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Microbes, Man And The Environment > 2. Bacterial Motility And Adhesion > Flashcards

2. Bacterial Motility And Adhesion Flashcards

1
Q

How is peptidoglycan structured around the bacterial cell? 3

A
  1. Not sheet like
  2. Forms ribbon like structures
  3. Ribbons form helical structures around bacterium
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2
Q

Describe peptidoglycan side chains. 6

A
  1. Gram negative, and the odd gram positive, have a tetra peptide chain of L-ala D-glu DAP D-ala
  2. Direct link between DAP and side chain
  3. DAP only found in peptidoglycan and D amino acids rare elsewhere
  4. Gram positive side chain connected to L-ala D-glu L-lys D-ala at L-lys via an interbridge
  5. Interbridge has five amino acids which can vary between organisms
  6. Formation of peptidoglycan bridges by transpeptidase/carboxypeptidase
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3
Q

What are the properties of peptidoglycan? 6

A
  1. Gram negative it is one late thick, low cross linking of NAM to NAM, 25%
  2. Gram positive, many layers thick with high crosslinking of nam-nam, 75%
  3. Represents fifty percent of weight of gram positive cells
  4. Laid down in cables approx 50nm wide made of several crosslinked glycan strands which get smaller towards poles
  5. Penicillin inhibits crosslinking of peptidoglycan, which destroys integrity and cells fall apart
  6. Lysozyme also breaks peptidoglycan
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4
Q

Describe gram positive cell walls. 4

A
  1. Homogenous
  2. Single layer (20-80nm) in electron microscope
  3. Contains 80% peptidoglycan and some teichoic acid
  4. Teichoic acid is a polymer of ribitol phosphate, which is covalently bonded to NAM in peptidoglycan
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5
Q

Describe gram negative bacteria. 5

A
  1. Heterogenous cell wall with multiple layers
  2. Outer membrane is made of lipopolysaccarides, proteins (porins) and lipids
  3. Thin layer of peptidoglycan
  4. Periplasmic space on both sides of PG layer
  5. Cytoplasmic membrane
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6
Q

Describe the surfaces of gram positive and negative bacteria. 4

A
  1. Gram positive have a smooth surface under the scanning electron microscope
  2. Gram negative have a ruffled surface under scanning electron microscope
  3. This is due to the heterogenous layer
  4. Vesicles bleb from outer membrane
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7
Q

Describe lipopolysaccharides as found on the membrane of gram negative bacteria. 6

A
  1. LPs composed of sugars projecting away from the cell surface and a lipid a embedded in the membrane outer leaflet
  2. Hetero-/o-specific polysaccharide side chain is highly variable
  3. Protects from complement
  4. Core polysaccharide is always the same
  5. It holds the cell together, organisms are not viable without it
  6. Lipid a/endotoxin in outer membrane made from fatty acyl chains - the number and structure of these changes the toxicity
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8
Q

Describe LPS lipid a. 6

A
  1. Lipid a causes endotoxin shock, leading to multi organ failure and death, but fewer chains mean less toxicity
  2. Causes vasoconstriction, vascular leakage, systemic clotting in capillaries so drugs trying to target lipid a
  3. Good in small quantities - alerts immune system
  4. Antibiotics make endotoxic shock worse
  5. Causes membrane breakdown so more lipid a released into system
  6. Steroids must also be used in treatment to dampen the immune response
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9
Q

How do you view bacterial cell structure? 5

A
  1. Thin sections (for TEM) show inside bacteria and surface features
  2. Sections must be embedded in a hard, polymeric substance, dyed and sliced
  3. Resolution in TEM is 2nm
  4. Essential structures:
    Membrane
    Wall
    Nucleoid
    Ribosomes
  5. Optional extras:
    Flagella
    Fimbriae
    Capsule
    Slime
    Inclusion bodies
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10
Q

What are flagella? 6

A
  1. Flagella allow swimming
  2. Can be polar (at one end) or peritrichous (many, these bacteria are highly motile)
  3. Found in prokaryotes, eukaryotes and archaea
  4. Eukaryotic flagella bend, different movement
  5. Position of flagella on bacteria is variable
  6. Sometimes used in chemotaxis, towards attractants or away from repellents
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11
Q

Describe polar, helical flagella. 2

A
  1. Rigid flagellum rotates, whips and thrashes

2. Engine like structure moves bacteria

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12
Q

Describe a polar tuft of flagella. 5

A
  1. Group of flagella rotate
  2. Flagella are highly rigid, not soft and pliable. Can’t bend
  3. Thethered into outer membrane/cell wall
  4. Can link together to form one thick flagella
  5. Move quite fast
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13
Q

Describe peritrichous, helical flagella. 3

A
  1. Many of them
  2. Organism eg proteus vulgaris moves very quickly
  3. Random movement in all directions
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14
Q

Describe a polar flagella bundle. 3

A
  1. Bundle rotates to push cell forward
  2. Smooth swimming
  3. Perfectly straight line
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15
Q

What are the properties of flagella? 6

A
  1. Helical and rigid
  2. 20nm diameter
  3. Polymer of a single protein in subunits called flagellin
  4. Anchored into cytoplasmic membrane of cell
  5. Biological rotary motor at base
  6. Driven by biological electricity due to protons
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16
Q

What is the structure of a flagellum? 4

A
  1. L and p rings act as a bushing
  2. Hook going into membrane transfers rotary motion to the filament
  3. Motor proteins surrounding the anchor conduct electric current from the periplasm to the cytoplasm
  4. This electric power flows into the m ring where it is converted into rotary motion
17
Q

What are fimbriae/pili? 6

A
  1. Fimbriae are often peritrichous
  2. Straight or flexible, over one hundred per cell
  3. Carry proteins called adhesins which attach to receptors on substratum (host cells) eg E. coli attaches to mannose receptors to cause urinary tract infections
  4. This protects them from sheer forces and helps them obtain nutrients
  5. A polymer of protein forms the shaft
  6. Fimbriae are shorter and thinner than flagella.
18
Q

Describe peritrichous type one straight fimbriae, like that found on E. coli. 3

A
  1. Helically wound protein subunits
  2. Collection of proteins at tip for adhesion
  3. These bind to mannose residues on epithelial cells
19
Q

Describe the structure of P fimbriae. 6

A
  1. P fimbriae bind to digalactoside residues of epithelial cells
  2. PapC protein forms basal export structure, allowing fimbriae to form
  3. Hollow tubes which polymerise in a helical manner
  4. In the cytoplasm, papA moves through the hole and deposits on top for growth
  5. PapG is the only protein that allows bacteria to hind to epithelial cells - it’s at the top
  6. PapF and papK are adaptor proteins, and papE is a fibrillar protein
20
Q

Describe the complex structure of peptidoglycan in detail. 6

A
  1. Peptidoglycan aka mucopeptide or murein sacculus
  2. There are 10-65 sugars (NAM and NAG) per chain
  3. Without peptide cross bridges/side chains, the backbone would separate easily
  4. 30-60% of nam are cross linked, and this varies between organisms so fewer cross links means more flexibility
  5. 100 types of peptidoglycan, with diversity focussed on crosslinks and side chains
  6. Universally conserved across prokaryotes only

Microbes, Man And The Environment (18 decks)

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