cell cycle 3 & 4: molecular control & checkpoints

Question 1

what are the different ways by which aneuploidy can arise?

Answer 1

monotelic attachment: chromatid only attached to one centrosome
syntelic attachment: chromatid only attached to one centrosome via two microtubules
merotelic attachment: chromatid attached to both centrosomes via both sides of kinetochore

Question 2

what is the spindle assembly checkpoint?

Answer 2

senses completion of the chromosome alignment in the middle
- occurs between prometaphase & metaphase

Question 3

what happens during the spindle assembly checkpoint?

Answer 3

BUB protein kinases dissociate from kinetochores when attached to the spindle & CENP-E (centromere protein E) checks that all the chormosomes are connected to it

Question 4

how can anti-cancer therapies induce chromosome missegregations?

Answer 4

inhibition of BUB protein kinases -> cell doesn’t pass M checkpoint
- inhibition of attachment error-correction mechanism -> segregation is faulty

Question 5

how can tumours affect the cell cycle?

Answer 5

increase the levels of growth factors -> sends more cells out of G0 into cell cycle

• can break the G2 checkpoint & M checkpoint -> every cell enters mitosis despite errors
• can stop cells leaving cycle into G0 after mitosis forcing more mitosis

Question 6

what happens if something goes wrong during the cell cycle?

Answer 6

if cell isn’t big enough or there is DNA damage:
apoptosis (if damage is too great to be repaired)
temporary cell cycle arrest at a checkpoint (until problem can be rectified)