Microbiology 1010 – Lecture Notes
LPS: The Outer Membrane (Continued…)
Periplasm: space located between cytoplasmic and outer membranes
o ~15 nm wide
o Contents have gel-like consistency
o Houses many proteins
Porins: channels for movement of hydrophilic low-molecular-weight substances (Fig. 2.29c)
The periplasm is between the inside the outer membrane and the outside of the plasma membrane
(including the peptidoglycan).
Outer membrane is none selective = generic protein channels and specific protein channels. Job to
just get materials into the periplasm.
The periplasm is very viscous because it has a lot of dissolved content within.
You are going to have chaperons protein that collects the molecule or nutrient of interest and delivers it
to the face of the plasma membrane at the expense of ATP can bring it into the cell.
3 polypeptide subunits – The pore is hydrophilic is relatively none selective and as long as you can
fit, you can go through into the periplasm.
Relationship of Cell Wall Structure to Gram stain
In Gram stain reaction, insoluble crystal violet-iodine (CV-I) complex forms inside cell
Complex is extracted by alcohol from gram-negative, not gram-positive bacteria
Gram-positive bacteria have thick cell walls consisting mainly of peptidoglycan
Becomes dehydrated during alcohol step so pores in wall close
Prevents CV-I complex from escaping
Gram-negative bacteria – alcohol penetrates OM
CV-I extracted from cell
o cells appear nearly invisible until counterstained with second dye (safarin)
44 Microbiology 1010 – Lecture Notes
The ability to form complex's inside the cell
Provides colour (gram positive) allows the crystal violet to stick within the pores of the peptidoglycan.
Archaeal Cell Walls
Typically no outer membrane
o Polysaccharide similar to peptidoglycan (Figure 2.30)
o Composed of N-acetylglucosamine and N-acetylalosaminuronic acid
Found in cell walls of certain methanogenic Archaea
Cell walls of some Archaea lack pseudomurein
Waxy outer layer – Makes it impenetrable from the stains so it has be stained with a carboyl fussion
These guys have to have a plasma membrane and can adjust to temperatures by adding saturated
to more saturated fatty acids to plasma membranes.
Do not all have pseudomurein
More a restraint linkage beta (1,3) than the other peptidoglycan.
Instead of tetra there is a tripeptide
45 Microbiology 1010 – Lecture Notes
2.12 Archaeal Cell Walls (Continued….)
o Most common cell wall type among Archaea
o Consist of protein or glycoprotein
o Paracrystalline structure
o Some Archaea have only S-layer (no other cell wall components)
o Most have additional cell wall elements
Highly ordered in the array of molecules – Para crystalline structure
Some archaea do not have additional cell wall structure or components
Summary of Archaeal Cell Walls
Variety of structures possible
Some closely resemble peptidoglycan
Others lack polysaccharide completely
Most Archaea contain some type of cell wall structure – functions to prevent osmotic
lysis and give shape
Because they lack peptidoglycan, Archaea are resistant to lysozyme and penicillin
Cytoplasm – material bounded by plasma membrane (PM)
Protoplast – PM and everything within
o Macromolecules – amino acids, nucleotides,
etc o Soluble proteins
o DNA and RNA (nucleoid)
Cytosol – is the fluid within the cytop