Lecture 13 Flashcards
Kinetochore MTs
MTs ahve to fina dna ttach to the kinetochores - they must be able to undego co-ordinated assembly and disassembly
Interpolar MTs
MTs gorwing from one pole must meet those from the other pole and form anti-parallel interactions
Prophase general summary (What do chromosomes do, and why?)
chromosomes condense in prohpase - condensins compact the DNA
Duplicated ____ start to separate in prophase - needs the ____ here, where MTs overlap
centrosomes
kinesin Eg5
Centrosomes ________ in prohpase
nucleate more MTs `
Where do the mitotic spindles start to form?
the interpolar MTs
THe _______________ disassembles, allowing ___________ to interact with chromosomes
nuclear envelope
microtubules
Growing and shrinking MTs contact the ____________ on the chromosome
kinetochores
In metaphase, chromosomes attach to _____________ by _________________ with one kinetochore attached to each pole
spindle
kinetochores
Transition from metaphase to anaphase is blocked if:
- microtubules ___________
- microtubules ___________
- the __________ hasn’t assembled properly
depolymerized
stabilized
spindle
Transition from metaphase to anaphase is also blocked if a _____________________ is not attached to the spindle
single kinetochore
a _________ needed for metaphase checkpoint
protein kinase
How is anaphase delayed if chromosomes are unaligned
kinetochores are unattached, and the stop signal is generated by the spindle assembly checkpoint complex (SAC) at the kinetochore and anaphase is delayed
how does transition to anaphase happen when chromosomes are aligned?
kinetochores are attached
SAC proteins removed from KTs by cytoplasmic dynein
no stop signal
all clear for anaphase
The active SAC complex at the kinetochore activates a cystosolic pool of _____ inhibitor complex
APC
what does APC stand for?
anaphase promoting complex
what does APC do?
- triggers proteolysis of specific proteins
- covalently attached ubiquitin (small protein)
- ubiquitin tagging directs proteins to the proteasome for degradation
what does inhibiting Mad2 result in?
cytokinesis without anaphase even if MTs are absent
how do sister chromatids separate?
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)
What happens in the two phases of anaphase?
A: sister chromatids move towards the spindle poles
B: spindle poles move further apart
In anaphase A, sister chromatids move towards poles by staying attached to ____________
depolymerizing kinetochore MTs
in anaphase B, spindle poles move further apart via what?
- pushing outwards at centre of spindle (eg5)
- interpolar MTs continue growing - get longer
(also dynein anchored in the cell cortex pulls on astral MTs)
