Lecture 13

Question 1

Kinetochore MTs

Answer 1

MTs ahve to fina dna ttach to the kinetochores - they must be able to undego co-ordinated assembly and disassembly

Question 2

Interpolar MTs

Answer 2

MTs gorwing from one pole must meet those from the other pole and form anti-parallel interactions

Question 3

Prophase general summary (What do chromosomes do, and why?)

Answer 3

chromosomes condense in prohpase - condensins compact the DNA

Question 4

Duplicated ____ start to separate in prophase - needs the ____ here, where MTs overlap

Answer 4

centrosomes
kinesin Eg5

Question 5

Centrosomes ________ in prohpase

Answer 5

nucleate more MTs `

Question 6

Where do the mitotic spindles start to form?

Answer 6

the interpolar MTs

Question 7

THe _______________ disassembles, allowing ___________ to interact with chromosomes

Answer 7

nuclear envelope
microtubules

Question 8

Growing and shrinking MTs contact the ____________ on the chromosome

Answer 8

kinetochores

Question 9

In metaphase, chromosomes attach to _____________ by _________________ with one kinetochore attached to each pole

Answer 9

spindle
kinetochores

Question 10

Transition from metaphase to anaphase is blocked if:
- microtubules ___________
- microtubules ___________
- the __________ hasn’t assembled properly

Answer 10

depolymerized
stabilized
spindle

Question 11

Transition from metaphase to anaphase is also blocked if a _____________________ is not attached to the spindle

Answer 11

single kinetochore

Question 12

a _________ needed for metaphase checkpoint

Answer 12

protein kinase

Question 13

How is anaphase delayed if chromosomes are unaligned

Answer 13

kinetochores are unattached, and the stop signal is generated by the spindle assembly checkpoint complex (SAC) at the kinetochore and anaphase is delayed

Question 14

how does transition to anaphase happen when chromosomes are aligned?

Answer 14

kinetochores are attached
SAC proteins removed from KTs by cytoplasmic dynein
no stop signal
all clear for anaphase

Question 15

The active SAC complex at the kinetochore activates a cystosolic pool of _____ inhibitor complex

Answer 15

APC

Question 16

what does APC stand for?

Answer 16

anaphase promoting complex

Question 17

what does APC do?

Answer 17

• triggers proteolysis of specific proteins
• covalently attached ubiquitin (small protein)
• ubiquitin tagging directs proteins to the proteasome for degradation

Question 18

what does inhibiting Mad2 result in?

Answer 18

cytokinesis without anaphase even if MTs are absent

Question 19

how do sister chromatids separate?

Answer 19

cohesins are cleaved by a protease called separase
separase is tightly controlled - and is activated in metaphase - triggering start of anaphase (only happens when SAC is inactivated)

Question 20

What happens in the two phases of anaphase?

Answer 20

A: sister chromatids move towards the spindle poles
B: spindle poles move further apart

Question 21

In anaphase A, sister chromatids move towards poles by staying attached to ____________

Answer 21

depolymerizing kinetochore MTs

Question 22

in anaphase B, spindle poles move further apart via what?

Answer 22

• pushing outwards at centre of spindle (eg5)
• interpolar MTs continue growing - get longer
  (also dynein anchored in the cell cortex pulls on astral MTs)