Espazo periplásmico: Diferenzas entre revisións

Contido eliminado Contido engadido
Miguelferig (conversa | contribucións)
Sen resumo de edición
Miguelferig (conversa | contribucións)
Sen resumo de edición
Liña 1:
{{entradución}}
[[Ficheiro:Gram negative cell wall.svg|miniatura|dereita|250px|[[Parede celular]] dunha bacteria [[Gram negativa]].]]
O '''espazo periplásmico''' ou '''periplasma''' é o espazo que rodea a dúas barreiras de permeabilidade selectiva na cuberta das bacterias, como son a [[membrana plasmática]] ou membrana interna e a membrana externa das paredes das bacterias [[Gram negativa]]s. Falando estritamente, as bacterias [[Gram positiva]]s non teñen un verdadeiro espazo periplásmico porque teñen só unha membrana biolóxica lipoproteica, a [[membrana plasmática]], pero poden ter unha rexión denominada "zona da parede interna" (IWZ, ''inner wall zone'') situada entre a membrana plasmática e a [[parede celuklar5celular]]+ madura. <ref name="Matias & Beveridge, 2005">, Matias, V. R., and T. J. Beveridge. 2005. Cryo-electron microscopy reveals native polymeric cell wall structure in Bacillus subtilis 168 and the existence of a periplasmic space. Mol. Microbiol. 56:240-251. {{doi|10.1111/j.1365-2958.2005.04535.x}}.</ref><ref name="Zuber et al, 2006">, Zuber B, Haenni M, Ribeiro T, Minnig K, Lopes F, Moreillon P, Dubochet J. 2006. Granular layer in the periplasmic space of Gram-positive bacteria and fine structures of Enterococcus gallinarum and [[Streptococcus gordonii]] septa revealed by cryo-electron microscopy of vitreous sections. J Bacteriol. 188:6652-6660. {{doi|10.1128/​JB.00391-06}}</ref>
TheO '''periplasm'''periplasma maypode constitutechegar upa tosupoñer o 40% ofdo thevolume celular total cellnas volumebacterias in [[Gram-negative]] speciesnegativas, whereasmentres theque '''IWZ'''a is"zona drasticallyda smallerparede ininterna" das [[Gram-positive]] speciespositivas é moitísimo menor. <ref name="isbn3-540-42608-6">{{cite book |author=Otto Holst; Guntram Seltmann |title=The Bacterial Cell Wall |publisher=Springer |location=Berlin |year= |pages= |isbn=3-540-42608-6 |oclc= |doi=}}</ref> CompositionA ofcomposición theda '''IWZ'''"zona hasda notparede interna" beennon asfoi yetaínda clearlyclaramente determineddeterminada.
 
It is worth noting that although the bacteria are conventionally divided into two main groups, [[Gram-positive]] and [[Gram-negative]], based upon their Gram-stain retention property, this classification system is ambiguous as it can refers to three distinct aspects (staining result, cell-envelope organization, taxonomic group), which do not necessarily coalesce for some bacterial species.<ref name="Guptab"> Gupta, R.S. (1998) Protein phylogenies and signature sequences: A reappraisal of evolutionary relationships among archaebacteria, eubacteria and eukaryotes. Microbiol. Mol. Biol. Rev. 62: 1435-1491.</ref><ref name="Guptad">Gupta, R.S.(2000) The natural evolutionary relationships among prokaryotes. Crit. Rev. Microbiol. 26: 111-131.</ref><ref name="Desvaux et al., 2009">, Desvaux M, Hébraud M, Talon R, Henderson IR. 2009. Secretion and subcellular localizations of bacterial proteins: a semantic awareness issue. Trends Microbiol. 17:139-145. {{doi|10.1016/j.tim.2009.01.004}}</ref><ref name="Sutcliffe, 2010">, Sutcliffe IC. 2010. A phylum level perspective on bacterial cell envelope architecture. Trends Microbiol. 18:464-470. {{doi|10.1016/j.tim.2010.06.005}}</ref> However, although Gram-staining response of bacteria is an empirical criterion, its basis lies in the marked differences in the ultrastructure and chemical composition of the two main kinds of prokaryotic cells that are found in nature. These two kinds of cells are distinguished from each other based upon the presence or absence of an outer lipid membrane, which is a more reliable and fundamental characteristic of the bacterial cells. <ref name="Guptab" /><ref name="Guptaa">Gupta, R. S. (1998). What are archaebacteria: life’s third domain or monoderm prokaryotes related to Gram-positive bacteria? A new proposal for the classification of prokaryotic organisms. Molecular Microbiology. 29(3):695-707.</ref> All [[Gram-positive bacteria]] are bounded by only a single unit lipid membrane and they generally contain a thick layer (20-80 nm) of peptidoglycan responsible for retaining the Gram-stain. A number of other bacteria which are bounded by a single membrane, but which stain Gram-negative due to either lack of the peptidoglycan layer (viz., mycoplasmas) or their inability to retain the Gram-stain due to their cell wall composition, also show close relationship to the gram-positive bacteria. For the bacterial (prokaryotic) cells that are bounded by a single cell membrane the term '''Mononderm Bacteria''' or '''Monoderm Prokaryotes''' has been proposed. <ref name="Guptab" /><ref name="Guptaa" /><ref name="Guptab" /> In contrast to Gram-positive bacteria, all archetypical Gram-negative bacteria, are bounded by both a cytoplasmic membrane as well as an outer cell membrane and they contain only a thin layer of peptidoglycan (2-3 nm) in between these two membranes. The presence of both inner and outer cell membranes forms and define the [[periplasmic space]] or periplasmic compartment. These bacterial cells with two membranes have been designated as '''Diderm Bacteria'''.<ref name="Guptab" /><ref name="Guptaa" /><ref name="Guptab" /> The distinction between the monoderm and diderm prokaryotes is also supported by [[conserved signature indels]] in a number of important proteins (viz. DnaK, GroEL). <ref name="Guptad" /><ref name="Guptaa" /><ref name="Guptab" /><ref name="Guptac">Gupta, R. S. (2011). Origin of diderm (Gram-negative) bacteria: antibiotic selection pressure rather than endosymbiosis likely led to the evolution of bacterial cells with two membranes. Antonie van Leeuwenhoek. 100:171-182.</ref>