lecture 11 Flashcards
what needs to happen for cell division
microtubules rearrange, form mitotic spindle machine, evenly split genetic info
step 1 of cell cycle
grows; needs more of everything, including DNA/chromosomes, b/c it’s splitting
step 2 of cell cycle
after growth/synthesis phase, cell undergoes split of chromosomes into daughter cells (chromosome segregation)
step 3 of cell cycle
actual cell division; split into 2/cytokinesis
S phase
synthesis; cells need to grow and duplicate DNA
M phase
mitosis; split chromosomes evenly among daughter cells, includes cytokinesis
interphase
cell doesn’t seem to do anything, but it’s actually undergoing S phase
M phase
prophase, prometaphase, metaphase, anaphase, telophase
phases in interphase
G1, S, G2
what controls transitions b/w phases
checkpoints; is everything okay? ex. are all chromosomes attached to mitotic spindle (metaphase to anaphase)
what controls timing b/w phases of cell cycle
these checkpoints
reg. protein complex that controls when cells go from one phase to another
cyclin-dependent kinase complex
what specifically controls diff transitions of cell cycle
kinase activity
what happens when checkpoints are satisfied
signals activate CDK, phosphorylate downstream targets to initiate next phase
what needs to be bound to complex for it to be active
cyclin
what happens if no cyclin
kinase is inactive
what controls CDK activity to allow transition from one phase to another
expression of cyclin
what happens as you go thru cell cycle
cyclin expression goes up and down
describe CDK expression
constant
when is CDK active
when cyclin is bound
describe CDK thru cell cycle
expression doesn’t change, but activity changes based on cyclin [ ]
what is cyclin for M-CDK
cyclin B or cyclin M
what does cyclin B/M do
controls M-CDK activity
what is checkpoint for metaphase to anaphase pathway
are chromosomes successfully attached to mitotic spindle
what happens if not attached
protein complex inhibited, chromosomes CANNOT segregate
what happens if not inhibited
M-CDK activity is controlled, cells progress further into cell cycle
what needs to happen to cyclin to go from metaphase to anaphase
M-cyclin needs to be degraded, turn off M-CDK activity
describe mechanism for degradation of M-cyclin
chromosomes attached to spindle –> activates cdc20 –> binds to APC –> APC/cdc20 complex –> ubiquitilates M-cyclin and adds polyubiquitin chain, targets it for degradation by proteasome
prophase
2 centrosomes (have duplicated), DNA condensed into chromosomes, nuclear envelope intact (chromosomes r in it)
prometaphase
breakdown of nuclear envelope, chromosomes free to swirl around, centrosomes at opposite ends of cells, kinetochore
metaphase
chromosomes attached to mitotic spindle at center
anaphase
chromosomes separating, moved to opposite poles of cell
telophase
right before cytokinesis; 2 centrioles in opposite poles, 2 nuclear envelopes reform
cytokinesis
nuclear envelope fully formed, chromosomes decondense, actively being split
what happens to trigger anaphase
as long as chromosomes attached (even if 3 instead of 2)
mitotic spindle
built out of microtubules; radiate out of centrosome
3 types of MTs
kinetochore microtubules, non-kinetochore microtubules, astral microtubules
kinetochore microtubules
extend toward midpoint of cells (From ends), chromosomes attach here to satifsy metaphase to anaphase checkpoint
non-kinetochore
extend toward midpoint, but smaller chunks; help position mitotic spindle
astral microtubules
radiate away from midpoint; other drxn, at ends; help hold mitotic spindle in orientation
individual motor proteins
kinesins 4&10, kinesin 5, dynein
kinesins 4/10
walk chromosomes to midpoint, plus ends of kinetochore microtubules (get chromosomes to right spot)
kinesin 5
4 motor domains, walks along 2 MTs; pushes apart poles by walking to plus ends (both are in opposite drxns)
inhibit kinesin 5?
poles would come closer together
kinesin 14
one set of motor domains, other binds to MT and carriers it as cargo; walks to minus end –> pulls poles closer together
dynein
one part binds plasma membrane, walks toward minus end; pulls centrosome to plasma membrane to keep it anchored (astral MTs)
what balances forces
dynein, kinesin 5, 14
when is the idea of balancing dynamic forces needed
metaphase to anaphase transition; not needed after cuz mitotic spindle not needed
how are chromosomes attached to kinetochores
plus ends bind perpendicular
what is only stable kinetochore conformation
one side bound to one chromosome, other side bound to other chromosome
cdc20 separase pathway
apc/cdc20 complex, ubiquitinates securin & destroys it, activates separase( Protease) that targets cohesins, degrades it, separating daughter chromosomes
what happens when chromosomes are not attachedq
MAD20 is active
what does MAD20 do
inhibits cdc20
