Nucleoside 89095 225262920 2008-07-12T19:35:02Z Cacycle 83784 copyedit <!-- Here is a table of data; skip past it to edit the text. --> {| border="1" cellpadding="2" cellspacing="0" align="right" style="margin-left:1em" |- align="center" valign="bottom" ! Nitrogenous base ! Nucleoside ! Deoxynucleoside |- align="center" valign="" | [[Image:Adenine_chemical_structure.png|58px|Chemical structure of adenine]]<br/>[[Adenine]]<br/> | [[Image:A_chemical_structure.png|95px|Chemical structure of adenosine]]<br/>[[Adenosine]]<br/>A | [[Image:dA_chemical_structure.png|95px|Chemical structure of deoxyadenosine]]<br/>[[Deoxyadenosine]]<br/>dA |- align="center" valign="" | [[Image:Guanine_chemical_structure.png|86px|Chemical structure of guanine]]<br/>[[Guanine]]<br/> | [[Image:G_chemical_structure.png|123px|Chemical structure of guanosine]]<br/>[[Guanosine]]<br/>G | [[Image:dG_chemical_structure.png|123px|Chemical structure of deoxyguanosine]]<br/>[[Deoxyguanosine]]<br/>dG |- align="center" valign="" | [[Image:Thymine_chemical_structure.png|63px|Chemical structure of thymine]]<br/>[[Thymine]]<br/> | [[Image:T_chemical_structure.png|87px|Chemical structure of 5-methyluridine]]<br/>[[5-Methyluridine]]<br/>m<sup>5</sup>U | [[Image:dT_chemical_structure.png|87px|Chemical structure of thymidine]]<br/>[[Deoxythymidine]]<br/>dT |- align="center" valign="" | [[Image:Uracil_chemical_structure.png|51px|Chemical structure of uracil]]<br/>[[Uracil]]<br/> | [[Image:U_chemical_structure.png|87px|Chemical structure of uridine]]<br/>[[Uridine]]<br/>U | [[Image:dU_chemical_structure.png|87px|Chemical structure of deoxyuridine]]<br/>[[Deoxyuridine]]<br/>dU |- align="center" valign="" | [[Image:Cytosine_chemical_structure.png|51px|Chemical structure of cytosine]]<br/>[[Cytosine]]<br/> | [[Image:C_chemical_structure.png|87px|Chemical structure of cytidine]]<br/>[[Cytidine]]<br/>C | [[Image:dC_chemical_structure.png|87px|Chemical structure of deoxycytidine]]<br/>[[Deoxycytidine]]<br/>dC |- |} '''Nucleosides''' are [[glycosylamine]]s consisting of a [[nucleobase]] (often referred to simply ''base'') to a [[ribose]] or [[deoxyribose]] [[sugar]]. Examples of these include [[cytidine]], [[uridine]], [[adenosine]], [[guanosine]], [[thymidine]] and [[inosine]]. Nucleosides can be [[phosphorylation|phosphorylated]] by specific [[kinase]]s in the cell on the sugar's primary alcohol group (-CH<sub>2−</sub>OH), producing [[nucleotide]]s, which are the molecular building blocks of [[DNA]] and [[RNA]]. Nucleosides are produced as the second step in [[nucleic acid digestion]], whereby [[nucleotidase]]s break down ''[[nucleotide]]s'' (such as the [[thymine]] nucleotide) into ''nucleosides'' (such as [[thymidine]]) and phosphate. The nucleosides, in turn, are subsequently broken down: * in the [[lumen]] of the digestive system by [[nucleosidases]] into nucleobases and ribose deoxyribose) * inside the cell by [[nucleoside phosphorylase]]s into [[nitrogenous base]]s, and [[ribose-1-phosphate]] or [[deoxyribose-1-phosphate]]. Nucleosides can be produced by combining nucleobases with deoxyribose rings as well. In medicine several [[nucleoside analogues]] are used as antiviral or anticancer agents. The viral polymerase incorporates these compounds with non-canon bases. These compounds are activated in the cells by being converted into nucleotides, they are administered as nuclosides since charged nucleotides cannot easily cross cell membranes. In molecular biology several [[nucleic acid analogues|analogues]] of the sugar back bone exist. Due to the low stability of RNA, which is prone to hydrolysis, several more stable alternative nucleoside/nucleotide analogues are used which correctly bind to RNA. This is achieved by using a different backbone sugar. These analogues include [[LNA]], [[morpholino]], [[PNA]]. In sequencing [[dideoxynucleotides]] are used. These nucleotides possess a non-canon sugar, dideoxyribose which lacks 3' hydroxyl group (which accepts the phosphate) and therefore cannot bond with the next base, terminating the chain as DNA polymerases mistake it for a regular deoxyribonucleotide. [[Image:Nucleotides v2.png|thumb|500px|left|The structure elements of the nucleosides and the phosphate group bearing nucleotides]] <br style="clear: both;" /> == See also == * [[Nucleobase]] * [[Nucleotide]] * [[RNA]] * [[Adenosine triphosphate]] (ATP) * [[Nucleic acid analogues]] {{Nucleobases, nucleosides, and nucleotides}} {{biochem-stub}} [[Category:Nucleosides|*]] [[ca:Nucleòsid]] [[cs:Nukleosid]] [[da:Nukleosid]] [[de:Nukleoside]] [[el:Νουκλεοζίτης]] [[es:Nucleósido]] [[fr:Nucléoside]] [[gl:Nucleósido]] [[id:Nukleosida]] [[it:Nucleoside]] [[ka:ნუკლეოზიდი]] [[lt:Nukleozidas]] [[hu:Nukleozid]] [[nl:Nucleoside]] [[ja:ヌクレオシド]] [[oc:Nucleosid]] [[pl:Nukleozydy]] [[sq:Nukleozidi]] [[sk:Nukleozid]] [[fi:Nukleosidi]] [[sv:Nukleosid]] [[zh:核苷]]