Complementariedade (bioloxía molecular): Diferenzas entre revisións

En [[bioloxía molecular]] a '''complementariedade''' é a propiedade compartida entre dúas [[secuencia de nucleótidos|secuencias de ácidos nucleicos]] que consiste en que cando ambos están alineados de forma [[Antiparalelo (bioquímica)|antiparalela]], as súas [[base nitroxenada|bases nitroxenadas]] dos seus [[nucleótido]]s en cada unha das posicións corresponden con outra base determinada, sempre a mesma, que se considera a súa '''complementaria'''. Por tanto, a complementariedade é unha '''complementariedade de bases'''. Dúas bases son complementarias se forman [[par de bases|pares de bases de Watson e Crick]], que poden establecer [[ponte de hidróxeno|pontes de hidróxeno]] estables entre elas. O grao de complementariedade entre dúas febras de [[ácido nucleico|ácidos nucleicos]] que se comparen é moi variable, desde total a nula, e mesmo ácidos nucleicos de distintas especies poden ter un grao de complementariedade, que lles permite hibridarse en certos tramos. As dúas febras do ADN son complementarias entre si, e un ARN acabado de [[transcrición xenética|transcribir]] é complementario coa febra [[sentido (bioloxía molecular)|antisentido]] ou molde do ADN a partir da cal se transcribiu.

 

[[File:Complementarity (DNA).png|thumb|right|250px|''Left:'' the [[nucleotide]] base pairs that can form in double-stranded [[DNA]]. Between A and T there are two hydrogen bonds, while there are three between C and G. ''Right:'' two complementary strands of DNA.]]

[[File:Primers RevComp.svg|thumb|Diagrammatic representation of the forward and reverse primers for a standard [[PCR]]. The reverse primer sequence is the reverse complement of the template DNA sequence.]]

A sequence that is equal to its reverse complement is said to be a [[palindromic sequence]].

 

In systematic biology it may be necessary to complement [[Nucleic acid notation#IUPAC notation|IUPAC codes]] that mean "any of the two" or "any of the three". The code R (any [[purine]]) can be complemented into Y (any [[pyrimidine]]) and M (amino) to K (keto). W (weak) and S (strong) are usually not swapped<ref>[http://code.izzid.com/2011/08/25/How-to-reverse-complement-a-DNA-sequence-in-perl.html Jeremiah Faith (2011)], conversion table</ref> while have been swapped in the past by some tools.<ref>[http://arep.med.harvard.edu/labgc/adnan/projects/Utilities/revcomp.html arep.med.harvard.edu] A tool page with the note about the applied W-S conversion patch.</ref> S and W is from "weak" and "strong", a number of the hydrogen bonds that a nucleotide uses to pair with its complementing partner. A partner uses the same number of the bonds to make a complementing pair.<ref name='rc'>[http://reverse-complement.com Reverse-complement tool] page with documented IUPAC code conversion, source code available.</ref>

 

Code that specifically excludes one of the three nucleotides can be complemented into code that excludes the complementing nucleotide. For instance, V (A,C or G - "not T") can be complemented into B (C, G or T - "not A").

 

By assigning suitable ([[Ambigram|ambigraphic]]) characters to complementary bases (i.e. guanine = ''b'', cytosine = ''q'', adenine = ''n'', and thymine = ''u''), it is possible to complement entire DNA sequences by simply rotating the text "upside down".<ref name=rozak1>{{cite journal |author=Rozak DA |title=The practical and pedagogical advantages of an ambigraphic nucleic acid notation |journal=Nucleosides Nucleotides Nucleic Acids |volume=25 |issue=7 |pages=807–13 |year=2006 |pmid=16898419 |doi=10.1080/15257770600726109 |url=http://www.tandfonline.com/doi/abs/10.1080/15257770600726109?url_ver=Z39.88-2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dpubmed}}</ref> For instance, with the previous alphabet, ''buqn'' (GTCA) would read as ''ubnq'' (TGAC, reverse complement) if turned upside down. This feature is enhanced by proposing custom fonts rather than ordinary ASCII or even Unicode characters.<ref name=rozak2>{{cite doi|10.2144/000112727}}</ref>