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{{BioPsy}}
 
{{BioPsy}}
[[Image:DNAbasePairing2.png|thumb|470px|right|Chemical structure of base pair bonding. Thymine (T) bonds with adenine (A), and cytosine (C) bonds with guanine (G).]]
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[[File:AGCT RNA mini.png|thumb|Base pairing in RNA. Nucleobases in blue. Hydrogen bonds in red.]]
   
'''Nucleobases''' are the parts of [[RNA]] and [[DNA]] that may be involved in pairing (see also [[base pairs]]). These include [[cytosine]], [[guanine]], [[adenine]], [[thymine]] ([[DNA]]), [[uracil]] ([[RNA]]) and [[xanthine]] and [[hypoxanthine]] (mutated forms of guanine and adenine, respectively). These are abbreviated as C, G, A, T, U, X and HX respectively. They are usually simply called '''bases''' in [[genetics]]. Because A, G, C and T appear in the DNA, these molecules are called '''DNA-bases'''; A, G, C and U are called '''RNA-bases''', respectively.
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'''Nucleobases''' are nitrogen-containing biological compounds ([[nitrogenous base]]s) found within [[DNA|deoxyribonucleic acid]] (DNA), [[RNA|ribonucleic acid]] (RNA), [[nucleotides]], and [[nucleosides]]. Often simply called ''bases'' in [[genetics]], their ability to form [[base-pairs]] and to [[Stacking (chemistry)|stack]] upon one another lead directly to the [[helix|helical]] structure of DNA and RNA.
   
[[Hypoxanthine]] and [[xanthine]] are created through [[mutagen]] presence, through deamination (replacement of the amine-group with a hydroxyl-group). Hypoxanthine is produced from [[adenine]], xanthine from [[guanine]] and [[uracil]] from [[cytosine]].
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Use of the word ''base'' is historical, in reference to the chemical properties of nucleobases in [[Base (chemistry)|acid-base reactions]] within the test tube, and is not especially relevant or important for understanding most of their biological functions.
   
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The primary nucleobases are [[cytosine]] (DNA and RNA), [[guanine]] (DNA and RNA), [[adenine]] (DNA and RNA), [[thymine]] (DNA) and [[uracil]] (RNA), abbreviated as C, G, A, T, and U, respectively. Because A, G, C, and T appear in the DNA, these molecules are called DNA-bases; A, G, C, and U are called RNA-bases.
 
Uracil replaces thymine in RNA. These two bases are identical except that uracil lacks the 5' methyl group. Adenine and guanine belong to the double-ringed class of molecules called [[purine]]s (abbreviated as R). Cytosine, thymine, and uracil are all [[pyrimidine]]s (abbreviated as Y).
 
Uracil replaces thymine in RNA. These two bases are identical except that uracil lacks the 5' methyl group. Adenine and guanine belong to the double-ringed class of molecules called [[purine]]s (abbreviated as R). Cytosine, thymine, and uracil are all [[pyrimidine]]s (abbreviated as Y).
   
A base [[covalent]]ly bound to the 1' [[carbon]] of a [[ribose]] or [[deoxyribose]] is called a ''[[nucleoside]]'', and a nucleoside with one or more [[phosphate]] groups attached at the 5' carbon is called a ''[[nucleotide]]''.
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In normal spiral DNA the bases form [[DNA#Base pairing|pairs]] between the two strands: A with T and C with G. Purines pair with [[pyrimidines]] mainly for dimensional reasons - only this combination fits the constant width geometry of the DNA spiral. The A-T and C-G pairings are required to match the hydrogen bonds between the amine and carbonyl groups on the complementary bases.
   
==Structure==
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The compound formed when a nucleobase forms a [[glycosidic bond]] with the 1' [[anomeric]] [[carbon]] of a [[ribose]] or [[deoxyribose]] is called a ''[[nucleoside]]'', and a nucleoside with one or more [[phosphate]] groups attached at the 5' carbon is called a ''[[nucleotide]]''.
   
