Flashcards
Lecture 14 PMB
Cards in this deck (20)
- 1chemotaxis"controlling the frequency of runs and tumbles to move toward attractants or away from repellents"
AND
"the movement of a cell toward or away from a chemical signal, amino acids, sugars, oxygen, electron acceptors" - 2Peritrichous CCW rotationmultiple flagella form a bundle and work together to propel the cell forward
"running" - 3Peritrichous CW rotationindividual filaments are pushed out of the bundle and stop working together
"tumbling"
reorients the cell randomly - 4How cells with a single flagellum change directioneither go from CCW to CW, or stop movement, reorient, and continue with same rotation
cell is reoriented randomly - 5How to test chemotactic ability of mutantsuse a soft agar and a compound that attracts bacteria + can be metabolized
--> cells at center metabolize the compound and swim out in a circle up the gradient they have created - 6baseline behavior of cellsalternate between runs and tumbles by switching flagellar direction, usually occurs in homogenous environment
- 7behavior of cells in presence of attractantkeep flagellum rotating in same direction, bias towards runs
- 8Why study chemotaxis?1) we can make and study a huge number of mutations that do not kill the cell!
2) signaling is incredibly sensitive
3) signaling is effective over a wide range of attractant concentrations
--> 2 & 3 let cells "see" a better environment - 9How do cells sense changes in levels of attractants/repellents and transmit info to flagellum?have MCP sensor proteins at the poles
external domain binds attractant in periplasm, HAMP domain transmits info of ligand binding, methylation region functions in adaptation, signaling region binds CheW and CheA --> relay info to downstream proteins - 10CheAHistidine Kinase that binds to signaling region of MCP
if attractants bind, it loses its phosphate group
will form trimers with CheW - 11CheYdownstream protein of MCP pathway that acts as a response regulator
- 12CheZdephosphorylates CheY-P (thus deactivating it)
- 13How do we get more runs than tumbles when more of an attractant binds?1) less CheA activity --> less CheA-P
2) Less of CheY-P
3) Less of CheY-P binding to FliM on flagellum
4) CheZ deactivates CheY
--> cause initial flagellar response to stimuli
--> less CW rotation, less tumbles
VICE VERSA FOR DECREASE IN ATTRACTANT - 14How does a bacteria know if it is swimming up a gradient of an attractant?not by spatial sensing but instead by TEMPORAL sensing
--> to do this they must reset signal system rapidly so that they can see if attractant concentration increases or decreases with respect to current level - 15CheA as a function of the amount of attractant outside the cellNOT a linear function because this is not a response to the absolute level, but instead the CHANGE in levels of the attractant
--> requires adaptation to the ambient level for every change in environment - 16Additional steps of adaptation if INCREASE in attractant levels1) CheR (always active) methylates MCP
2) CheA phosphorylates CheB LESS
3) CheB (response regulator) demethylates MCP LESS
--> cause buildup of methyl groups on MCP --> INCREASE ability to stimulate CheA --> return to pre-stimulus levels - 17Additional steps of adaptation if DECREASE in attractant levels1) CheR (always active) methylates MCP
2) CheA phosphorylates CheB MORE
3) CheB (response regulator) demethylates MCP MORE
--> cause depletion of methyl groups on MCP --> DECREASE ability to stimulate CheA --> return to pre-stimulus levels - 18summary of chemotaxismore attractant bind --> less CheA-P and less CheY-P
more CheY-P binding to FliM --> more tumbling
more methyl groups on MCP --> more ability to stimulate CheA phosphorylation
less methyl groups on MCP --> less ability to stimulate CheA phosphorylation - 19CheBmethylesterase that REMOVES methyl groups from MCPs and reduces their ability to activate CheA
- 20CheRmethyltransferase that constantly adds methyl groups to specific sites on MCPs, increasing their ability to activate CheA