Nucleosome structure: Difference between revisions

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New page: ==La unidad básica de la cromatina: el nucleosoma== ---- <Structure load='1aoi' size='600' frame='true' align='right' caption='Nucleosoma' scene='60/602771/Proteinas/5' /> <big><big>El '...
 
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==La unidad básica de la cromatina: el nucleosoma==
[[es:Nucleosome structure (Spanish)]]
----
<Structure load='1aoi' size='450' frame='true' align='right' caption='Nucleosome [[1aoi]]' scene='60/602771/Nucleosoma/3'/>
<big><big>'''Nucleosomes''' are the basic building blocks of '''chromatin fibers'''. A nucleosome consists of a core containing '''an octamer of histone proteins''' and a '''DNA''' molecule 146 bp long  wound around this core in two complete turns.
The <scene name='60/602771/Proteinas/5'>histone protein octamer</scene>  includes four types of proteins: <scene name='60/602771/Histonah2a/1'>H2A</scene>, <scene name='60/602771/Histonah2b/1'>H2B</scene>, <scene name='60/602771/Histonah3/1'>H3</scene> and <scene name='60/602771/Histonah4/1'>H4</scene>. Histone proteins are organized in dimers so:


----
*Two H3-H4 dimers
<Structure load='1aoi' size='600' frame='true' align='right' caption='Nucleosoma' scene='60/602771/Proteinas/5' />
**<scene name='60/602771/Dimeroh3h4-1/1'>H3-H4 dimer (1)</scene>
<big><big>El '''nucleosoma''' es la estructura básica de la '''fibra de cromatina'''. Un nucleosoma está constituido por un '''octámero de proteínas histónicas''' en su parte central y una doble hélice de '''DNA''' de 146 pares de bases de longitud que da dos vueltas casi completas alrededor de dicho octámero. En el recuadro de la derecha se puede apreciar el octámero de histonas.
**<scene name='60/602771/Dimeroh3h4-2/1'>H3-H4 dimer (2)</scene>
El octámero de histonas está formado por cuatro tipos de histonas diferentes: <scene name='60/602771/Histonah2a/1'>H2A</scene>, <scene name='60/602771/Histonah2b/1'>H2B</scene>, <scene name='60/602771/Histonah3/1'>H3</scene> y <scene name='60/602771/Histonah4/1'>H4</scene> (hay dos moléculas de cada tipo). Los diferentes tipos de histonas están dispuestos en dímeros del siguiente modo:
*Two H2A-H2B dimers
**<scene name='60/602771/Dimeroh2a-h2b-1/1'>H2A-H2B dimer (1)</scene>
**<scene name='60/602771/Dimeroh2a-h2b-2/1'>H2A-H2B dimer (2)</scene>
 
*<scene name='60/602771/Octamero/1'>Whole octamer</scene>
*<scene name='60/602771/Nucleosoma/3'>DNA</scene> molecule wound in <scene name='60/602771/Nucleosoma/4'>two complete turns</scene> around octamer. Some <scene name='60/602771/Nucleosoma/5'>manganese ions</scene> complete the whole structure.
 
The main secondary structure in <scene name='60/602771/Octamero/2'>histones</scene> is <scene name='60/602771/Secondarystructure/1'>alpha helices</scene>.


*Dos dímeros H3-H4
If we highlight the different types of amino acid residues on the <scene name='60/602771/Esqueleto/1'>protein backbone</scene> we can see that <scene name='60/602771/Residuosnegativos/1'>negatively charged residues</scene> and <scene name='60/602771/Residuospositivos/1'>positively charged residues</scene> are arranged so positively  charged residues are in <scene name='60/602771/Periferia/1'>peripheral positions</scene>, where they can form ionic interactions ([[salt bridges]]) with <scene name='60/602771/Interacciones/1'>phosphate groups on the DNA molecule</scene>. This distribution of electric charges stabilizes the whole structure.
**<scene name='60/602771/Dimeroh3h4-1/1'>Dímero H3-H4 (1)</scene>
**<scene name='60/602771/Dimeroh3h4-2/1'>Dímero H3-H4 (2)</scene>
*Dos dímeros H2A-H2B
**<scene name='60/602771/Dimeroh2a-h2b-1/1'>Dímero H2A-H2B (1)</scene>
**<scene name='60/602771/Dimeroh2a-h2b-2/1'>Dímero H2A-H2B (2)</scene>


Veamos ahora el <scene name='60/602771/Octamero/1'>octámero</scene> completo.
<small>
La doble cadena polinucleotídica de <scene name='60/602771/Nucleosoma/3'>DNA</scene> se dispone dando <scene name='60/602771/Nucleosoma/4'>dos vueltas casi completas</scene> alrededor del octámero de histonas.
==See Also==
*[[Nucleosome structure (Spanish)]]
*[[Nucleosomes]]
*[[User:Eric Martz/Nucleosomes]]


</StructureSection>
== References ==
== References ==
<references/>
<references/>
This page is based on [[1aoi]] file from Proteopedia.
[[1aoi]] is a 10 chain structure with sequence from [http://en.wikipedia.org/wiki/Xenopus_laevis Xenopus laevis]. The July 2000 RCSB PDB [http://pdb.rcsb.org/pdb/static.do?p=education_discussion/molecule_of_the_month/index.html Molecule of the Month] feature on ''Nucleosome''  by David S. Goodsell is [http://dx.doi.org/10.2210/rcsb_pdb/mom_2000_7 10.2210/rcsb_pdb/mom_2000_7]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1AOI OCA]. For a <b>guided tour on the structure components</b> use [http://oca.weizmann.ac.il/oca-docs/fgij/fg.htm?mol=1AOI FirstGlance].
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