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15 Cards in this Set
- Front
- Back
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Chemotaxis |
The mvmt of a cell toward or away from a chemical signal, AA, sugars, oxygen, e- acceptors ****Moves toward attractants and away from repellents**** |
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What is a run? |
CCW Multiple flagella form a bundle and work together to propel the cell forward |
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What is a tumble? |
CW - Individual filaments go "haywire" and stop working together - Tumbling reorients cell randomly! |
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What are 2 mechs bacteria with a single flagella use to change direction? |
1. CCW to move forward // CW to move backward on same line 2. CW rotation to move forward // cell stops, reorients then goes CW to move forward again |
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2 Assays for testing chemotaxis to a variety of compounds |
1. soft agar + compound that a. attracts bacteria & b. can be metabolized - cells inoculated @ center and swim around in circle up the gradient (6-48 hrs) 2. Agarose plug containing attractant placed in center of liquid and eats toward the bottom then outwards (takes minutes) |
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What does it mean to say chemotaxis is biased? |
cells in homogenous environment have a baseline behavior. --> If its getting closer to attractant, it will have a longer run. --> Further attractant results in more tumbles to reorient itself |
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Why study chemotaxis? |
1. chemotaxis= not essential for life; therfore, can mutate a lot w/o killing the cell 2. chemotaxis signaling is very sensitive--> can respond to very small changes 3. its effective over a wide range of attractant concen. |
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What parts make up MCPs? |
1. Periplasmic sensing domain-> binds attractant 2. HAMP domain transmits info of ligand binding to rest of protein 3. methylation region functions in adaptation 4. signaling region-> binds CheW & CheA (relays info to downstream proteins) |
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What do MCPs do? |
influence activiy of 2-component signaling proteins CheA= histidine kinase CheY= response regulator increase attractant binding= decrease in CheA-P |
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Mech behind more tumbles/ shorter runs |
decreased attractant binding to MCPs--> increased CheA activity (more CheA-P)--> more phototransfer to cheY (more cheY-P)--> more cheY-P binding to FliM--> CheZ deactivates CheY |
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Mech behind longer runs/ few tumbles |
increased attractant binding to MCPs--> decreased cheA activity (less CheA-P)--> Less phosphotransfer to cheY (Less CheY-P)--> Less cheY binding to FliM--> CheZ deactivates CheY |
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How does a bacterium know if it is swimming up a gradient? |
Temporal sensing mech Reset their signaling system rapidly to "feel" whether there is more attractant now than there was a sec ago |
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How does adaptation work? |
cell responds to changes in the amount of attractant in the environment. Continuously resets Baseline Dip= low->high concen. Spike= high-> low concen. |
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What causes more/ less ability to stimulate CheA? |
buildup of methyl groups on MCP = more ability to stimulate cheA fewer methyl groups on MCP= less ability to stimulate cheA |
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Fun Fact about Chemotaxis receptors |
* Chemotaxis receptors cluster at bacterial cell poles * Trimer clusters can influence each others signaling just because they're touching |
