2. Bacterial Motility And Adhesion Flashcards
1
Q
How is peptidoglycan structured around the bacterial cell? 3
A
- Not sheet like
- Forms ribbon like structures
- Ribbons form helical structures around bacterium
2
Q
Describe peptidoglycan side chains. 6
A
- Gram negative, and the odd gram positive, have a tetra peptide chain of L-ala D-glu DAP D-ala
- Direct link between DAP and side chain
- DAP only found in peptidoglycan and D amino acids rare elsewhere
- Gram positive side chain connected to L-ala D-glu L-lys D-ala at L-lys via an interbridge
- Interbridge has five amino acids which can vary between organisms
- Formation of peptidoglycan bridges by transpeptidase/carboxypeptidase
3
Q
What are the properties of peptidoglycan? 6
A
- Gram negative it is one late thick, low cross linking of NAM to NAM, 25%
- Gram positive, many layers thick with high crosslinking of nam-nam, 75%
- Represents fifty percent of weight of gram positive cells
- Laid down in cables approx 50nm wide made of several crosslinked glycan strands which get smaller towards poles
- Penicillin inhibits crosslinking of peptidoglycan, which destroys integrity and cells fall apart
- Lysozyme also breaks peptidoglycan
4
Q
Describe gram positive cell walls. 4
A
- Homogenous
- Single layer (20-80nm) in electron microscope
- Contains 80% peptidoglycan and some teichoic acid
- Teichoic acid is a polymer of ribitol phosphate, which is covalently bonded to NAM in peptidoglycan
5
Q
Describe gram negative bacteria. 5
A
- Heterogenous cell wall with multiple layers
- Outer membrane is made of lipopolysaccarides, proteins (porins) and lipids
- Thin layer of peptidoglycan
- Periplasmic space on both sides of PG layer
- Cytoplasmic membrane
6
Q
Describe the surfaces of gram positive and negative bacteria. 4
A
- Gram positive have a smooth surface under the scanning electron microscope
- Gram negative have a ruffled surface under scanning electron microscope
- This is due to the heterogenous layer
- Vesicles bleb from outer membrane
7
Q
Describe lipopolysaccharides as found on the membrane of gram negative bacteria. 6
A
- LPs composed of sugars projecting away from the cell surface and a lipid a embedded in the membrane outer leaflet
- Hetero-/o-specific polysaccharide side chain is highly variable
- Protects from complement
- Core polysaccharide is always the same
- It holds the cell together, organisms are not viable without it
- Lipid a/endotoxin in outer membrane made from fatty acyl chains - the number and structure of these changes the toxicity
8
Q
Describe LPS lipid a. 6
A
- Lipid a causes endotoxin shock, leading to multi organ failure and death, but fewer chains mean less toxicity
- Causes vasoconstriction, vascular leakage, systemic clotting in capillaries so drugs trying to target lipid a
- Good in small quantities - alerts immune system
- Antibiotics make endotoxic shock worse
- Causes membrane breakdown so more lipid a released into system
- Steroids must also be used in treatment to dampen the immune response
9
Q
How do you view bacterial cell structure? 5
A
- Thin sections (for TEM) show inside bacteria and surface features
- Sections must be embedded in a hard, polymeric substance, dyed and sliced
- Resolution in TEM is 2nm
- Essential structures:
Membrane
Wall
Nucleoid
Ribosomes - Optional extras:
Flagella
Fimbriae
Capsule
Slime
Inclusion bodies
10
Q
What are flagella? 6
A
- Flagella allow swimming
- Can be polar (at one end) or peritrichous (many, these bacteria are highly motile)
- Found in prokaryotes, eukaryotes and archaea
- Eukaryotic flagella bend, different movement
- Position of flagella on bacteria is variable
- Sometimes used in chemotaxis, towards attractants or away from repellents
11
Q
Describe polar, helical flagella. 2
A
- Rigid flagellum rotates, whips and thrashes
2. Engine like structure moves bacteria
12
Q
Describe a polar tuft of flagella. 5
A
- Group of flagella rotate
- Flagella are highly rigid, not soft and pliable. Can’t bend
- Thethered into outer membrane/cell wall
- Can link together to form one thick flagella
- Move quite fast
13
Q
Describe peritrichous, helical flagella. 3
A
- Many of them
- Organism eg proteus vulgaris moves very quickly
- Random movement in all directions
14
Q
Describe a polar flagella bundle. 3
A
- Bundle rotates to push cell forward
- Smooth swimming
- Perfectly straight line
15
Q
What are the properties of flagella? 6
A
- Helical and rigid
- 20nm diameter
- Polymer of a single protein in subunits called flagellin
- Anchored into cytoplasmic membrane of cell
- Biological rotary motor at base
- Driven by biological electricity due to protons
16
Q
What is the structure of a flagellum? 4
A
- L and p rings act as a bushing
- Hook going into membrane transfers rotary motion to the filament
- Motor proteins surrounding the anchor conduct electric current from the periplasm to the cytoplasm
- This electric power flows into the m ring where it is converted into rotary motion
17
Q
What are fimbriae/pili? 6
A
- Fimbriae are often peritrichous
- Straight or flexible, over one hundred per cell
- Carry proteins called adhesins which attach to receptors on substratum (host cells) eg E. coli attaches to mannose receptors to cause urinary tract infections
- This protects them from sheer forces and helps them obtain nutrients
- A polymer of protein forms the shaft
- Fimbriae are shorter and thinner than flagella.
18
Q
Describe peritrichous type one straight fimbriae, like that found on E. coli. 3
A
- Helically wound protein subunits
- Collection of proteins at tip for adhesion
- These bind to mannose residues on epithelial cells
19
Q
Describe the structure of P fimbriae. 6
A
- P fimbriae bind to digalactoside residues of epithelial cells
- PapC protein forms basal export structure, allowing fimbriae to form
- Hollow tubes which polymerise in a helical manner
- In the cytoplasm, papA moves through the hole and deposits on top for growth
- PapG is the only protein that allows bacteria to hind to epithelial cells - it’s at the top
- PapF and papK are adaptor proteins, and papE is a fibrillar protein
20
Q
Describe the complex structure of peptidoglycan in detail. 6
A
- Peptidoglycan aka mucopeptide or murein sacculus
- There are 10-65 sugars (NAM and NAG) per chain
- Without peptide cross bridges/side chains, the backbone would separate easily
- 30-60% of nam are cross linked, and this varies between organisms so fewer cross links means more flexibility
- 100 types of peptidoglycan, with diversity focussed on crosslinks and side chains
- Universally conserved across prokaryotes only