* The "skeleton" of adenine, guanin, hypoxanthine and xanthine is [[purine]], hence the name '''purine-bases'''.
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Apart from adenine (A), cytosine (C), guanine (G), thymine (T) and uracil (U), DNA and RNA also contain bases that have been modified after the nucleic acid chain has been formed. In DNA, the most common modified base is [[5-methylcytosine]] (m<sup>5</sup>C). In RNA, there are many modified bases, including those contained in the nucleosides [[pseudouridine]] (Ψ), [[dihydrouridine]] (D), [[inosine]] (I), and [[7-methylguanosine]] (m<sup>7</sup>G).<ref>[http://www.mun.ca/biology/desmid/brian/BIOL2060/BIOL2060-22/CB22.html BIOL2060: Translation<!-- Bot generated title -->]</ref><ref>[http://www.biogeo.uw.edu.pl/research/grupaC_en.html "Role of 5' mRNA and 5' U snRNA cap structures in regulation of gene expression"] - Research - Retrieved 13 December 2010.</ref>
* The "skeleton" of cytosine, uracil and thymine is [[pyrimidine]], hence '''pyrimidine-bases'''.
 
   
===Purines===
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[[Hypoxanthine]] and [[xanthine]] are two of the many bases created through [[mutagen]] presence, both of them through [[deamination]] (replacement of the amine-group with a carbonyl-group). Hypoxanthine is produced from adenine, xanthine from guanine.<ref>T Nguyen, D Brunson, C L Crespi, B W Penman, J S Wishnok, and S R Tannenbaum, [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=48797 DNA damage and mutation in human cells exposed to nitric oxide in vitro], Proc Natl Acad Sci U S A. 1992 April 1; 89(7): 3030–3034</ref> In similar manner, deamination of cytosine results in uracil.
   
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  +
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==Structure==
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* The "skeleton" of adenine and guanine is [[purine]], hence the name '''purine-bases'''.
  +
* The "skeleton" of cytosine, uracil, and thymine is [[pyrimidine]], hence '''pyrimidine-bases'''.
  +
  +
===Primary bases===
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These are incorporated into the growing chain during RNA and/or DNA synthesis.
 
{| border="1" cellpadding="2" cellspacing="0" align="none" style="margin-left:1em"
 
{| border="1" cellpadding="2" cellspacing="0" align="none" style="margin-left:1em"
 
|- align="center" valign="bottom"
 
|- align="center" valign="bottom"
! Nucleobase
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| '''Nucleobase'''|| [[File:Adenine.svg|58px|Chemical structure of adenine]]<br />[[Adenine]]|| [[File:Guanine chemical structure.png|86px|Chemical structure of guanine]]<br />[[Guanine]]|| [[File:Thymine chemical structure.png|63px|Chemical structure of thymine]]<br />[[Thymine]]|| [[File:Cytosine chemical structure.png|51px|Chemical structure of cytosine]]<br />[[Cytosine]]|| [[File:Uracil chemical structure.png|51px|Chemical structure of uracil]]<br />[[Uracil]]
! Nucleoside
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|- align="center" valign="bottom"
|- align="center" valign=""
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| '''Nucleoside'''|| [[File:Adenosin.svg|95px|Chemical structure of adenosine]]<br />[[Adenosine]]<br />A || [[File:G chemical structure.png|123px|Chemical structure of guanosine]]<br />[[Guanosine]]<br />G || [[File:T chemical structure.png|87px|Chemical structure of thymidine]]<br />[[Thymidine]]<br />T || [[File:C chemical structure.png|87px|Chemical structure of cytidine]]<br />[[Cytidine]]<br />C || [[File:U chemical structure.png|87px|Chemical structure of uridine]]<br />[[Uridine]]<br />U
| [[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
 
|- 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
 
|- align="center" valign=""
 
| [[Image:Hypoxanthine_chemical_structure.svg|70px|Chemical structure of hypoxanthine]]<br/>[[Hypoxanthine]]<br/>
 
| [[Image:HX_chemical_structure.svg|100px|Chemical structure of hypoxanthinosine]]<br/>[[Hypoxanthinosine]]<br/>HX
 
|- align="center" valign=""
 
| [[Image:Xanthine_chemical_structure.svg|70px|Chemical structure of xanthine]]<br/>[[Xanthine]]<br/>
 
| [[Image:X_chemical_structure.svg|100px|Chemical structure of xanthinosine]]<br/>[[Xanthinosine]]<br/>X
 
