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Transcript
THE BACTERIAL CELL WALL Gram + & Gram – Bacteria THE CELL WALL Is a complex, semi-rigid structure responsible for the shape of the cell as well as the size Surrounds the underlying, fragile plasma (cytoplasmic) membrane Protects it and the interior of the cell from adverse changes in the outside environment Major function is to prevent bacterial cells from rupturing Osmotic lysis Distinct Gram + and Gram - traits COMPOSITION & CHARACTERISTICS Composed of macromolecular network called peptidoglycan Peptidoglycan consists of repeating disaccharide attached by polypeptides to form a lattice that surrounds and protects the entire cell Disaccharide portion is made up of Alternating rows of 10-65 sugars to form a carbohydrate “backbone” Monosaccharides called N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) Adjacent rows are linked by polypeptides PEPTIDOGLYCAN STRUCTURE Covalently attached to each NAM is a tetrapeptide chain Tetrapeptide chains are linked by peptide cross -bridges The result is a 3-D meshwork held together by covalent bonds Tetrapeptide chain Peptidoglycan Peptide bridge Tetrapeptide chain GRAM POSITIVE (+) CELL WALL Many layers of peptidoglycan Thick layer (rigid structure) of peptidoglycan Thicker than Gram – cell wall Cell wall contains teichoic acids Help in: Attachment to surfaces Provides rigidity Helps in cell growth regulation Two types Lipoteichoic acid Wall teichoic acid Produce Exotoxins Stains Purple during Gram Stain Lab test Example: Streptococcus pyogenes (strep throat) GRAM + CELL WALL What do the green spheres represent? What do the blue spheres represent? GRAM (+) AND ANTIBIOTICS Analyze the cell wall of a Gram + bacteria What part would be attacked by antibiotics and why? What would this do to the cell. Explain http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit1/pr ostruct/penres_fl.html GRAM NEGATIVE (-) CELL WALL One or very few layers of peptidoglycan Thin layer (not as thick as gram +) Does NOT contain teichoic acids Has an outer membrane outside the peptidoglycan layer Consists of lipopolysaccharide (LPS), lipoproteins, phospholipids GRAM (–) CELL WALL The outer membrane has several specialized functions Its strong negative charge is an important factor in evading phagocytosis Provides a barrier to certain antibiotics (for example penicillin), digestive enzymes, detergents Permeability of outer membrane due to porins which allow passage of large molecules across the outer membrane LPS (known as endotoxin) helps bacteria secrete toxins Endotoxins and Exotoxins Example: Escherichia coli (food poisoning) Stains Pink in Gram Stain Lab test GRAM (-) AND ANTIBIOTICS Analyze the Gram – bacterial structure Why would Gram – bacteria be more resistant to antibiotics? GRAM STAIN Dif ferences between Gram (+) and Gram ( -) Bacteria: Structural and functional differences between Gram -positive and Gram-negative cell walls can be used for identification and treatment of bacterial infections. Basis for Gram stain (gram-positive = purple; gram-negative = pink) GRAM STAIN LAB TEST