Microtubule Function

Question 1

Motor proteins require __

Answer 1

ATP

Question 2

Axonal Transport

Answer 2

Squid Axons (model system)

• radioactive aa injected
• proteins move along MT
• SDS-PAGE

labelled proteins travel at different speeds in cell

Question 3

Kinesin

Answer 3

MT (+) end directed motor protein

• 2 heavy chains = head, neck, stalk (ATPase and MT binding)
• 2 light chains = recognize cargo

Question 4

Functions of Kinesin

Answer 4

Organelle Transport

• Kinesin-1 = 2 heavy + 2 light
• Kinesin-2 = 2 heavy (heterotrimeric)

Sliding
- Kinesin-5 = 4 heavy (bipolar)

Disassembly
- Kinesin-13 = 2 heavy – head+neck

Question 5

Cargo Movement

Answer 5

• cargo need appropriate receptor that is recognized by specific light chain

Question 6

Movement of Kinesin

Answer 6

• anterograde
• kinesin btwn αβ dimer
• ATP hydrolysis –> kinesin has conformational change (head moves 16nm)
• linker swing forward + dock head = power stroke

Question 7

Cytoplasmic Dynein

Answer 7

MT (-) end directed motor protein

• heavy chains = ATPase activity + stalk
• linker interact with dynactin complex – bind cargo
• ATP hydrolysis = drive movement

Question 8

Dynactin Complex

Answer 8

• links dynein to cargo
• regulated by dynamitin (release cargo)
• p150glued binds MTs

Question 9

Post-translational Modification of Tubulin

Answer 9

• acetylation of a lysine residue of α tubulin

- stabilize MT

Question 10

Cilia vs Flagella

Answer 10

Cilia = 2-10μm
Flagella = 10-2000μm

Question 11

Axoneme

Answer 11

• 9+2 array of microtubules
• outer doublets — A and B tubules held with nexin
• axonemal dynein (stem - A tubule) (head reach to B tubule)

Question 12

Axoneme and Basal Body

Answer 12

• 9 basal body triplet MTs

- A and B tubule pass transition zone. C tubule does not

Question 13

Axoneme Bending

Answer 13

• sliding MT against each other
• NO nexin = dynein moves to (-) end + MTs slide
• Nexin = bending + no sliding

Question 14

Intraflagellar Transport

Answer 14

• moves material “up and down”

- uses cytoplasmic dynein

Question 15

Interphase Cells

Answer 15

Contain a non-motile primary cilium

• axonemal structure
• no axonemal dynein

Question 16

Karyokinesis vs Cytokinesis

Answer 16

• karyokinesis = divide chromosomes

- cytokinesis = divide cytoplasm

Question 17

MT Phases of Cell Cycle

Answer 17

Interphase = centrosome duplication
Prophase = mitotic aster separation
Metaphase = chromosomes aligned at metaphase plate
Anaphase A = chromosome move to poles
Anaphase B = spindle pole separation
Telophase = contractile ring
Cytokinesis = interphase MT array + cleavage furrow

Question 18

Microtubule Stability Cell Cycle

Answer 18

Interphase – stable

Mitosis – unstable

• XMAP215 inhibited by phosphorylation
• kinesin-13 depolymerizes

Interphase – stable
- XMAP215 enchanes polymerize at (+) end

Question 19

Components of Mitotic Apparatus

Answer 19

Polar MTs – microtubules grow to other pole
Kinetochore MTs – microtubules attach to chromosomes
Astral MTs – microtubules grow away from pole

Centrosome –> Mitotic Apparatus

Question 20

Centromere

Answer 20

• attachment site for MT

- kinetochore proteins capture daughter chromosomes from each side

Question 21

Spindle Formation

Answer 21

Polymerize + Depolymerize bring chromosome to center

• kinesin = (+) end motor protein PUSH away from pole
• dynein = (-) end motor protein PULL toward pole
• kinesin-13 = depolymerization

Question 22

Capturing Chromosomes

Answer 22

• Ndc80 holds MT (tension = bi-orientation)

No Tension – only 1 MT attach

• Aurora B phosphorylates Ndc80 proteins
• Ndc80 lets go

Tension

• Aurora B does not phosphorylate Ndc80 proteins
• Ndc80 proteins bound to MT

Question 23

Cortical Anchor Activity

Answer 23

• inactive = no movement

- active = dynamin and dynactin pull spindle in the direction

Question 24

Anaphase A

Answer 24

• kinetochore MT shortening (chromosome –> pole)

- depolymerization by kinesin-13

Question 25

Anaphase B

Answer 25

- motors (pole separation) - Polar MTs slide by kinesin-5 - Astral MTs pulled by anchored dynein

Question 26

Locate Cytokinesis Origin

Answer 26

- Polar MTs localize RhoGTP | - formation of contractile ring at old metaphase plate