 
|-
 
|-
 
|}
 
|}
   
===Pyrimidines===
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===Modified purine bases===
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These are examples of modified adenosine or guanosine.
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{| border="1" cellpadding="2" cellspacing="0" align="none" style="margin-left:1em"
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|- align="center" valign="bottom"
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| '''Nucleobase'''|| [[File:Hypoxanthine.png|70px|Chemical structure of hypoxanthine]]<br />[[Hypoxanthine]]|| [[File:Xanthine oriented.png|80px|Chemical structure of xanthine]]<br />[[Xanthine]]|| [[File:7methylguanine.png|86px|Chemical structure of 7-methylguanine]]<br />[[7-Methylguanine]]
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|- align="center" valign="bottom"
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| '''Nucleoside'''|| [[File:Inosine.svg|95px|Chemical structure of inosine]]<br />[[Inosine]]<br />I || [[File:Xanthosine Haworth.png|105px|Chemical structure of xanthosine]]<br />[[Xanthosine]]<br />X || [[File:7-Methylguanosine.svg|118px|Chemical structure of 7-methylguanosine]]<br />[[7-Methylguanosine]]<br />m<sup>7</sup>G
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|-
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|}
   
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===Modified pyrimidine bases===
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These are examples of modified cytidine, thymidine or uridine.
 
{| border="1" cellpadding="2" cellspacing="0" align="none" style="margin-left:1em"
 
{| border="1" cellpadding="2" cellspacing="0" align="none" style="margin-left:1em"
 
|- align="center" valign="bottom"
 
|- align="center" valign="bottom"
! Nucleobase
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| '''Nucleobase'''|| [[File:Dihydrouracil.PNG|55px|Chemical structure of dihydrouracil]]<br />[[5,6-Dihydrouracil]]|| [[File:5-Methylcytosine.svg|70px|Chemical structure of 5-methylcytosine]]<br />[[5-Methylcytosine]]|| [[File:Hydroxymethylcytosine.png|60px|Chemical structure of 5-hydroxymethylcytosine]]<br />[[5-Hydroxymethylcytosine]]
! Nucleoside
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|- align="center" valign="bottom"
|- align="center" valign=""
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| '''Nucleoside'''|| [[File:Dihydrouridine.svg|87px|Chemical structure of dihydrouridine]]<br />[[Dihydrouridine]]<br />D || [[File:5-Methylcytidine.svg|87px|Chemical structure of 5-methylcytidine]]<br />[[5-Methylcytidine]]<br />m<sup>5</sup>C ||
| [[Image:Thymine_chemical_structure.png|63px|Chemical structure of thymine]]<br/>[[Thymine]]<br/>
 
| [[Image:T_chemical_structure.png|87px|Chemical structure of thymidine]]<br/>[[Thymidine]]<br/>T
 
|- 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
 
|- 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
 
 
|-
 
|-
 
|}
 
|}
   
== See also ==
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==Novel bases==
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{{main|Nucleic acid analogues}}
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A vast number of nucleobase analogues exist.
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The most common applications are used as fluorescent probes, either directly or indirectly, such as [[aminoallyl nucleotide]], which are used to label cRNA or cDNA in [[microarrays]].
  +
Several groups are working on alternative "extra" base pairs to extend the genetic code, such as [[isoguanine]] and [[isocytosine]] or the fluorescent 2-amino-6-(2-thienyl)purine and pyrrole-2-carbaldehyde.{{Citation needed|date=April 2012}}
   
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In medicine, several [[nucleoside analogues]] are used as anticancer and antiviral 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 nucleosides as charged nucleotides cannot easily cross cell membranes.{{Citation needed|date=April 2012}}
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== See also ==
 
* [[Nucleoside]]
 
* [[Nucleoside]]
 
* [[Nucleotide]]
 
* [[Nucleotide]]
 
* [[DNA]]
 
* [[DNA]]
 
* [[RNA]]
 
* [[RNA]]
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* [[Nucleic acid notation]]
   
 
==External links==
 
==External links==
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{{Nucleic acids}}
 
{{Nucleic acids}}
   
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[[Category:Biochemistry]]
 
[[Category:DNA]]
 
[[Category:DNA]]
 
[[Category:RNA]]
 
[[Category:RNA]]

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File:AGCT RNA mini.png

Nucleobases are nitrogen-containing biological compounds (nitrogenous bases) found within deoxyribonucleic acid (DNA), ribonucleic acid (RNA), nucleotides, and nucleosides. Often simply called bases in genetics, their ability to form base-pairs and to stack upon one another lead directly to the helical structure of DNA and RNA.

