Motility

Question 1

4 Key elements of Taxis

Answer 1

1. Sense external signal
2. Transduce into internal signal
3. Alter behavior
4. Adapt to a range of stimulus

Question 2

E.coli Motility

Answer 2

• random walk: no stimulus present
• biased random walk: as attractant concentration increases, e.coli runs longer in direction of attractant and tumbles less frequently
• e.coli sense temporal gradient

Question 3

4 Flagellar arrangements

Answer 3

1. monotrichous (one on one side)
2. amphitrichous (one on each side)
3. lophotrichous (multiple on one side)
4. peritrichous (multiple all around)

Question 4

Microscopes that visualize flagella

Answer 4

• stains/fluorescence
• dark field (sunlight illuminating dust)
• EM (not good for living cells)

Question 5

How does flagella induce motility: whip model or propeller model?

Answer 5

• whip model: beating side to side
• propeller model: spinning
• mutant assay: : mutagenized flagella and isolated mutants -> found that when stimulated mutants stuck to a glass slide spun (propeller motion is reality)

Question 6

How does CCW or CW spin drive run and tumble?

Answer 6

• CCW = run -> flagella bundles
• CW = tumble -> flagella is apart

Question 7

Che Pathway

Answer 7

• CheY -> CCW (run)
• When CheA (kinase) interacts with CheY, it is phosphorylated -> CW (tumble)
• When CheZ (phosphorylase) interacts with CheY-Pi, it is dephosphorylated -> CCW (run)

Question 8

How is flagellar rotation regulated (Che Pathway +/- attractant)?

Answer 8

• adding attractant inhibits CheA, promoting CheY function
• absence of attractant allow CheA to function, and equilibrium between CheY and CheY - Pi occurs

Question 9

How is the flagella provided power?

Answer 9

• similar to ATP synthase
• H+ are moved from the outside to the inside of the organism by a motor protein -> turns electrochemical energy into mechanical energy (proton motive force)

Question 10

3 Non-flagellar motility

Answer 10

1. twitching motility: pilus polymerizes, attaches to surface, and depolymerizes to pull bacteria forward (grappling hook)
2. gliding motility: slime extrusion and needs surface
3. actin-based motility: actin polymerizes to push the front of the bacteria forward on surface, depolymerization retracts back of bacteria and needs surface

Question 11

2 cytoskeletal filaments for motility

Answer 11

1. microtubules (made of tubulin)
2. actin (made of actin)

• regulated by accessory proteins that link to each other and cell components, assembly and disassemble, and intitate movement

Question 12

What is “treadmilling” (actin)?

Answer 12

• actin is added to positive end which pushes membrane forward
• actin on negative end is broken down and recycled
• acts as a treadmill

Question 13

What organisms do actin based motility?

Answer 13

• entamoeba histolytica
• naegleria folweri

Question 14

3 cytoskeletal motors

Answer 14

1. kinesin moves to + end of microtubules
2. dynein moves to - end of microtubules
3. myosin moves on actin

• uses ATP hydrolysis to power movement

Question 15

Eukaryotic flagella

Answer 15

• made of 9+2 arrangement of microtubules
• surrounded by **cell membrance **(versus bacteria flagella which just sticks out)
• green alga and protozoan
• observed through high-speed video microscopy

Question 16

How do eukaryotic flagella beat? What proteins are involved?

Answer 16

• sliding filament model: dyneins slide two microtubules and nexin cross-link holds the two microtubles so that sliding becomes bending
• to test this: used protease to remove cross-links and found that without the cross links no bending occured and MT would slide apart

Question 17

Non-flagellar motility in eukaryotes

Answer 17

• gliding motility in toxoplasma
• membrane rolls on surface like the wheels on a tank
• depends on actin and myosin