Lecture 6 - Flagella, motility and axis Flashcards
Describe the general features of a flagellum
- Rigid, helical from PM and CW
- 20nm across, 20um long
What are the 4 different types of flagella?
- Monotrichous = single polar
- Amphitrichous = both sides
- Lophotrichous = cluser at 1/both ends
- Peritrichous = spread over cell surface
List the 3 main parts of the flagellum’s structure and briefly describe their function
- Filament = hollow rigid cylinder with flagellin S + F proteins eg fla, fli, flg
- Hook = flexible protein coupling between filament and basal body
- Basal body = motor = rings and central rod, attaches flagellum to cell
List the S+F of the G-ve basal body
- L ring in LPS of OM
- P ring in PG
- MS ring in PM
- C ring attached to MS in cytoplasm
- P and L = bearings with gap for rotation
- MS and C = rotor for rotation
List the S+F of the G+ve basal body
- Inner ring in PM
- Outer ring in PG
What are the 3 basal body associated proteins and their function?
- Mot A and B = proton channel thru PM for rotation
- Mot B also anchors complex to PG
- Fli proteins = generate rotation and switch directions
What drives the rotation of the flagellum and how?
- PMF = protons move down charge/pH gradient
- PMF creates push when H+ enters Mot protein
channel - Protons = electrostatic forces on charges in C and MS rings
How is a flagellum like a 2 part motor producing torque? Use an electrical motor as a metaphor
- Rotor = C ring of Fli proteins and MS ring
- Stator = Mot A and B proteins forming channel
What are the 2 directions of rotation for polar flagella? What is actually observed in some cases?
- CCW rotation pushes forward and CW rotation pulls backward
- Run and arc = linear forward, backward arc
- Run reverse flick = sudden bend in hook/filament creates flick
What are the 2 directions of rotation for peritrichous flagella?
Counterclockwise running and clockwise tumbling to change direction
What sort of movement is noted in a homogenous environment?
Random walk = straight runs and tumbles at random
Define a taxis response
Directed movement to attractants and from repellents
What movement is noted during chemotaxis if an attractant was present vs a repellent?
- Biased random walk = longer runs up nutrient gradient towards attractant with less tumbling
- Shorter runs and more tumbling if repellent
Do bacteria detect the absolute conc or just the conc changes? How do they detect conc?
- Detect small changes over time by periodic sampling
- Methyl-accepting chemotaxis proteins (MCPs) as chemoreceptors in PM
- Bind chemicals with periplasmic binding proteins
What sort of system regulates directional rotation of flagella and what are its components?
2 component phosphorelay system with sensor kinase CheA and response regulator CheY
Describe the 4 step process the phosphorelay system goes through if there was a decreased attractant/cell moving away/less attractant bound
- MCPs activate CheA = increase autophosphorylation
- CheA-P transfers P to CheY
- CheY-P diffuses to flagella motor = CW rotation/tumbling
- CheZ removes P from CheY-P after few secs = restore CCW rotation/run
What do MCPs cluster with in the cell and where?
With CheA and CheW proteins at either ends to modulate CheA
Once a successful response to an attractant has been completed, how does the cell stop the response? What is the function of such an adaptation?
- 1-5 methyl groups added to MCPs to gradually reduce response over sec-mins until no response
- Reset sensory system to compare current and previous conditions (short memory)
What is phototaxis, what bacteria do it and why?
Taxis to light by phototrophic microbes for orientation to optimum intensity and wavelengths for photosynthetic pigments
Which bacteria undergo magnetotaxis and how?
Some G-ve microaerophilic and anaerobic with membrane bound magnetite or magnetosomes aligned with MamK protein
Describe the hypothetical function of magnetosomes and why these bacteria undergo it
- Magnetotaxis works with aerotiaxis = microaerophilic and anaerobic bacteria orient along magnetic field then orient to optimum O2 levels
- Magnetosomes seek whatever hemisphere then bacteria able to swim down
