1. Gram + & Gram – Bacteria THE BACTERIAL CELL WALL

2.  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 THE CELL WALL

3.  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 COMPOSITION & CHARACTERISTICS

4.  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 PEPTIDOGLYCAN STRUCTURE Tetrapeptide chain Peptide bridge Peptidoglycan Tetrapeptide chain

5.  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 POSITIVE (+) CELL WALL

6. GRAM + CELL WALL What do the green spheres represent? What do the blue spheres represent?

7.  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 http://faculty.ccbcmd.edu/courses/bio141/lecguide/unit1/pr ostruct/penres_fl.html GRAM (+) AND ANTIBIOTICS

8.  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 NEGATIVE (-) CELL WALL

9.  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 (–) CELL WALL

10.  Analyze the Gram – bacterial structure  Why would Gram – bacteria be more resistant to antibiotics? GRAM (-) AND ANTIBIOTICS

11.  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

12. GRAM STAIN LAB TEST