iwan K, Crisp A, Rossa M, Amatov T, Carell T. Unified prebiotically plausible synthesis of pyrimidine and purine RNA ribonucleotides. Science. 2019 Oct 4;366(6461):76-82. doi: 10.1126/science.aax2747. PMID: 31604305.


See also

* Arabinosyl nucleosides *
Nucleobase Nucleobases, also known as ''nitrogenous bases'' or often simply ''bases'', are nitrogen-containing biological compounds that form nucleosides Nucleosides are glycosylamines that can be thought of as nucleotide Nucleotides are organic mo ...
* Salvage enzyme * Synthesis of nucleosides


References


External links

* {{Authority control DNA