Microbiology 1010 – Lecture Notes
Role of the Cell Wall
Cell wall prevents cell expansion – protects against osmotic lysis
Protects against toxic substances – large hydrophobic molecules
o ex. detergents, antibiotics
Pathogenicity (when have a capsule)
o Helps evade host immune system
Helps bacterium stick to surfaces
Partly responsible for cell shape.
Why do we salt fish? It makes a hypertonic environment – which means the bacteria on the fish
dehydrate and shrink.
Species of Bacteria separated into two groups based on Gram stain
Gram-positives and gram-negatives have different cell wall structure (Figure 2.24)
Gram-negative cell wall
Two layers: LPS and peptidoglycan o
Gram-positive cell wall
One layer: peptidoglycan
Endospores – only from gram positive (but not all gram positive)
All gram neg. have lipid and sugar. Lipid is on the outer membrane and the sugar is then attached
to that. Together it is called LPS (lipopolysaccharide) = endotoxin.
LPS – is ‘o’ linked. It helps us to determine different features of bacteria.
It’s called an exotoxin = secreted to the outside
Endotoxin – is physically attached.
Once LPS is released from the dead cell, it can cause shock from the vassal dilation and can cause the
person to die. Which is why depending on the gram neg. bacteria infection, antibiotics won’t be given.
37 Microbiology 1010 – Lecture Notes
Periplasmic space = Area of the interior of the outer membrane and the exterior of the
In between these two membranes, there is the thin layer of peptidoglycan
38 Microbiology 1010 – Lecture Notes
Rigid layer that provides strength to cell wall
Polysaccharide composed of:
o N-acetylglucosamine (NAG) and N-acetylmuramic (NAM) acid
o Amino acids
o Lysine or diaminopimelic acid (DAP)
o Cross-linked differently in gram-negative bacteria and gram-positive bacteria
o Form glycan tetrapeptide
There is many different variations that are found within gram neg and positive bacteria.
NAM and NAG are the disaccharides when coupled together to make majority of the structure.
Creating a lattice.
The D form is unique to this case to the bacteria and few other exceptions.
The 5 glycine there is alternative amino acid threads to bridge the gap between the structure –
this glycine is specific for staphylococcus aureus.
39 Microbiology 1010 – Lecture Notes
Betta (1,4)Is what joins the monosaccharides (covalent bond)
Lysozyme- Natural enzyme (found in tears sweat Sylvia) has the acidity to destroy the linear
chains. Tetra peptide that makes the chain strong.
NAM and NAG is always consistent.
More than 100 different PG structures identified
Vary in peptide cros