Special bacterial structures Flashcards
1
Q
What is the lipopolysaccharide?
A
- Gram -ve fundamental
- Outermost lipid bilayer
2
Q
What are the functions of the LPS?
A
- Facilitate surface recognitions
- Virulence factors for pathogens
- Aid in mechanical strength of cell
3
Q
What are the components of the LPS?
A
3 main components: “OAP”
- O-specific side chain
- Core polysaccharide
- Lipid A
4
Q
What makes up the core polysaccharide?
A
- Constituents vary
- Solid + straight
- Salmonella has unusual sugars
5
Q
What makes up the O-specific side chain?
A
- Often branched 4-5 member sugar sequences
- Attach to core polysaccharide
- Are first point of contact with host cell
- Can change length to be rough or smooth to evade host immune system.
6
Q
What makes up the Lipid A?
A
- Fatty acids bonded via amine groups
- 2x Glucosamine residues
- Link to fatty acids + phosphate
- Solid + straight
7
Q
Why is LPS important?
A
- Toxic to host.
- Toxicity mainly from Lipid A
- Endotoxin = when free in host, can cause innate immune response
8
Q
How can we test for endotoxins?
A
2 tests:
- Limulus amaebocyte lysate (LAL)
- Rabbit pyrogen test
9
Q
What does each component bring to the overall function of LPS?
A
- A = stabilises membrane
- Core = charged, contributes to -ve surface -> reduces permeability to e.g. antibiotics.
- O = key in diagnosing disease (O serotypes), if lost = lower virulence.
10
Q
What is the Periplasm?
A
- Space between inner cytoplasmic and outer membranes.
- Gram -ve bacteria
- Gel consistency due to chock full of protein
11
Q
What 4 types of proteins are present in the Periplasm?
A
- Hydrolytic: break down polymers.
- Binding: begin transport
- Chemoreceptors: for chemotaxis
- Constructors: aid in synthesis of extracellular structures e.g peptidoglycan.
12
Q
What are porins?
A
- Pores in the outer membrane of gram -ve’s
- Transmission of small water-soluble molecules into periplasmic space.
13
Q
Specificity in Porins
A
Most Porins = non-specific
Some = specific
14
Q
Non-specific porins - how do they work?
A
- Water-filled channels
- Small hydrophilic substances diffuse through.
15
Q
Specific porins - how do these work?
A
- Contain a binding site for structurally similar targets
- E.g. E. coli w maltose selective LamB porin (Lambda = viral infection of EC)
