Cell wall structure
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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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