Lecture 7- cell walls

Bacterial Cell walls overview:

• Helps determine shape of cell

• Protects cell from osmotic lysis & toxins

• Maintains cell integrity

• Can contribute to pathogenicity

• Virulence factors

  • Adherence and colonization factors

  • invasins

  • Capsules and surface components

  • Endotoxins

  • Exotoxins

  • siderophores

  • transport of toxins

Differences between + and - cell walls are?

How gram positive cell walls have a bigger layer of peptidoglycan.

NAM stands for?

N-acetyl muramic acid

NAG stands for?

N-acetyl glucosamine

DAP stands for?

Diaminopimelic acid

importance of D-amino acids

Tetra peptide crosslinking

direct crosslinks and peptide interbridge.

peptidoglycan structure

disaccharides + tetrapeptides

transpeptidase?

How does penicillin inhibit cell wall synthesis?

Building walls...how are subunits transported across the plasma membrane?

In gram + cell walls there are?

• Peptidoglycan 50-90% of cell envelope (20-80 nm)

• Teichoic acid

• Lipoteichoic acid

• Periplasmic space: gap between plasma membrane
  & cell wall

• Few proteins within the space

  • Exoenzymes

  • Β-lactamases or penicillinases

  • Others remain attached to plasma membrane

• surface protein

Teichoic acid and Lipoteichoic acid

Gram negative cell wall- lipopolysaccharide

• Lipid A Stabilizes OM structure

• Contributes to bacterial attachment

• Permeability barrier to toxic compounds

• O-antigen provides self protection due to rapid response in O-chain
  composition

• Endotoxin is the lipid A portion of the LPS molecule

Gram negative cell walls:

• Outer membrane more permeable
  than plasma membrane

• Permeability: porin proteins

  • passage of small molecules

  • blocks larger molecules

  • some nonspecific, some highly specific

Braun’s lipoprotein

hypotonic solutions

lysis

hypertonic solution

plasmolysis

protoplasts:

complete loss of cell wall

mycoplasma?

contain sterols in plasma membrane, stolen from the host

Which are the wall-less bacteria?

Mycoplasma and protoplasts

archaeal cell wall characteristics?

• Lack peptidoglycan

• variety of chemical make-ups

• Thick S-layer most common

  • Glycoprotein or protein

  • + additional layers