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 Nacetylglucosamine (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 bridges
a. Peptide cross bridge binds
NAG
3. The carbohydrate
backbones are held
together vertically by
tetrapeptides
a. Tetrapeptides bind to NAM
Gram Positive Cell Walls
1. Cell wall is made up of many
peptidoglycan layers (very
thick and rigid)
2. Contain teichoic acids
a. Lipoteichoic acids spans
peptidoglycan layer and links
to the plasma membrane.
b. Wall teichoic acid links to
peptidoglycan layer.
3. Functions of teichoic acid
a. Movement of cations
b. Suport wall durring cell
growth
c. 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. Wash
3. Mordant (Iodine)
4. Wash
5. 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.