Chemotaxis Flashcards
Unidirectional Flagella
CW but stops and reorientates
Bundled flagella
When the pertrichous flagella move in same direction
Bundled flagella
When flagella goes in CCW direction and eventually spreads flagella to change direction
Define chemotaxis
The bias of movement towards region higher beneficial factors of lower toxic chemicals
Name 4 types of chemotaxis
Chemical - chemotaxis
Light - photo taxis
Heat - thermotaxis
Magnetic - magnetotaxis
How do bacteria detect changes
As bacteria are small they detect via changes over time and not changes on a single receptor
What are the 4 methyl accepting chemotaxis proteins
TSR - serine detected
TAR - aspartame, maltose
TAP - Dipepeptides
TRG - galactose, ribose
Example the cascade caused after methyl accepting protein
- First CheW activates CheA which is phosphorylated
- then phosphorylates either CheB or CheY
- CheY-P binds to motor and changes its direction
What’s CheA
Histidine kinase which causes autophsopolyration after Chew activates it.
What do CheB and CheY have in common
Response regulators
What is CheB
Methyl transferase that mediates adaption in conjunction with the chemotaxis methyl transferase CheR
What is CheZ
Specific phosphatase that dephosphorylates CheY-P allowing signal termination
How does bacteria respond to a signal in response to chemotaxis
Attractants reduce the amount of autophsphorylation of CheA
This promotes CCW to swim in straight line
Repellents increase autophsphorylation of CheA and cause CW and bundling
What is receptor adaption
The process of returning signalling state of chemotaxis pathway is reset
Adapted cells have tumbling bias allowing them to react negative or positive
Bacteria adapt to background levels by rapid signal termination (CheZ) or resetting signal proteins to non stimulated state.
This means that the bacteria won’t respond to background levels and only reacts to risk or desirable levels
What affects the rate of adaption by receptors
It depends on degree of methylation of specific glutamate residues in cytoplasmic domain of MCP (methyl accepting chemotaxis proteins)
CheR constitutive methyl transferase
CheB methyl transferase removes methyl groups, activity increased by phosphorylation by CheA
Methylation of glutamates by CheR increases chemoreceptors to activate CheA by auto phosphorylation causing more tumbling.
Adaption acts as a primary memory
