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Cell wall structure. I. Function. A Prevent cell rupture due to osmotic pressure B Provides Shape C Anchors flagella. II. Clinically important. Site of antibiotic action B. Virulence factor that causes disease. III Components. A. Peptidoglycan B. Peptides and proteins

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i function
I. Function

A Prevent cell rupture due to osmotic pressure

B Provides Shape

C Anchors flagella

ii clinically important
II. Clinically important
  • Site of antibiotic action

B. Virulence factor that causes disease

iii components
III Components

A. Peptidoglycan

B. Peptides and proteins

C. Phospolipids

D. Polysaccharides

iv what is a peptidoglycan layer1
IV What is a Peptidoglycan Layer?

A rigid lattice structure made of long polymer of repeating disaccharide sugars that are bond together by polypeptide chains

  • Polymer of disaccharide sugar
    • Made of alternating N-acetylglucosamine (NAG) and N-acetylmurmic acid (NAM)
    • Form long rods that are refered to as the "carbohydrate backbone”
the peptidoglycan layer cont
The Peptidoglycan Layer (cont.)
  • The carbohydrate backbones are held in place laterally by peptide cross bridges
    • Peptide cross bridge binds NAG
  • The carbohydrate backbones are held together vertically by tetrapeptides
    • Tetrapeptides bind to NAM
gram positive cell walls
Gram Positive Cell Walls
  • Cell wall is made up of many peptidoglycan layers (very thick and rigid)
  • Contain teichoic acids
    • Lipoteichoic acids spans peptidoglycan layer and links to the plasma membrane.
    • Wall teichoic acid links to peptidoglycan layer.
  • Functions of teichoic acid
    • Movement of cations
    • Suport wall durring cell growth
    • Strong antigenic determinant
gram negative cell walls
Gram Negative Cell Walls
  • Outer membrane is unique in all of biology. Creates a periplasmic space.
    • Peptidoglycan layer inside the periplasmic space
    • Protein receptors that regulate chemotaxis.
gram negative cell walls cont
Gram Negative Cell Walls (cont.)

2. Outer membrane composed of

  • Phospholipid bilayer: Protects the cell against antibiotics and other chemicals which attack the peptidoglycan layer
  • Lipopolysaccharide layer:
    • O polysccharide (Strongist antigenic determinant).
    • Lipid A (endotoxin). Extremely toxic in minute amount
  • Porin proteins: Channel by which nutrients and waste pass through the cell wall.
  • Lipoproteins: Proteins that connect the outer membrane and the plasma membrane
gram stain
Gram Stain
  • Primary stain (crystal violet)
  • Wash
  • Mordant (Iodine)
  • Wash
  • Decolorizer (alchol/ acid wash)
  • Counter stain (Safranin)
  • Gram pos = primary stain sticks (crystal violet)
  • Gram neg. = Primary stain fails to bind. These cells are visualized by adding the counter stain (safranin)
movement of materials across membranes
Movement of Materials Across Membranes
  • Passive Processes
    • Simple diffusion: movement of molecules from areas of high concentration to area of low concentration.
    • Facilitated diffusion: Molecules combines with a plasma membrane protein called a transporter.
    • Osmosis: The movement of water across a selectively permeable membrane. High concentration to low concentration
movement of materials across membranes1
Movement of Materials Across Membranes
  • Active Transport: The cell uses energy (ATP) to move substance across the plasma membrane.
    • Moves substance from low concentration to high concentration
    • Depends on transporter protein
    • Group translocation: Substance is altered once it is across the membrane to make it impermeable to the membrane.
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