Chemotaxis

Question 1

What does Counterclockwise flagella rotation accomplish

Answer 1

propels the cell forward

Question 2

What does Clockwise rotation do?

Answer 2

Cause the cell to TUMBLE and reorientate in new direction

Question 3

If their was increased attractant around what state would a cell be in?

Answer 3

Most likely the ‘run’ state which is CCW

if there is repellent the cell will tumble to get away

Question 4

Heavy metals are examples of?

Answer 4

Repellents

Question 5

What does chemotaxis imply?

Answer 5

the cell wants to go towards or away from a chemical

Question 6

True or false, the bacteria controls the CW and CCW switch

Answer 6

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

Question 7

If the cell is moving toward an attractant the run will be ___ and the tumble will be ___

Answer 7

the run will be long and the tumble will be less frequent

Question 8

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.

Answer 8

The attractant still acts as an attractant and therefore the cell moves to it.

Question 9

how do cells detect repellent and attractant?

Answer 9

they have chemo receptors inside the cytoplasmic membrane

Question 10

Explain chemoreceptors

Answer 10

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

Question 11

True or false, the N terminus is highly conserved

Answer 11

False, this is very distinct because different microbes interact with different chemicals
C terminus is conserved because the chemotaxis system is same typically

Question 12

What Are MCP’s? list all.

Answer 12

• 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

Question 13

True or false, MCP’s measure the concentration of chemicals in the environment and then send signals to chemotaxis system.

Answer 13

False, they only detect changes in concentration

Question 14

Name the attractants and repellents Tar can detect.

Answer 14

A: Maltose and aspartate
R: Nickel and cobalt

Question 15

Explain the signal transduction chemotaxis system up until CheA!!

Answer 15

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

Question 16

When does CheA autophosphorylation increase?

Answer 16

when attractant decreases or repellent increases! Think, if attractant is decreasing then the cell needs to change direction. To change direction CheA must phosphorylate

Question 17

When does CheA autophosphorylation decrease?

Answer 17

If A is increasing or R is decreasing

Question 18

Explain the process if the the cell is in an environment with decreasing attractant

Answer 18

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)

Question 19

When is CheY not phosphorylated and why?

Answer 19

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.

Question 20

What are CheB and CheR?

Answer 20

Co-factors for the chemotaxis system
CheB is methylase
CheR is methylesterase

Question 21

Explain the concept of a two component regulatory system

Answer 21

• very common
• one component is a histidine kinase
• one component is a response regulator
• There is phosphate transfer between them

Question 22

In the chemotaxis system, what is the histidine kinase and what is the response regulator?

Answer 22

CheA is the kinase

CheY is the regulator

Question 23

Explain chemotaxis adaptation? explain how MCP’s produce a signal for the cell to know what the environment is like.

Answer 23

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

Question 24

comparing methylation levels of MCP’s tells the cell what?

Answer 24

comparing previous and current methylation levels of MCP’s can tell the cell whether concentration is going up or down.