This MedLibrary.org supplementary page on Nucleoside is provided directly from the open source Wikipedia as a service to our readers. Please see the note below on authorship of this content, as well as the Wikipedia usage guidelines. To search for other content from our encyclopedia supplement, please use the form below:
Related Sponsors
| Nitrogenous base | Nucleoside | Deoxynucleoside |
|---|---|---|
 Adenine |
 Adenosine A |
 Deoxyadenosine dA |
 Guanine |
 Guanosine G |
 Deoxyguanosine dG |
 Thymine |
 5-Methyluridine m5U |
 Deoxythymidine dT |
 Uracil |
 Uridine U |
 Deoxyuridine dU |
 Cytosine |
 Cytidine C |
 Deoxycytidine dC |
Nucleosides are glycosylamines consisting of a nucleobase (often referred to simply base) bound to a ribose or deoxyribose sugar. Examples of these include cytidine, uridine, adenosine, guanosine, thymidine and inosine.
Nucleosides can be phosphorylated by specific kinases in the cell on the sugar's primary alcohol group (-CH2−OH), producing nucleotides, which are the molecular building blocks of DNA and RNA.
Nucleosides are produced as the second step in nucleic acid digestion, whereby nucleotidases break down nucleotides (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 phosphorylases into nitrogenous bases, 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 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.
See also
|
|||||||||||||||||||||||||||
 |
This biochemistry article is a stub. You can help Wikipedia by expanding it. |
Wikipedia content modification information:
- This page was last modified on 23 August 2008, at 15:19.
Wikipedia Authorship and Review
Wikipedia content provided here is not reviewed directly by MedLibrary.org. Wikipedia content is authored by an open community of volunteers and is not produced by or in any way affiliated with MedLibrary.org.
Wikipedia Usage Guidelines
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on "Nucleoside".
The URL for this specific entry is:
All Wikipedia text is available under the terms of the GNU Free Documentation License. (See Copyrights for details). Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc.