Gram Negative Walls Flashcards
What are the functions of the Prokaryotic cell wall?
- defines cell structure
- protects against osmotic lysis
- contributes to pathogenesis often therefore it is the site of many antibiotics
what type of bacteria has an advantage to many antibiotics
Mycoplasma bacteria because they do not have a cell wall. Same with eukaryotes
What is the composition of Gram positive layers
- PM plus a thick electron dense thick layer
- thick peptidoglycan layer
- has techoic acids
What is the composition of Gram negative layers
- PM
- thin peptidoglycan layer
- OM
True or false, Archaea have no cell walls
False they have diverse cell walls but they have NO PEPTIDOGLYCAN
What type of bacteria have sterols inside their cytoplasmic membrane?
Mycoplasma!! for stability since they lack cell walls. They are osmotically sensitive.
what are the 4 reagents of a gram stain? What order are they applied?
1) Primary stain - crystal violet
2) mordant - Grams iodine
3) decolourize reagent - acetone
4) counter-stain - Safranin
What colour do Gram positive and negative bacteria appear As?
(+) - violet
(-) - pink
E. Coli and Staph epidermidis are examples of +/-?
E. Coli is gram negative
Staph is gram positive
Extending from the peptidoglycan layer, what 3 proteins are seen in gram negative bacteria?
1) LPS (lipopolysaccharides) extend at very surface
2) Porins exist in the phospholipid OM
3) Brauns Lipoprotein which connects Peptidoglycan with OM
What is the purpose of the OM
- keeps periplasm inside cell
- has many toxic properties
- chemically distinct from PM
- permeable to Di-saccharides due to PORINS
What protein is responsible for the OM’s toxic behaviour? Where is it located?
Lipopolysaccharides!! They are only found on GRAM NEGATIVES they are unsymmetrically on the outer leaflet of the OM and cover 40% of cell surface 3-9% dry weight of cell!! very toxic
What is Endotoxin?
term doctors use for LPS
What are a few illnesses known to be caused by endotoxins?
Diarrhea
fibrinolysis
Pyrogenic (induces fever)
If someone were infected by a Gram positive endotoxin what may be the symptoms
none, gram positives do not have LPS
What are the components of LPS?
Lipid A, a Core, and O-antigenic side chain
True or false, cells that cannot make the base structure of LPS are not viable
True, If a cell cannot make Lipid A and the first few structures of the core called KDO then they will not survive!
Explain Lipid A
- 6-7 fatty acids connected to a phosphorylated glucosamine
- the reason why LPS is toxic
- Fatty acids are either directly linked to GA or ether linked to 3’OH fatty acids on GA already
Explain LPS’s Core
connected to Lipid A at 6th position of glucosamine. built with 8-10 unusual sugars, often phosphorylated and branched.
what sugars are in the LPS core? What sugar connects the core to Lipid A?
KDO, heptose, and other normal ones
KDO IS RESPONSIBLE FOR CONNECTION TO LIPID A
Explain LPS’s O-antigenic side chain
- made up of hydrophilic sugars and amino acids in groups of 3-5 which are polymerized 30 ish times
- this is what your body develops antibodies too
Explain LPS synthesis
The entire protein is made inside the cytoplasm and has to be transported together
the formation is strictly sequential from lipid A
e.g the side chain cannot be added at all until the core is done.
side chain is added in repeating units of 3-5 NEVER AS SINGLE SUGARS
how are core sugars added vs antigenic sugars?
core - one at a time
antigenic - in 3-5 subunits
Explain Brauns Lipoprotein
- one of the most abundant proteins in the cell
- connects OM to PG
- Has a N-terminus which is cysteine group on OM
- Has a C-terminus which connects a lysine group to the DAP part of PG
Explain Outer Membrane proteins? what is the common one? what are their properties?
- usually rare, bacteria only have a few
- usually acidic
- usually form a trimer and act as a porin to allow hydrophilic substates past the OM
- non covalently associated with PG
- On the surface of cell and often act as bacteriophage receptors too
T or f, Gram negative and positive cells have OMP’s
NO, how can positive have them without an OM??
What is the one OMP that has a structural role?
OMP-A
what are the OMP’s that are non specific porins?
OMP-F and OMP-C
What do PhoE, LamB, Tsx, and TonA allow in?
PhoE - phosphate
LamB - lamba recpetor, Maltose
Tsx - T6 receptor, lets in nucleosides
TonA - T1 receptor, lets in ferrichrome
True or false, the periplasm is a large
false, it appears large in microscope but its not. Its small due to pressure and Brauns lipoprotein
