Organization & Structure II

Organization & Structure II - The Cell Wall of...

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The Cell Wall of Prokaryotes
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Quiz The cytoplasmic membrane could best be described as a. an impermeable barrier b. a passive conduit for intracellular transport c. selectively permeable d. slightly permeable to water but impermeable to metabolic solutes
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The Cell Wall of Prokaryotes The Gram-Negative Outer Membrane A second lipid layer Contains polysaccharide and protein Lipid and polysaccharide linked to form lipopolysaccharides Often called the “lipopolysaccharide layer” or LPS.
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Chemistry of LPS Three Sections Lipid A Not a glycerol lipid Fatty acids connected to disaccharide of N-acetylglucosamine phosphate by ester amine linkages Endotoxin complex Core Polysaccharide Ketodeoxyoctonate (KDO) Sugars (heptoses, hexoses, GluNAc) in four- or five-members sequences O-polysaccharide 4 hexoses + one or more dideoxy sugars (e.g. abequose, paratose)
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Lipopolysaccharide of Gram-Negative Bacteria
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Porins Proteins in outer membrane Function as channels for hydrophilic, low mol. wt. substances Nonspecific porins : form water-filled channels which allow any substance to pass Specific porins : contains specific binding site for one or more substances
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Porin Structure and Function Usually contain three identical subunits Transmembrane proteins Form small holes ~ 1 nm Permeable to small molecules Impermeable to larger molecules Keep enzymes outside cytoplasmic membrane from diffusing away
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Porin Proteins
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Periplasm Space between the cytoplasmic membrane and inner surface of the outer membrane ~ 12-15 nm thick; gel-like consistency Periplasmic proteins : hydrolytic enzymes, binding proteins, chemoreceptors
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The Gram-Negative Cell Wall
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E. coli Cell Envelope
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New peptidoglycan must be added when a cell enlarges during division
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This note was uploaded on 10/09/2010 for the course MCB 3020C taught by Professor Safranek during the Summer '10 term at University of Central Florida.

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Organization & Structure II - The Cell Wall of...

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