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UNF MCB 2010C - Microbio Notes- Cell Walls

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Bacterial Cell Walls- Prokaryotes and Cell Wallso Outside plasma membrane o Provides shape and protects cell from osmotic breakdowno Exceptions: mycoplasma and certain archaea- Bacteria and Cell Wallso Peptidoglycan makes the wall rigid  Only bacteria have peptidoglycano Peptidoglycan structure Glycan chains of disaccharides held together by tetrapeptide chains Two sugars: NAG and NAM Layers of spirals Covalent bonds with peptide chainso Peptidoglycan Crosslinks  Contains D-isomers of amino acids and diaminopimelic acid (DAP) Direct connection or peptide interbridges  site of action of Penicillin!- attacks peptidoglycan crosslinks to weaken the cell wall - kills bacteria- Gram Positive vs Negative Cell Wallso Positive Inner plasma membrane Thick peptidoglycan- Around 30 sheets!- Permeable  Teichoic acids- Sugars attached to phosphate groups- Covalently attached to peptidoglycan via NAM - Gives peptidoglycan a negative charge - Triggers inflammationo Negative Outer and inner plasma membrane- Outer membrane contains lipids, lipoproteins, and LPS Thin peptidoglycan  Lipopolysaccharides (LPS)- Consists of O side chain (protection from host immune system), core polysaccharide (sugars that make cell surface negative), and Lipid A (embedded in membrane; acts as endotoxin)o Gram Staining  Difference occurs during decolorizer phase Thick peptidoglycan of gram-positive bacteria prevents crystal violet dye from leaking out  Alcohol/alcohol acetone creates holes in the outer membrane of gram-negative bacteria, causing crystal violet dye to leak out- Acid-Fast Bacteriao Atypical cell walls Structure resembles Gram-positive bacteria but does not stain consistently Waxy lipid outer layer  Contains mycolic acids - Long chain of fatty acids covalently bonded to peptidoglycan - Hydrophobic o Actinomycetes  Mycobacteria, diphtheriae, nocardia o Difficult to kill  Repels antibiotics, enzymes, and oxidizing chemicals - Acid-Fast Staino Step 1: Primary Dye  Carbofuchsin (pink) Uses heat to stain (steam bath)  No mordant Acid Fast BacteriaNon-Acid-Fast Bacteriao Step 2: Decolorizer  Acid alcohol Removes stain from non-acid-fast bacteria Acid Fast BacteriaNon-Acid-Fast Bacteriao Step 3: Counterstain Methylene blue Stains non-acid-fast bacteriaAcid Fast BacteriaNon-Acid-Fast


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