2-4: Bacterial Outer Membranes & More Flashcards
What gram status has an outer membrane
Gram negative
What important molecule makes up the outer membrane
Lipopolysaccharide
How do the compositions of the outer and inner OM leaflets vary
Outer = Some phospholipid, mostly LPS
Inner = phospholipid
What are the three parts of LPS
- Lipid A
- Core polysaccharide
- O-specific polysaccharide
What is Lipid A
base of LPS, anchored into OM by hydrophobic tails. Phosphates with negative charge
How is Lipid A related to the immune system
it is an endotoxin that can be sensed by the immune system, can lead to unchecked immune response (septic shock) if detected in blood stream
What is the O-specific polysaccharide
Diverse sugar subunits, variable
The OM is anchored to the CW via…
Braun’s lipoprotein
How does braun’s lipoprotein anchor the OM and CW
Lipid is anchored in OM, covalently attached to peptidoglycan of CW
Is the membrane permeable?
Impermeable to large molecules (proteins)
Permeable to small molecules
How is the OM permeable
Porins (protein channels allow entrance/exit of small molecules)
Are porins specific
Either or
What are the functions of the OM
Mechanical strength
barrier (less than CM) but soaks up/blocks access
Important for antibiotic sensitivity
Protects cell wall
Enables periplasmic space
The space between the OM and the CM is the…
In what gram state…
Periplasm, negative
Is there a periplasm in gram positive cells
Kinda (space between CM and CW) but is small, function not clear
What are the functions of the periplasm
Buffer btw environmental & cell
Break down macromolecules, take up as nutrients
High affinity binding proteins for nutrients
Detoxify harmful
Protein folding
How does the periplasm aid in protein folding
Disulfide bond formation
What is the S-layer
Rigid/permeable monolayer of of protein or glycoprotein
Outermost layer
Function of the S-layer
Protective layer (from bacteriophages, host defenses)
Provide periplasmic space
What are capsules and slime layers, what’s the difference
Coats of polysaccharides around cell surface
Capsule = organized into matrix, attached to the cell
Slime layers = loosely attached, less organized
Function of capsules/slime layers?
Adhering to surfaces, protection from host immune cells, protection from water loss
Protein filaments that extend from surface of the cell…
Pili
Function of conjugative pili?
Conjugation (transfer of genetic material between bacteria via pilus bridge)
Pilus that mediates attachment =
Fimbria