Use of the word base is historical, in reference to the chemical properties of nucleobases in acid-base reactions within the test tube, and is not especially relevant or important for understanding most of their biological functions.

The primary nucleobases are cytosine (DNA and RNA), guanine (DNA and RNA), adenine (DNA and RNA), thymine (DNA) and uracil (RNA), abbreviated as C, G, A, T, and U, respectively. Because A, G, C, and T appear in the DNA, these molecules are called DNA-bases; A, G, C, and U are called RNA-bases. Uracil replaces thymine in RNA. These two bases are identical except that uracil lacks the 5' methyl group. Adenine and guanine belong to the double-ringed class of molecules called purines (abbreviated as R). Cytosine, thymine, and uracil are all pyrimidines (abbreviated as Y).

In normal spiral DNA the bases form pairs between the two strands: A with T and C with G. Purines pair with pyrimidines mainly for dimensional reasons - only this combination fits the constant width geometry of the DNA spiral. The A-T and C-G pairings are required to match the hydrogen bonds between the amine and carbonyl groups on the complementary bases.

The compound formed when a nucleobase forms a glycosidic bond with the 1' anomeric carbon of a ribose or deoxyribose is called a nucleoside, and a nucleoside with one or more phosphate groups attached at the 5' carbon is called a nucleotide.

Apart from adenine (A), cytosine (C), guanine (G), thymine (T) and uracil (U), DNA and RNA also contain bases that have been modified after the nucleic acid chain has been formed. In DNA, the most common modified base is 5-methylcytosine (m5C). In RNA, there are many modified bases, including those contained in the nucleosides pseudouridine (Ψ), dihydrouridine (D), inosine (I), and 7-methylguanosine (m7G).[1][2]

Hypoxanthine and xanthine are two of the many bases created through mutagen presence, both of them through deamination (replacement of the amine-group with a carbonyl-group). Hypoxanthine is produced from adenine, xanthine from guanine.[3] In similar manner, deamination of cytosine results in uracil.


StructureEdit

  • The "skeleton" of adenine and guanine is purine, hence the name purine-bases.
  • The "skeleton" of cytosine, uracil, and thymine is pyrimidine, hence pyrimidine-bases.

Primary basesEdit

These are incorporated into the growing chain during RNA and/or DNA synthesis.

Nucleobase Chemical structure of adenine
Adenine
Guanine chemical structure
Guanine
Thymine chemical structure
Thymine
Cytosine chemical structure
Cytosine
Uracil chemical structure
Uracil
Nucleoside Chemical structure of adenosine
Adenosine
A
G chemical structure
Guanosine
G
T chemical structure
Thymidine
T
C chemical structure
Cytidine
C
U chemical structure
Uridine
U

Modified purine basesEdit

These are examples of modified adenosine or guanosine.

Nucleobase Chemical structure of hypoxanthine
Hypoxanthine
Chemical structure of xanthine
Xanthine
Chemical structure of 7-methylguanine
7-Methylguanine
Nucleoside Chemical structure of inosine
Inosine
I
Chemical structure of xanthosine
Xanthosine
X
Chemical structure of 7-methylguanosine
7-Methylguanosine
m7G

Modified pyrimidine basesEdit

These are examples of modified cytidine, thymidine or uridine.

Nucleobase Chemical structure of dihydrouracil
5,6-Dihydrouracil
Chemical structure of 5-methylcytosine
5-Methylcytosine
Chemical structure of 5-hydroxymethylcytosine
5-Hydroxymethylcytosine
Nucleoside Chemical structure of dihydrouridine
Dihydrouridine
D
Chemical structure of 5-methylcytidine
5-Methylcytidine
m5C

Novel basesEdit

Main article: Nucleic acid analogues

A vast number of nucleobase analogues exist. The most common applications are used as fluorescent probes, either directly or indirectly, such as aminoallyl nucleotide, which are used to label cRNA or cDNA in microarrays. Several groups are working on alternative "extra" base pairs to extend the genetic code, such as isoguanine and isocytosine or the fluorescent 2-amino-6-(2-thienyl)purine and pyrrole-2-carbaldehyde.[citation needed]

In medicine, several nucleoside analogues are used as anticancer and antiviral 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 nucleosides as charged nucleotides cannot easily cross cell membranes.[citation needed]

See also Edit

External linksEdit

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