Download The bacterial Cell Wall

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