THE BACTERIAL CELL WALL Gram Gram Bacteria THE

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 Tetrapeptide chain Peptide bridge

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/bio 141/lecguide/unit 1/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 Differences 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