Mitosis Phase Flashcards
What is stopped from getting degraded in the spindle assembly checkpoint
Cyclin b and securin (allowing anaphase)
Which m cyclin is nuclear and which moves to nucleus from cytoplasm
Nuclear is a
Cytoplasmic is b
When does cyclin a get degraded
Before prometaphase
When does cyclin b increase / peak and then lower
Peak is at prometaphase
Low is met- anaphase
What is the main cdc25 for cdk1 cyclin b activation by removal of wee1/myt1 phos
Cdc25b
What kinase is a target of the active cdk1 and cyclin b which causes a positive feedback loop for more activation
Polo like kinase
What does plk do in respect to cdk 1 activation
Phos of wee and myt inhibiting them
Also phos of cdc25a, and c as well as b which all cause cdk activation
How can cyclin a aswell as main cdc25b be a trigger for mitosis via cdk1 activation
When in complex with cdk it allows aurora a activation of plk
Plk then causes a loop via phos of cdc25c
How many centrioles are from centrosomes
2
Explain centrosome cycle which duplicates for mitosis
In g1 centrosome pulls apart but held by procentrioles
Centrosome is duplicated in s phase
Centrosome disjunction through pulling of procentrioles in s/g2
Full centrosome separation in mitosis and bipolar spindle formation
What is pulling apart of procentrioles called in g2 and what kinase involved
Centrosome maturation via plk4
Other than activating cdk1 cyclin b and plk for centrosome maturation, what do plk do
Prophase pathway of cohesin ring removal on sister chromatid arms
Cytokinesis in the actin myosin ring
What is aurora a for
Spindle integrity
What is aurora b part of
Cpc chromosome passenger complex
With incenp, survivin, borealin
Where is aurora b and why
Chr arms early eg in mitosis
Moves to centromeres in prometaphase this is so it can aid correct attachment of kinetochores with mt
Via phos of kmn proteins
What spindle attachment is when 1 attaches to each sister
Amphitelic
Does amphitelic produce a sac and why
No sac is inactive because equal tension
What is monotelic
When only 1 sister is attached
Produces active sac bc no tension so aurora b present
What is syntelic
When both mt attach to one sister
Also produces active sac as no tension
What is merotelic and why doesn’t this have active sac
Both arms attached but 1 has more mt attached
Tension but unequal
Which enzyme opposes aurora B action via dephosphorylation
Pp1
When does pp1 get replaced by aurora b
Prophase when aurora b on chr arms
What inhibits pp1
i2 inhibitor
What happens when aurora b moves from arms to centromeres in prometaphase
Part of sac
It checks tension. If not there aurora b will cause kinetochore assembly and phos kmn proteins causing proper attachment of k with mt
When this happens anaphase can occur
Aurora b stays in middle of cell and far from kinetochore, allowing kinetochore dissassembly and pp1 increase via i2 degradation from anaphase
What is the strong interaction with merotelic and aurora b
Because stay in middle, aurora b can phos of kinetochore subunits and allow proper attachment
What does sac block which blocks progression to anaphase
Apc/cdc20
What does securin ub do and how does it allow anaphase
Securin degradation activates separase which cleaves cohesin rings around the centromeres = separation
Cyclin b causes cdk inactivation and therefore dephos of its substrates , how does this allow anaphase
Spindle elongation and allows chr separation to poles
How is cdk 1 inactivation good for telophase and mitotic exit
Nuclear formation and spindle dissassembly
What part of sac blocks apc cdc20
Mitotic checkpoint complex mcc
What are the key components of mcc
Mad 2 closed, bubr1, bub3
What does mad2 closed binding to cdc20 do
Blocks it’s ability to recognise and degrade cyclin b and securin
How are cyclins usually recognised by cdc20
N terminal destruction d box
Arg and leucine residues
What part of apc also recognises substrates
Apc10
What occurs for mcc activation
Mps1 phosphorylates KNL1
Allows rzz and other binding like bubr1 and bub3
Rzz recruits mad1 and 2
Mad 2 put into a closed complex which binds cdc20
Attracts others like bubr1 and bub3
How does physical separation silence the sac
Aurora B once phos kmn will allow proper kinetochore attachment
When tension anaphase occurs
Aurora B moves away from kinetochores and stays in middle, allowing pp1 then to dephos and disassemble kinetochores
This silences the sac
How does p31 comet silence sac by disrupting mcc
Competes with bubr1 for mad2 binding
What phosphorylates cdc20 to cause mcc dissassembly and sac turn off
Cdk1
What is the cdc20 ub dependant path
Cdc20 can be degraded via p31 comet ub
Allows mcc fall off and new cdc20 production without silencing
What can dephos knl1 platform protein which blocks mcc assembly
Pp2a phosphatase
How is cyclin a degraded even though sac is turned on in prometaphase nuclear degradation
Apc cdc20 can override the sac at this point via long D boxes of cyclin a being recognised
What is degraded by cdh1 apc (end of mitosis)
Cdc20 , plk, aurora a and b
