Outer membrane polymers

Fig. 19. Twin-orifice spinnerette design used in solution-spinning of hoUow-fiber membranes. Polymer solution is forced through the outer orifice, while...

Below the outer membrane is a filter, usually composed of an anionic polymer, e.g. based on salicylate. Its precise composition and dimensions (thickness, pore size, amount and type of plasticizer, fillers, etc.) are optimized in order to tailor the diffusion rates of material crossing the filter from the analyte solution toward the working electrode of the sensor. Ideally, some uncharged molecules, such as H2O2, will traverse the filter so fast that, in effect, the filter is invisible to... 

Bacterial cells share certain common structural features, but also show group-specific specializations (Fig. 1-6). E. coli is a usually harmless inhabitant of the human intestinal tract. The E. coli cell is about 2 prri long and a little less than 1 prri in diameter. It has a protective outer membrane and an inner plasma membrane that encloses the cytoplasm and the nucleoid. Between the inner and outer membranes is a thin but strong layer of polymers called peptidoglycans, which gives the cell its shape and rigidity. The plasma membrane and the... 

In bacterial lipopolysaccharides, O-specific chains composed of repeating, or modified repeating, units are linked to a unique oligosaccharide sequence of the core region which is connected to a lipid A fragment serving as a hydrophobic anchor embedded in the bacterial outer-membrane. Biosynthesis of O-specific chains was found to occur independently on formation of other structural fragments of the lipopolysaccharide molecule. Both block and monomeric mechanisms were demonstrated for the biosynthesis of these polymers. 

Local delivery of bevacizumab at the vessel wall can be performed by dedicated stents coated with PC. The PC polymer mimics the chemical structure of the PC headgroup, which makes up 90% of phospholipids in the outer membrane of a red blood cell. PC has been shown to decrease protein absorption and platelet adhesion thereby we can expect that the PC coating reduces the thrombus formation of the stainless steel stent, allowing the prevention of subacute thrombosis. Both in vitro and in vivo researches have demonstrated that PC-based polymers are effective in improving the biocompatibility of inert materials (60-62). 

Cell envelopes of archaea diifer distinctly from those of bacteria and show remarkable structural and chemical diversity. Murein, the typical sacculus-forming polymer of bacteria, and lipopolysaccharide-containing outer membranes, characteristic of gramnegative bacteria, are not found in archaea. Crystalline surface layers (S-layers) are common in both prokaryotic domains and they consist of protein or glycoprotein subunits (Table 1). However, S-layers in archaea have a form-stabilizing function especially when they are the only envelope layer outside the cytoplasmic membrane, while in bacteria S-layers have no distinct form-stabilizing function. 

Structure similar to that of eukaryotes and a thick, bagshaped cell wall. The cell wall, about 25 nm wide, consists of peptidoglycans (Figure 11-14) and polyol phosphate polymers known as teichoic acids. Gram-negative bacteria (e.g., Escherichia coli and Salmonella typhimurium) do not contain teichoic acids but have an outer membrane system external to the plasma membrane and the peptidoglycan. The constituents of this second outer... 

Two proteins, FimC and FimB, are involved in the biogenesis of type 1 fimbriae, without being part of the final structure. The former acts as a periplasmic chaperon that stabilizes fimbria subunits in the periplasm through the formation of distinct complexes. The subunit-chaperon complexes are targeted to FimB, an outer membrane protein, which organizes their ordered secretion into an extracellular polymer [42]. Chaperons are also required for the assembly of other types of fimbriae, as well as of non-fimbrial lectins [43-45]. 

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