Chemotaxis Flashcards
What does Counterclockwise flagella rotation accomplish
propels the cell forward
What does Clockwise rotation do?
Cause the cell to TUMBLE and reorientate in new direction
If their was increased attractant around what state would a cell be in?
Most likely the ‘run’ state which is CCW
if there is repellent the cell will tumble to get away
Heavy metals are examples of?
Repellents
What does chemotaxis imply?
the cell wants to go towards or away from a chemical
True or false, the bacteria controls the CW and CCW switch
False, reorientation is random. If there is a attractant gradient then the cell can detect this and make a random but progressive movement toward the attractant
If the cell is moving toward an attractant the run will be ___ and the tumble will be ___
the run will be long and the tumble will be less frequent
in the lab how would a cell behave near attractant that has been modified so that it cannot be up- taken by the cell at all.
The attractant still acts as an attractant and therefore the cell moves to it.
how do cells detect repellent and attractant?
they have chemo receptors inside the cytoplasmic membrane
Explain chemoreceptors
they have an N-terminus in the the periplasmic domain
they have a C-terminus in the cytoplasm
N interacts with incoming chemicals
C interacts with chemotaxis system
True or false, the N terminus is highly conserved
False, this is very distinct because different microbes interact with different chemicals
C terminus is conserved because the chemotaxis system is same typically
What Are MCP’s? list all.
- they are chemotaxis proteins clustered at the poles of the cell
- they are the chemoreceptors with N and C terminals
- Tsr, Tag, Trg, Tar, and Aer
True or false, MCP’s measure the concentration of chemicals in the environment and then send signals to chemotaxis system.
False, they only detect changes in concentration
Name the attractants and repellents Tar can detect.
A: Maltose and aspartate
R: Nickel and cobalt
Explain the signal transduction chemotaxis system up until CheA!!
1) ligand enters OM and binds to an MCP in its periplasm domain ( N-term)
2) this induces conformation change in C- term in cytoplasm
3) This change is detected by CheW which regulates CheA autophosphorylation
When does CheA autophosphorylation increase?
when attractant decreases or repellent increases! Think, if attractant is decreasing then the cell needs to change direction. To change direction CheA must phosphorylate
When does CheA autophosphorylation decrease?
If A is increasing or R is decreasing
Explain the process if the the cell is in an environment with decreasing attractant
1) MCP detects this
2) CheW tells CheA to phosphorylate
3) Phosphorylated CheA transfers its P group to CheY
4) CheY-P diffuses through the cytoplasm and interacts with a switch protein FliN, FliM, or FliG
5) tumble occurs
6) CheZ takes CheY off of switch (takes off P)
When is CheY not phosphorylated and why?
if cell is moving toward an attractant then autophosphorylation of CheA is decreased. Therefore CheY does not diffuse with a P group and switch is nog activated.
What are CheB and CheR?
Co-factors for the chemotaxis system
CheB is methylase
CheR is methylesterase
Explain the concept of a two component regulatory system
- very common
- one component is a histidine kinase
- one component is a response regulator
- There is phosphate transfer between them
In the chemotaxis system, what is the histidine kinase and what is the response regulator?
CheA is the kinase
CheY is the regulator
Explain chemotaxis adaptation? explain how MCP’s produce a signal for the cell to know what the environment is like.
MCP stands for methyl accepting chemotaxis protein. Essentially the chemotaxis system is measuring the over all methylation of the MCP’s. When an attractant is bound to an MCP it makes the MCP more readily methylated by CheB
comparing methylation levels of MCP’s tells the cell what?
comparing previous and current methylation levels of MCP’s can tell the cell whether concentration is going up or down.
