•
Outer boundary of the cell; one of the most important
parts of a Procaryotic cell
•
Most bacteria
have strong walls that give them shape and protect them from osmotic lysis (Exception-
mycoplasmas and some Archaea)
•
Wall shape and strength is primarily due to peptidoglycan
•
The cell walls of many pathogens contribute to their pathogenicity
•
The wall can
protect a cell from toxic substances and is the site of action of
several antibiotics
Peptidoglycan or Murein
•
polymer composed of identical subunits
•
alternating sugar derivatives-
•
N-acetylglucosamine (NAG) &
N-acetylmuramic acid (NAM)
•
Connected to the carboxyl group of N-acetylmuramic
acid is a peptide chain of 4 alternating D- and L-amino acids (D-glutamic acid,
L/D-alanine, diaminopimelic acid (not found in proteins) etc. (L-lysine, in
some)
•
The presence of D-amino acids protects against attack
by most peptidases
•
Chains of linked peptidoglycan subunits are joined by
cross- links between the peptides
•
Cross-linking results in a dense, interconnected
network of peptidoglycan
•
strong enough - retain the shape and integrity
•
elastic and stretchable
•
porous, for molecules to penetrate
Gram-Positive Cell Walls
•
Thick, homogeneous cell wall of gram-positive bacteria
composed primarily of peptidoglycan
•
Contain large amounts of teichoic acids (polymers
of glycerol or ribitol joined by phosphate groups)
• Teichoic acids extend to the surface of the peptidoglycan-negatively charged- give the gram-positive cell wall its negative charge.
• Important in maintaining the structure of the wall.
• Teichoic acids - not present in gram-negative bacteria.
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