3-Bacterial Motility and Chemotaxis Flashcards
What energy is used to cause flagella to rotate?
Proton-motor force
What occurs when flagella rotate anti-clockwise?
They bundle together and the bacterium is propelled forward.
What occurs when the flagella rotate clockwise?
The bundle of flagella unravels and bacteria ‘tumble’ -> they change direction
What is ‘random walk’ in bacteria and when does it occur?
When ration of run and tumble in bacteria is random and movement is random.
Occurs in a homogenous environment. (no concentration gradient)
In presence of an environmental gradient is the ratio of tumble in favour of tumble or run?
In favour of run. Bacteria wants to move toward the good.
When it wants to stay, tumble is favoured.
What are the 5 general components of the flagellar motor structure?
1) Filament
2) Hook
3) Busher
4) Stater
5) Rotor
What is the filament?
The propellor
Hollow rigid cylinder made of subunits of the protein flagellin
What is the Hook?
The universal joint, allows torque generated by motor complex to change angle and direct filament orientation.
Links filament to the basal body.
What two rings is the ‘Bushing’ made of and what do they do?
L&P rings
L ring = outermembrane, p ring = cell wall, together acts as ‘bearing’ to allow motor to rotate without damaging the cell wall
What is the stator made of and what does it do?
Made of studs and C rings
It is the fixed point of the system, sits in the cell membrane
The MotA and MotB rings of the stator created channel for protons to pass through and generate torque.
What two rings is the Rotor made of? What do they do?
S and M rings
Moving part of the motor structure
What family of genes makes up the larges part of the motor structure system, the filament?
The FliC genes, takes 20,000 FliC units.
What secretion system is important in the assembly of the flagellar motor structure?
What part of the structure forms this secretion system and how does is work?
The type III secretion system. (Where proteins are secreted out a ‘needle’)
The basal body forms a specialised version.
The hollow filament forms the needle, with flagellin subunits (FliC monomoers) transported through the it. The subunits aggregate at the tip, example of self-assembly.
Filament grows at the tip not the base.
What effect does cAMP-CRP activation complex have on genes for flagellum expression?
Positively enhances the flhCD operon.
What does expression of flhC and flhD genes form?
Create trasncriptional activation complex that activates the expression of ‘middle genes’.
What does the sigma factor of the transcriptional complex do?
Is part of the RNA polymerase complex, it directs the complex to specfic classes of promotors so only some of the genes are expressed.
What is the sigma factor FliA responsible for?
Directing the complex toward the ‘late genes’
If FliA directs the complex to the late genes how are the middle genes expressed?
FlgM is an antisigma factor that is bound to FliA and inactivates it while the middle genes are being expressed.
Once the middle genes are finished being expressed it detaches and FliA is free to direct the complex to the late genes
Flagella in E. coli and salmonella are arranged peritrichously. What does this mean?
What alternative arrangement of flagella do V. cholera have?
Peritrichously = spread all over the entire surface of the bacterium
Single flagella at the Cell - pole
What is phase variation?
Very common in pathogenic bacteria
Random switching between expressing one surface protein to another antigenically distinct surface protein to evade the host defences.
Salmonella randomly switch from FliC to FljB, an alternative propeller subunit.
What does fljA gene do?
It represses FliC expression.
What does fljA and fljB being expressed from the same operonic promotor ensure?
That only one filament protein is turned on at a given time, i.e. only Flic or FljB
Does fljA act block transcription or translation of FliC?
How does this differ from lacI repressor?
fljA blocks translation of FliC
fljA acts post-transcriptionally, by blocking translation of FliC mRNA
What controls the FljB - FljA operon?
The inverted repeat sequences hixL hixR
they are the same seqeunce orientated in opposite directions
What are NAPs?
Nucleated associated proteins. Responsible for structuring DNA in nuclei in highly organised way. Structure of DNA v. important in gene expression regulation.
Master regulators
Name two architectural DNA binding proteins
HU- helps small loop formation of Hin invertasome
FIS - Enhances Hin activity by stabilising DNA in the invertasome
What is chemotaxis system?
Sensory system of bacteria.
Enables them to sense evironment, detect signals & alter behaviour/ respond.
E.g change run:tumble ratio
What is the basic outline of signal transduction?
Sensor protein attached to transmitter protein that contains a conserved histidine residue.
Receiver domain with conserved aspartic acid attached to output domain.
Structure of sensor protein changes when it receives a signal.
This conformational change causes histidine in transmitter to become phosphorylated.
This phosphorylates receiver domain of output protein on conserved aspartic acid residue.
Structural change on output domain results in an action, e.g activation/suppression of gene expression.
Outline the ubiquitous regulatory bacterial chemotaxis system
Sensor histidine kinase, embedded in cell membrane (MCP)
MCP detects signal from outside the cell
This initiates a signal cascade causing phosphorylation of aspartic acid on output side
What are MCP’s?
Methyl-accepting Chemotactic Proteins.
Each composed of up-down-up-down four helix bundles.
First and last helices extend into the cytoplasm.
Ligand induced conformational changes result in inhibition of CheA kinase.
