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O periplasma pode chegar a supoñer o 40% do volume celular total nas bacterias Gram negativas, mentres que a "zona da parede interna" das Gram positivas 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> A composición da "zona da parede interna" non foi aínda claramente determinada.
ItA isclasificación worthdas notingbacterias thaten althoughGram thepositivas bacteriae arenegativas conventionallyatendendo dividedao intoseu twotipo mainde groups,tinguidura [[Gram-positive]]é andbastante [[Gram-negative]],ambigua basedporque uponpode theirreferirse Gram-staina retentiontres property,aspectos thisdiferentes classification(resultado systemda istinguidura, ambiguousorganización asda itenvoltura can refers to three distinct aspects (staining resultcelular, cell-envelopegrupo organization, taxonomic grouptaxonómico), whichque donon notconcordan necessarilynecesariamente coalesceen forcertas someespecies bacterialde speciesbacterias. <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> Todas Allas bacterias [[Gram-positive bacteria]]positivas areestán boundedrodeadas bypor onlyunha asoa singlemembrana unitlipoproteica lipide membranexeralmente andconteñen theyunha generallygrosa containcapa a(de thick layer (20-80 nm) ofde peptidoglycan[[peptidoglicano]] responsibleresponsable forde retainingreter thea tinguidura de Gram-stain. AVarias numberespecies ofde otherbacterias bacteriaque whichteñen areunha boundedenvoltura bycunha asoa single membranemembrana, butpero whichque stainse tinguen como se fosen Gram-negative duenegativas todebido eitherá lackfalta ofde thecapa peptidoglycande layerpeptidoglicano (viz.,caso mycoplasmasdos [[micoplasma]]s) orou theirpola inabilitysúa toincapacidade retainde thereter a tinguidura de Gram-stain duepor tomor theirda cellcomposición da wallsúa compositionparede, alsomostran showtamén closeunha relationshipestreita torelación thecoas gram-positivebacterias bacteriaGram positivas. 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>
In diderm [[bacterium|bacteria]], the '''periplasm''' contains a thin [[cell wall]] composed of [[peptidoglycan]]. In addition, it includes solutes such as ions and proteins, which are involved in wide variety of functions ranging from nutrient binding, transport, folding, degradation, substrate hydrolysis, to [[peptidoglycan]] synthesis, [[electron transport]], and alteration of substances toxic to the cell ([[xenobiotic metabolism]]).<ref name="isbn0-07-295175-3">{{cite book |author=Klein, Donald W.; Prescott, Lansing M.; Harley, John |title=Microbiology |publisher=McGraw-Hill Higher Education |location=Boston |year=2005 |pages= |isbn=0-07-295175-3 |oclc= |doi=}}</ref> Importantly, the periplasm is devoided of ATP.
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