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Phys-Pro - Section 1 > Motility > Flashcards

Motility Flashcards

1
Q

Flagellum - basic structure and functions

A

Long, threadlike proteinaceous structures
Also called H-antigen
Responsible for motility

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2
Q

3 components of the flagellum

A

Hook, filament, basal body

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3
Q

structure of the filament

A

Hollow structure made of flagellin proteins arranged in a helix
-not the same in all bacteria

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4
Q

structure of the hook

A

Made up of repeating units of a single protein

Also has hook associated proteins to link the hook to the filament

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5
Q

Function of the basal body

A

To anchor the hook and filament to the cell envelope

-uses a rod and integral rings

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6
Q

How many/which basal body rings are present in gram + bacteria?

A

there are 2 rings, the S&M rings

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7
Q

How many/which basal body rings are present in gram - bacteria?

A

There are 4 rings, the S, M, L and P rings

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8
Q

The motor consists of 2 parts, what are their functions

A

Rotor: part that moves

Stator: fixed component against which the rotor moves

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9
Q

What components make up the stator?

A

made up of multiple copies of MotA and MotB proteins which forms a complex around the SM ring
-called the Mot complex

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10
Q

What components make up the rotor?

A

FliG protein, the C and SM rings.

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11
Q

How does the Mot complex undergo conformational changes?

A

Allows passage of protons into the cell through the motor
-the sequential passage of protons induces conformational changes in the Mot proteins that drive the attached motor through rotation steps and generate torque

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12
Q

What is the role of the rod of the basal body?

A

transmits the rotation of the SM and C rings across the periplasm and out of the cell

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13
Q

What is the role of the P and L rings (for gram neg bacteria) ?

A

to form a bushing through the peptidoglycan and outer membrane

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14
Q

what does the “universal joint” feature of the hook mean?

A

It allows filament to rotate while pointing in any direction outside of the cell.

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15
Q

4 steps in proton passage through and conformational change of the Mot complex

A
  1. Proton flow drives the cyclical conformational change in the stator
    - stator transmits this force to the rotor
  2. Correct alignment of the rotor with the stator triggers an opening in the stator, allowing a proton to enter which binds to Asp23 on the Mot complex
  3. Proton binding to Asp23 forces a conformational change which is transmitted to the rotor, causing it to rotate through a small angle
  4. The proton is released into the cytoplasm, reversing the conformational change and causing further rotation
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16
Q

Switch - location and role

A

Located beneath the basal body

It’s job it to change the direction of rotation of the flagella

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17
Q

3 proteins that constitute the switch

A

FliG, FliN, and FliM

18
Q

What 2 proteins make up the C ring

A

FliM and FliN

19
Q

What is the job of CheY-P

A

important for switching flagellar rotation during chemotaxis

  • binds to FliM
  • switches back and forth between it’s phosphorylated and dephosphorylated forms
  • the phosphorylated form tells the flagella to switch directions
20
Q

What is the role of FliG in the switch

A

binds to the SM ring as well as FliM and FliN

21
Q

Movement towards a favourable stimuli is called

A

positive taxis

22
Q

Movement away from an unfavouable stimuli is called

A

negative taxis

23
Q

Runs : movements in a single direction for some time due to ____ flagellar rotation

A

counterclockwise

-the rotation generates a helical wave that pushes the cell forward

24
Q

Rotation of the flagellum in the clockwise direction results in?

A

A tumble: abrupt, random changes in direction

-unbundles the flagella if there are multiple ones

25
Q

Magnetotaxis

A

Small granules of iron in some sea bacteria allow them to orient themselves in the magnetic field

26
Q

What is an advantage of the run/tumble method?

A

the run/tumble allows bacteria with multiple flagella to untangle their flagella (which can get tangled up during a run if they’re all rotating in the same direction)

27
Q

Basic principle of chemotaxis:

A

Bacteria move away from toxic compounds and towards nutrients

28
Q

What determines the length of each run or tumble?

A

Nutrient or toxic gradients
-If a cell is running up a conc gradient, it detects the increasing concentration and delays the onset of the next tumble; runs that do not carry the cell to higher attractant concentrations are shorter than those that don’t

29
Q

changes in concentration of the environment are sensed over ___?

A

Time

  • use temporal gradients
  • distances would be too minute to detect
30
Q

What type of regulatory mechanism is used in chemotaxis

A

a 2 component regulatory system

31
Q

What are the main 2 methyl-accepting chemotaxis proteins of the system

A

CheY and CheA

  • are transmembrane proteins
  • CheY is a responder
  • CheA is a cytoplasmic receptor
32
Q

What are the 4 other proteins involved

A

CheB, CheW, CheZ, CheR

33
Q

methyl-accepting chemotaxis proteins - features

A

Span the entire membrane

are dimers

Mechanism of chemotactic message relay is unknown

34
Q

Methylation of MCPs occurs on what residue

A

The glutamate residue

  • each protein has about 4-5 glutamate residues
  • allows for the bacteria to adjust to increasing concentrations by increasing the degree of methylated sites

*methylation is reversible

35
Q

CheA function

A

sensor histidine kinase: autophosphorylates upon sensing a signal
-phosphorylates CheY to pass on signal

36
Q

CheY function

A

response regulator.

The phosphorylated CheY (CheY-P) binds to the flagellar motor switch to initiate the reverse (clockwise) rotation.

37
Q

CheZ function

A

A phosphatase that removes the phosphate from Chey-P

38
Q

CheW function

A

Membrane protein that controls the rate of autophosphorylation of CheA

39
Q

CheR

A

Methytransferase that methylates MCPs

40
Q

CheB

A

is also a response regulator. CheB-P is a methylesterase that removes the methyl group from methylated MCPs.

41
Q

6 steps in signal transduction during chemotaxis in E.coli

A
  1. Attractants/repellants bind to MCPs (Tar etc). MCPs are methylated by CheR.
  2. CheW-dependent auto-phosphorylation of CheA is activated. Attractants reduce the rate of autophosphorylation; while repellants increase the rate.
  3. CheA-P passes the phosphoryl group to CheY and CheB.
  4. CheY-P interacts with the switch proteins (FliMNG) to cause clockwise rotation and tumbling.
  5. CheB-P removes methyl groups from MCPs. CheB-P and CheR works together to control the levels of methylation on MCPs.
  6. Attractants reduces tumblings and promote CCW flagellar rotation and smooth swimming, while repellants promote CW rotation and tumblings.
42
Q

What does adaptation mean in the context of chemotaxis

A

Bacterium becomes desensitized to an attractant at a certain concentration

  • will start to tumble more and stay in the area
  • if an area of higher concentration is detected, tumbling is repressed and it “runs” to the area of higher concentration

Phys-Pro - Section 1 (8 decks)

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