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Cell wall structure. I. Function. APrevent cell rupture due to osmotic pressure BProvides Shape CAnchors flagella. II. Clinically important. Site of antibiotic action B. Virulence factor that causes disease. IIIComponents. A. Peptidoglycan B. Peptides and proteins - PowerPoint PPT Presentation
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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
A. Site of antibiotic action
B. Virulence factor that causes disease
III Components
A. Peptidoglycan
B. Peptides and proteins
C. Phospolipids
D. Polysaccharides
IV What is a Peptidoglycan Layer?
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
1. Polymer of disaccharide sugar a. Made of alternating N-
acetylglucosamine (NAG) and N-acetylmurmic acid (NAM)
b. Form long rods that are refered to as the "carbohydrate backbone”
The Peptidoglycan Layer (cont.)2. The carbohydrate
backbones are held in place laterally by peptide cross bridgesa. Peptide cross bridge binds
NAG
3. The carbohydrate backbones are held together vertically by tetrapeptidesa. Tetrapeptides bind to
NAM
Gram Positive Cell Walls1. Cell wall is made up of many
peptidoglycan layers (very thick and rigid)
2. Contain teichoic acidsa. Lipoteichoic acids spans
peptidoglycan layer and links to the plasma membrane.
b. Wall teichoic acid links to peptidoglycan layer.
3. Functions of teichoic acida. Movement of cationsb. Suport wall durring cell growthc. Strong antigenic determinant
Gram Negative Cell Walls
1. Outer membrane is unique in all of biology. Creates a periplasmic space.a. Peptidoglycan layer
inside the periplasmic space
b. Protein receptors that regulate chemotaxis.
Gram Negative Cell Walls (cont.)
2. Outer membrane composed of a. Phospholipid bilayer: Protects the cell against
antibiotics and other chemicals which attack the peptidoglycan layer
b. Lipopolysaccharide layer:1) O polysccharide (Strongist antigenic determinant).2) Lipid A (endotoxin). Extremely toxic in minute amount
c. Porin proteins: Channel by which nutrients and waste pass through the cell wall.
d. Lipoproteins: Proteins that connect the outer membrane and the plasma membrane
Gram Stain
1. Primary stain (crystal violet)
2. Wash3. Mordant (Iodine)4. Wash5. Decolorizer (alchol/
acid wash)6. 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
• 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 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.