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what percentage of cells are in G0 phase
99.999% of cells
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do all species control the cell cycle the same way
nope
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how does cell cycle start off
origin of replication, triggers replication of replicon near it
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when is each origin licenesed
during interphase
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when does pre-replication complex break down
when replication starts
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what happens in G1 phase
- where cells are born
- physical growth stay in cell cycle or exit to GO
- contains a restriction point
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for what reasons would a cell not pass the first restriction point
if starved, external signals, or inhibitory signals
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G0 phase
most cells in the body are in G0 phase
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what happens in S phase
- each licensed origin fire simultaneously
- triggered by kinases, takes minutes
- pre-RC dismantles and is not rebuilt again until G1
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how long is one replicon
~3,000 bases
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how are sister chromatids linked together
cohesin proteins, only releases during mitosis
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what happens in G2 phase
- very brief, quickest, part of the cell cycle
- cells start to accumulate chemical signals to activate mitosis (cyclins)
- contains second restriction checkpoint
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cytoplasmisis
physical separation of cytoplasm cut in half
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parts of mitosis
- prophase
- prometaphase
- metaphase
- anaphase
- telophase
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what happens in prophase
- chromatin folds up into loops and condenser-cohesins hold them together
- cytoskeleton rearrangements
- dynamic instability
- centrosomes duplicate and divide
- centrioles and pericentriolar material nucleates MTs
- forms mitotic spindle poles
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what happens in prometaphase
- nucelar envelope dissolves due to increased cyclin/cdks
- kinetochores of chromosomes bind (+) end of MTs
- unattached kinetechores give signals that inhibit mitosis
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what happens in metaphase
brief moment when chromosomes are perfectly lined up
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what happens in anaphase
sister chromatids release each other-triggered by phosphorylation and proteases that cut cohesins
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anaphase A vs. B
- A-MTs move toward the poles
- B-poles move themselves toward the end of the cell
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what happens in telophase
chromatin ends up on opposite side of the cell and nucleus reforms
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what controls cell cycle
kinases(only active when bound to cyclins)
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what always exist at the same concentration
cdks
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main cdk responsible for G1 restriction point
cdk2
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main cdk responsible for G2-metaphase transition and M phase
cdk1
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how are cyclins regulated
by transcription and translation
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What cyclin is at its peak at the beginning of Mphase
A
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What cyclin is at its peak at the beginning of anaphase
B
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What cyclin is at its peak at G1/S
E
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how are cdks regulated
phosphorylation and cyclin activating kinases
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things that cdk1 PO in prophase
- lamins-N.E
- LIS-I, NDE- increase affinity for dyneins that rip-off chuckcs of N.E
- GRASP65-results in reduced golgi stacking
- COPI-allows golgi vessicles to form but it can't re-fuse
- COPII-prevent ER-golgi trafficking
- histone H1-creates higher affinity for self assembly
- kinesin5-causes it to walk toward + end and push MTs and centrioles apart
- MAPS-dissociate from MTs, result in distabilization(dynamic instability)
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3 classes of MTs
- Astral Mts-points toward back of the cell
- polar overlap-MTOC and toward each other
- kinetochore
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function/structure of PO kinesin5
- bipolar kinesin (2 molecules)
- bind to two opposite direction MTs and push them against each other to opposing poles
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what modulates chromatin condensation
cohesins and condensins
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