Lect7-KR - Bacterial cell walls PMB/MCB 112 September 15,...

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Bacterial cell walls PMB/MCB 112 September 15, 2010
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The bacterial cell wall
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Gram positive cell wall periplasm Teichoic acids are polymers of ribitol that give overall negative charge to the cell surface and bind Ca ++ and Mg ++ for eventual uptake
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Gram negative cell envelope PG is much thinner, OM is attached to PG via lipoproteins, OM contains porins for permeability, outer leaflet has LPS
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Structure of lipopolysaccharide (LPS) Lipid A = fatty acids linked to glucosamine phosphate via ester amine bond aka endotoxin, it can cause fever, diarrhea, and shock by activating the innate immune system Core polysaccharide contains hexoses, heptoses and ketodeoxyoctonate (KDO) O-specific polysaccharide (O-antigen) is species-specific and is made of hexoses in branched units that repeat. Involved in binding to plant/ animal host tissues and evading immune response. Protects cells from bile salts, hydrophobic antibiotics, complement activation Outer leaflet of OM Hydrophilic sugars form a dense layer covering the cell
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The peptidoglycan sacculus is one large macromolecule Glycan chains (dark blue) run around the circumference of the cell Peptide crosslinks (teal arrows) connect adjacent glycan strands
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Repeating unit of peptidoglycan NAG + NAM in β(1,4) linked chains Glycan chains attached by peptide cross-links Contains D-amino acids Diaminopimelic acid found only in Bacteria, has two amino groups, which allows peptide crosslinking
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Crosslinking peptides are different in different species More crosslinking yields greater rigidity
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Lect7-KR - Bacterial cell walls PMB/MCB 112 September 15,...

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