Mitosis and Microtubules

Question 1

At the kinetochore what are motor proteins involved in?

Answer 1

Capturing microtubules and sensing tensions

Question 2

Are most microtubule motors involved in mitosis plus or minus end directed?

Answer 2

Plus

Question 3

What do microtubule motors carry in mitosis?

Answer 3

• Chromosomes
• Signalling factors
• Microtubules

Question 4

What does kinesin-5 do?

Answer 4

Causes centrosomes to move further apart

Question 5

What does the overlap of microtubules on chromosomes help?

Answer 5

To push centrosome into correct position

Question 6

What is the spindle self assembly model?

Answer 6

• Does not require centrosomes or kinetochores
• Chromatin mediated
• Chromosomes have an affinity for microtubules and drives polymerisation

Question 7

What experiments showed DNA is sufficient to drive spindle assembly?

Answer 7

Magnetic beads were coated in DNA and mitotic frog extract and overtime get formation of mitotic spindles

Question 8

What regulates the activity of BimC?

Answer 8

Cyclin B and Aurora A

Question 9

In prophase what drives centrosome separation?

Answer 9

Anti-parallel microtubule sliding

Question 10

In prophase what co-ordinates centrosome separation?

Answer 10

BimC

Question 11

What effect do Cyclin B and Aurora A have on BimC?

Answer 11

They phosphorylate and activate it

Question 12

What happens to the nuclear envelope in prometaphase?

Answer 12

It breaks down

Question 13

What supports bipolar attachment of microtubules to kinetochores in prometaphase?

Answer 13

CENP-E

Question 14

What does CENP-E do?

Answer 14

• Helps to capture and stabilise mt
• Important for the recruitment of BubR1 in spindle assembly checkpoint

Question 15

what happens chromosomes in metaphase?

Answer 15

All chromosomes are connected by both spindle poles in kinetochore-associted mt

Question 16

What happens in metaphase when the tension across the kinetochore is balanced?

Answer 16

Cell senses it and relieves spindle assembly checkpoint and activates APC/cdc20

Question 17

What does the APC/Cdc20 complex do?

Answer 17

Breaks down cohesins

Question 18

How does APC/Cdc20 cause the breakdown if cohesin?

Answer 18

• Securin binds to protease separase, keeping it in an inactive state
• APC/cdc20 ubiquitinates securin so it is broken down

Question 19

What prevents the transition from metaphase to anaphase?

Answer 19

• Misaligned chromosomes

Question 20

What is the role of MCAK in anaphase A?

Answer 20

• Potent microtubule depolymerising agent
• Reduces length of kinetochore
• So contributes to poleward movement

Question 21

What is the role of cytoplasmic dynein in anaphase A?

Answer 21

• May translocate towards the spindle poles due to negative directed effect
• Pulls kinetochore along MT surface

Question 22

What is the role of cytoplasmic dynein in anaphase B?

Answer 22

Pulls astral microtubules, thereby pulling the centrosomes apart

Question 23

What does kinesin-5 do in anaphase B?

Answer 23

Cross-link microtubules in the midzone, sliding them apart

Question 24

What motors are important for cytokinesis?

Answer 24

Kinesin 6/MKLP

Question 25

What are motors useful for in cytokinesis?

Answer 25

organise midzone MT and regulate interactions with cortex

Question 26

What does MKLP2 do in cytokineses?

Answer 26

• Involved in recruiting signalling proteins which are phosphorylated by polo-like K1 and then act as a platform to recruit polo

Question 27

What does MKLP 1 do in cytokinesis?

Answer 27

Forms central spindilin complex which regulates RhoA GTPase, positions signalling factors to regulate actin cytoskeleton