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MICR3330 > 6 - Flagella, Motility & Taxis > Flashcards

6 - Flagella, Motility & Taxis Flashcards

1
Q

Types of prokaryote motility

A
  • Flagella
  • Gliding
  • Twitching
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2
Q

Flagella

A

Helical, thread-like appendages extending from the plasma membrane and cell wall that enable motility

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3
Q

Types of flagellar arrangement

A
  • Monotrichous (single, polar flagellum)
  • Amphitrichous (single flagella at opposite ends of cell)
  • Lophotrichous (Flagella cluster at one or both ends)
  • Peritrichous (flagella spread over cell-surface)
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4
Q

Three main parts of flagella

A
  • Filament
  • Hook
  • Basal body
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5
Q

Filament

A
  • Hollow, rigid cylinder composed of flagellin protein molecules
  • Synthesised by transfer of flagellin subunits through the hollow filament
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6
Q

Flagella genes

A
  • Over 50 genes control flagella synthesis and function
  • Half encode structural components
  • The rest control regulation of flagella assembly
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7
Q

3 main flagella genes

A

fla, fli and flg

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8
Q

Sheaths

A

Membraneous or lipopolysaccharide surrounding the filament

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9
Q

Hook

A

Composed of protein and acts as a flexible coupling between the filament and basal body

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10
Q

Basal body

A
  • Attaches flagellum to the cell
  • Functions as the flagellum motor
  • Consists of rings attached to a central rod
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11
Q

Basal body of gram negative bacteria

A
  • Four rings surround central rod
  • L ring (embedded in
    lipopolysaccharide)
  • P ring (embedded in
    peptidoglycan)
  • MS ring (embedded in
    plasma membrane)
  • C ring attaches to the MS
    ring on the cytoplasmic side
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12
Q

P & L ring function

A
  • Act like bearings
  • Gap between them and rod allows rod to rotate
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13
Q

MS and C rings function

A
  • Act as rotor
  • Rotate within the membrane and turn rod attached to them, and the
    filament attached to the rod
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14
Q

Basal body of gram positive bacteria

A
  • Two rings connected to the central rod
  • An inner ring connected to the plasma membrane
  • An outer ring attached to peptidoglycan
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15
Q

Proteins are associated with the basal body

A
  • Mot A
  • Mot B
  • Fli Proteins
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16
Q

Mot A and B proteins

A
  • Provide a proton channel through the plasma membrane and rotate the flagellum
  • Mot B also anchors the complex to peptidoglycan layer
17
Q

Fli proteins

A
  • Important in generating flageller rotation
  • Also involved in switching the direction of rotation
18
Q

Flagellar rotation

A
  • Filament rotation acts like
    the propeller of a boat
  • The bacterial cell rotates if the flagellum tip is artificially tethered
  • Proton Motive Force drives rotation
19
Q

Proton Motive Force rotation

A
  • Protons move down a charge and pH gradient
  • H+ flow occurs at Mot protein channel
  • Entry of a proton into the channel gives a small push
  • Protons exert electrostatic forces on charges present in C and MS rings
  • Rotation speed is proportional to the PMF
20
Q

How many protons required for one complete rotation

A

~1000

21
Q

Peritrichous flagella movement

A
  • Counterclockwise rotation causes running
  • Clockwise rotation causes tumbling (disrupts a run)
  • Cells move off in new direction
22
Q

Polar flagella movement

A
  • Cells move forward or backward by reversing flagellar rotation
  • CCW rotation pushes, CW rotation pulls the cell
23
Q

Flagellar movement in a homogeneous environment

A
  • The direction of bacterial motility is random
  • Straight runs are interspersed with tumbles that result in random directional changes when running resumes
24
Q

Taxis responses in prokaryotes

A

Directed movement to attractants and from repellents

25
Q

Chemotaxis

A
  • Involves biased random walk
  • Longer runs occur moving up a nutrient gradient towards attractant (tumbling occurs less frequently)
26
Q

Chemotaxis mechanism

A
  • Prokaryotic cells sense concentration changes over time
  • Changes are detected through periodic (temporal) sampling of the environment
  • Chemoreceptors called MCPs detect attractants and repellents
  • Complex two component phosphorelay system regulates directional rotation of flagella
27
Q

What does MCPs stand for

A

Methyl-accepting chemotaxis proteins

28
Q

Where are MCPs found

A

In plasma membrane

29
Q

MCPs

A
  • MCPs bind chemicals directly or indirectly via periplasmic binding proteins
  • Some MPCs can detect both attractants and
    repellants
  • Detect one or more ‘types’ of attractant (e.g. specific
    amino acids/sugars/light)
30
Q

Two component phosphorelay system that regulates directional rotation

A
  • Involves sensor kinase CheA and response regulator CheY
  • If attractant levels decrease (cell moving away), less attractant bound, MCPs activate CheA to increase rate of autophosphorylation and CheA-P transfers P to CheY
  • Phosphorylated CheY-P diffuses to flagellar motor, causes clockwise flagella rotation (tumbling)
  • If attractant levels increase (cell moving towards it), converse occurs (runs)
  • CheY-P interacts with flagellar motor to induce CW rotation (tumbling), while CheY cannot bind to flagellar motor
  • Tumbling does not continue indefinitely: after a few secs the phosphoryl group is removed from CheY-P by CheZ protein, thus CCW rotation is restored
31
Q

MCP clusters

A
  • MCPs form clusters associated with CheA and CheW proteins
  • Seen at either end of cell
  • MCP clusters work cooperatively to modulate CheA activity
32
Q

Adaptation

A
  • Once cell has successfully responded to an attractant, it must stop responding and reset the sensory system to await further signals
  • Involves the methylation of MCPs
33
Q

Methylation of MCPs

A
  • 1-5 methyl groups can be added to MCPs
  • Gradually reducing response (when fully methylated they no longer respond to attractants)
  • Despite the continued presence of attractant, CheA activity is eventually restored to the same value as it had in the absence of attractant
  • Methylation and demethylation of MCPs occurs more slowly than the phosphorylation of CheA and CheY
34
Q

In adaptation, is the cell detecting the absolute concentration of a chemical?

A

No, it is monitoring small changes in the concentrations of both attractants (and repellants) over time

35
Q

Phototaxis

A

Taxis response to light

36
Q

Aerotaxis

A

Taxis response to oxygen

37
Q

Magnetotaxis

A

Certain gram negative microaerophilic and anaerobic bacteria contain certain membrane bound magnetite or magnetosomes

38
Q

Original hypothesis for the function of magnetotaxis

A
  • Magnetosomes function like compass needle, orientating bacteria along Earth’s
    magnetic field
  • Magnetosomes thus enable microaerophilic and anaerobic bacteria near magnetic poles to swim down towards the sediment, to microaerophilic or anoxic conditions
39
Q

Current hypothesis for the function of magnetotaxis

A
  • Magnetotaxis functions in
    conjunction with aerotaxis
  • Cells orient along magnetic field, then respond to O2 levels
  • Can swim in both up and down directions (CW pull or CCW push)
  • Reach their preferred O2
    concentration (the OATZ)

MICR3330 (29 decks)

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