L20- Mechanics of cell division 2 Flashcards
What does the metaphase checkpoint check?
- chromosomes attached to the spindle by both kinetochores
- chromosomes align in middle of spindle
- kinetochores are under tension attached to MTs
What does the metaphase checkpoint control?
The transition from metaphase to anaphase
What triggers the exit from metaphase and entry into anaphase?
The degradation of cyclin. This is tightly controlled and activated in metaphase. Caused by APC.
WHat degrades cyclin, causing entry into anaphase?
The anaphase promoting complex (APC)
What are the 3 reasons why transitions from metaphase to anaphase would be blocked?
- microtubules are depolymerised (nocodazole)
- microtubules stabilized (taxoll)
- spindle hadn;t assembled properly (monastrol inhibiting Eg5)
What is Mad 2?
Mad2=protein kinase needed for the metaphase checkpoint. Blocking Mad2 causes cytokenesis without anaphase even if MTs are absent.
Mad2 tells the cell to wait before dividing.
If the chromosomes were unaligned what would Mad 2 do?
Generate a negative signal-> delaying anaphase
When do sister chromatids stick together until?
Anaphase, when they separate abruptly.
How do sister chromatids separate?
Cohesins are cleaved by a protease called separase.
This triggers start of anaphase.
What does APC do?
Triggers degradation of cyclin by the proteosome.
controls cyclin degradation
How do sister chromatids move towards the poles?
Via kinetochore-MT depolymerisation. The MT disassembles and the kinetochore follows
How do the spindle poles move further apart?
- Pushing outwards at centre of spindle by Eg5.
- Dynein in cell cortex pulls on astral MTs
- Polar MTs continue growing, overlap zone gets smaller (not quite sure what that means?)
What does Eg5 do?
Pushes the poles apart
Where does dynein pull MTs to?
Towards the plasma membrane
What are the events in telophase?
Nuclear envelope reassembles
Golgi reassembles
Secretion and endocytosis restart
(the genome has separated but the cytoplasm hasn’t)
