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328 - Organisation of Bacterial Cells > 2 - Biomechanical World of Bacteria - Egbert > Flashcards

2 - Biomechanical World of Bacteria - Egbert Flashcards

1
Q

in what aspects of bacteria life (both intracellular and extracelular) does physics play a role? name the active and passive processes

A

INTRACELLULAR;

  • active; chromosome segregation, protein transport
  • passive; diffusion, quantum mechanics of biochemical reactions

EXTRACELLULAR;

  • active; mechanical forces generated during cell motility eg gliding, pilus retraction, flagella motility
  • passive; environmental specific mechanisms eg hydrodynamic forces, adhesive forces
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2
Q

what is Reynold’s number? give examples of 2 organisms, state the Reynolds number @ which they live at

A
  • dimensionless number comparing the magnitudes of inertia and viscous forces in a given flow. therefore allowing us to quanitfy the relative importance of these 2 forces
    HIGH REYNOLD’S NUMBER;
  • whales
  • > 10^4
  • dominated by inertia. therefore if to stop swimming in water then wouldnt come to a straight stop, would keep floating
    LOW REYNOLD’S NUMBER;
  • bacteria
  • < 10^-3
  • bacteria will come to a stop instantly if stop moving. dominated by viscosity
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3
Q

what would happen if we were to live at low Reynold’s number?

A
  • would experience Brownian motion as a result of non-uniform collisions with water molecules
  • water would have the viscosity of molasses (hence why bacteria stop immediately when stop swimming)
  • if we were to stop swimming, come immediately to .a halt
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4
Q

how do bacteria cells swim? in terms of Brownian motion etc

A
  • brownian motion causes the bacteria to rotate

- bacteria propel themselves using flagella

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5
Q

what does a large Reynold’s number mean for the body shape of aquatic animals?

A

all in a streamlined shape

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6
Q

what does a small Reynold’s number mean for the shape of water-living microorganisms?

A

can adopt any shape they want because inertia does not play much of a role
not required to be streamlined because not important
different shapes adapt to different conditions

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7
Q

how does a scallop swim?

draw a diagram showing scallop direction at R both below and above 1

A
  • swims in a reciprocal motion
  • opens shell then quickly closes it by squirting water out
  • 328 - 2 word
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8
Q

what does reciprocal mean in terms of movement?

A

changing its shape then returning to the original shape by going through the change in reverse

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9
Q

at low Reynold’s number, what type of movement works?

A

the movement can not be reciprocal

- based on the fact that inertia plays no role in movement

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10
Q

draw 3 hypothetical flagella structures. 2 must not be able to move @ low R and 1 must be able to move

A

328 . 2 word

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11
Q

give examples of 2 types of prokaryote that follow gliding motility. draw diagrams of each of their motions

A

eg cyanobacteria and myxobacteria

word

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12
Q

describe 3 hypothetical models of how gliding motility might work

A

FOCAL ADHESION;
- cells make contact points to the substrate which is anchored to the cytoskeleton proteins
HELICAL ROTOR;
- surface is deformed when the larger complex pushes into it and pushes the cell along
- the smaller complex does not affect the movement because it does not push into the substrate
NOZZLE;
- slime secreted from the back and the extension of the T IV pili and retraction helps to push the cell along

328 - 2

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13
Q

name the 5 physical phenomena that affect single bacteria on surfaces. draw a diagram to summarise these and show which direction the force is going

A
  • adhesion
  • shear stress
  • rheology
  • advection
  • diffusion
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14
Q

state the 3 main ways in which single cells can leverage fluid flow and give examples

A
  • surface colonisation eg Caulobacter crescentus
  • attachment through catch bonds eg E. coli
  • flow-directed movement eg Pseudomonas aeruginosa
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15
Q

how does fluid flow play a role in the attachment of C. crescentus?

A

the flow forces the cell to the bottom of the mix therefore allowing the holdfast to bind to the surface

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16
Q

draw the stucture of C. crescentus attached to a surface

A

word

17
Q

how does E. coli attach to surfaces? draw a diagram

A

through catch bonds
- FimH extends from FimA (stalk)
- in the low affinity structure, FimH is compressed. when in high affinity state it is in an elongated form
- when we apply force FimH starts to close around the mannose hence why we see that protein attachment is directly proportional to the force applied
328 - 2 word

18
Q

draw a graph of no. E. coli adhered to a surface against shear stress and explain relevant points of the graph

A

328 - 2 word

19
Q

which infections do the development of catch bonds play a role in?

A

E. coli infecting urogenital tract -> UTI

- even more handy because greater attachment with flow of urine

20
Q

draw a diagram and explain the movement of P. aeruginosa. DAG of this movement

A
  • T IV pili extend out and make connections with surface
  • pili disassemble and reassemble to pull the bacteria along the surface
  • this is AGAINST THE FLOW
    328 - 2 word
21
Q

draw a diagram of a bacterial community grouped together on a surface. what is the name given to these?

A

biofilms

328 - 2 word

22
Q

what are the 5 physical phenomena affecting cell communities on cell surfaces?

A
  • adhesion
  • shear stress/flow
  • rheology
  • advection
  • diffusion
23
Q

give an example of an organism, that in a biofilm state can form a fluid channel. DAG of this fluid channel formation

A

B. subtillis

24
Q

which bacterial species can form streamers? DAG of where these streamers are located within pipes and state what the initial steps are involved in this colonisation

A
  • P. aeruginosa
  • settle and form streamers where there is less flow because can attach > easily. then we get replication and colony growth
    328 - 2 word
25
Q

give a species that is involved in produce/cheater interactions and DAG of this interaction and explain it

A
  • Vibrio cholerae
    DIFFUSION;
  • producer cells initially adhere to the surface. release of carbohydrates eg GlcNAc attract other cheaters to the site where it is adhered.
  • cheater cells are dominant
    ADVECTION AND DIFFUSION;
  • when flow applied, the GlcNAc is washed away as well as the cheaters because no carbohydrate left
26
Q

what does M. xanthus form when under conditions of stress/starvation?

A

fruiting body, masses of cells all contained within one body.
inside, some differentiate into spores however around 80% die to provide nutrients etc for the other cells -> cooperativity

27
Q

give 2 examples of when the shape of colonies is influenced by the physical forces of flow etc

A

biofilms eg V. cholerae

and streamers eg P. aeruginosa

328 - Organisation of Bacterial Cells (4 decks)

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