mitotic spindle Flashcards
At what phase does Centrosome duplication occurs?
G2
At what phase does Mitotic spindle formation occurs?
prophase
At what phase does Chromosome condensation occurs?
prophase
At what phase does Breakdown of nuclear envelope occurs?
prometaphase
At what phase does Chromosome attachment to MTs begins?
prometaphase
How do M-Cdk induce dynamic changes in MT?
decrease MAP activity by phosphorilation
increase Kinesin activity by phosphorylation
leading to an increase in dynamic changes in MT
Name and describe the components of the mitotic spindle
- Microtubules
- Astral
- Kinetochore
- Overlap
- Motor proteins
- Kinesin-related (+)
- Dynein (-)
- Allow expention of mitotic spindle
- Destabilise MT
3.Chromosomes (chromatids)
•The cargo
4.Centrosome (devide and start process)
- Centrioles
- PCM: help to nucleate and form – end of MT
Fill in the blank
How do + directed Multimeric motor proteins Contribute to Spindle Assembly?
- Multimeric motor proteins “cross-link” antiparallel MTs.
- (+) end-directed kinesin-related proteins (KRPs, e.g. BimC or kinesin-5).
- KRPs self-associate with each other at their tail domains.
- Slide overlap MTs past each other.
- Promotes elongation of mitotic spindle.
both – and + end MT are free and dynamic (not restricted by other structure) important bc they have to be able to loose and gain subunits
How do - directed Multimeric motor proteins Contribute to Spindle Assembly?
dyneins and kinesin-13 do the same as kinisine but other direction and create foci at spindle poles, therefore stabilising MT
both – and + end MT are free and dynamic (not restricted by other structure) important bc they have to be able to loose and gain subunits
How does the spindle pole seperation (elongation) occurs ?
- DuringProphase
- KRPs push overlap MTs.
- Dyneins pull astral MTs.
How does chromosomes seperation occurs?
APC-cdc25 ubiquitinate Cohesine so that most cohesin is replaced by condensin during prophase.
Cohesin and condensin have similar ATP and DNA-binding domains.
Condensation dependent on ATP hydrolysis and phosphorylation of condensin by M-Cdk.
- Condensine shorten overall structure
- Cahesine pack DNA tightly
how does the kinetochore attachement happens?
Occurs during prometaphase. The astral MT attaches to the kinetochore which in turn, increases the stability of the MT. This bipolar attachement transforms astral MT in kinetochore MT.
Mecanism:
+ end attaches to the kinetochore. It does so by being centered onto it by motor proteins (KRP, CENP-E, dynein). This is important because if the MT touches the fibrous corona (fiber allowing attachement) during attachement, the MT will distabilise.
This will happens on both side and you have a push (the astral ejection force) (KID protein) and pull (MTor) effect from the motor protein that creates enough stability for the creation of the metaphase plate. The metaphase plate is also created because the distance between MT and kinetochore can be changed and that allows allignment of chromosomes
Describe the poleward flux
Another way to balance at the metaphase plate that does not involve molecular motors
Turnover of MT polymerisation will end up in balance and bring the chromosome in the middle
Explain the seperation of chromatides during anaphase A
Anaphase A:
- Kinetochore MT looses tubuline at the + end because of KRP, , driving chromatide at the poles (poleward mouvement). There’s also a continual loss at the - end. (Kinesin-13 depolymerizes at both ends by pulling MT appart)
- NDC 80 acts like the corona fibers, they will destabilise MT
- Dam1 ring maintains attachment between MT and chromatid. It harnesses the energy of GTP hydrolisis to promote mouvement
Explain the seperation of chromatides during anaphase B
Anaphase B
- Pulling by Dyneins at poles: anchored to cell cortex pull themselves toward (-) end of astral MTs.
- Pushing by KRPs at central spindle: cross-link and push overlap MTs apart.
- Further elongation of spindle.
