2-4: Bacterial Outer Membranes & More Flashcards
Does gram positive or negative have an outer membrane
Gram negative
What important molecule makes up the outer membrane in Gram negative bacteria
Lipopolysaccharide
How do the compositions of the outer and inner OM leaflets vary
Outer = Liittle phospholipid, mostly LPS
Inner = phospholipid
What are the three parts of LPS
- Lipid A
- Core polysaccharide
- O-specific polysaccharide
What is Lipid A
contains 6 fatty acid tails and phosphates with negative charge. actual molecule varies depending on species
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
polysaccharaide made of diverse sugar subunits with a repeating combination of sugars, branched in different ways
how does the O-antigen vary between/within species?
usually conserved within the same STRAIN (eg. E. coli O157 serovar), but species can have different antigens
The OM is anchored to the CW via…
Braun’s lipoprotein
Braun’s lipoprotein is only found in gram positive or negative?
negative
How does braun’s lipoprotein anchor the OM and CW
Lipid is anchored in OM, protein is covalently attached to peptidoglycan of CW
Is the membrane permeable?
Impermeable to large molecules (proteins)
Permeable to small molecules
Why is the OM permeable
Contains porins (protein channels allow entrance/exit of small molecules)
How are porins regulated?
Depending on expression
What are the functions of the OM
Mechanical strength (due to ionic bonds between LPS and metal cations)
barrier (less than CM)
Important for antibiotic sensitivity
Protects cell wall (from lysozymes)
Enables periplasmic space
The space between the OM and the CM is the what?
In what gram bacteria?
Periplasm, negative
What are the functions of the periplasm
Buffer b/w environment & cell
Break down macromolecules, take up as nutrients
High affinity binding proteins for nutrients
Detoxify harmful compounds
Protein folding (disulfide bonds only form in oxidizing environments)
Describe the cell wall in Gram positive bacteria
Smaller space between the cell membrane and cell wall, importance less clear
The periplasm is the space between which two components?
Cytoplasmic membrane and cell wall - the space between outer membrane and cell wall is unknown
What is the S-layer
Rigid/permeable monolayer of of protein or glycoprotein
Always the outermost layer
Function of the S-layer
Protective layer (from bacteriophages, host defenses), Provide periplasmic space, prevent external proteins from accessing the OM
What are S layers most commonly found in?
Bacteria, but more commonly archaea
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
What are pilli?
Protein filaments that extend from surface of the cell
What type of bacteria produce pili?
Most bacteria, but particularly gram -
Function of conjugative pili?
Conjugation (transfer of genetic material between bacteria via pilus bridge)
What is Fimbria?
Pilus that mediates attachment
