Mitosis and Cytokinesis - Bi Flashcards
How does a branched network of actin filaments get formed in the example of a neutrophil chasing a bacteria?
chemoattractant –> receptor and trimeric G protein –> small G protein (CDC42/Rac) –> WASP/Wave –> Arp2/3 –> dynamic actin –> cell migration
How long is mitosis ? how long is cytokinesis?
Mitosis is an hour. Cytokinesis is 20 minutes.
Constant across most cell types, G1 is what varies.
What 2 things have morphologies that we are interested in during cell division cycle?
- spindle
- chromosome
Three types of microtubules associated with the spindle?
- Astral microtubules
- Kinetochore microtubules: attach to chromosome
- Interpolar microtubules: Microtubules that come from both poles and interdigitate.
Which direction are microtubules pointing?
Plus ends point outward, minus ends are toward the spindle pole.
MTOC
Microtubule organizing center - the centrosomes.
How are centrosomes duplicated?
In a semi-conserved manner, initiated in G1 and finished in G2. Each has a pair of centrioles.
Are centrioles required for microtubule nucleation? Is the pericentriolar matrix? Wat about the gamma tubulin ring complex?
Centrioles are not required
Pericentriolar matrix - is required
Gamma tubulin ring - is required.
What percent of gamma tubulin complexes are MTOCs?
20%
The remaining 80% of gamma tubulin complexes do something else.
What is a gamma tubulin ring complex?
Located in the pericentriolar matrix blocks minus end growth binds to MT minus ends does not block plus end growth. involved in initial seeding and formation
It interacts with a beta subunit to seed microtubule formation at the centrosome. It associates with microtubule plus ends… It can cause microtubule nucleation on existing microtubules
80% of gamma-tubulin complexes at non-centrosome locations and function to produce new MT nucleation along existant MT bundles.
Abbreviated gamma-TuC
How many motors are there?
Multiple motors in each organism and each is distinct in sequence.. They can share essential functions. Proper spindle assemby requires motors that push in opposite directions. So you need overlapping/antagonistic motors.
How do you coordinate multiple motors?
Transient steady states depends on balance of forces generated by multiple complementary / antagonistic motors
Tipping balance by up or downregulating a set of motors drives specific mitotic movements.
What happens during prophase?
- Centrosomes separate
- Chromosomes condense
- Interphase microtubules break down.
- Nuclear envelope is not apparent.
- end directed c terminal kinesins (pole-pole: inward) - minus end directed kinesin pulls the poles closer together.
- end directed dynein (pole-pole: outward) - minus end directed, connecting it to the cell membrane, so cell body moves out.
- Polymerization at plus ends.
Net action is to pull poles toward the center.
Good piture of this.
Prometaphase to metaphase
- Nuclear envelope breakdown
- Polar microtubules interdigitate
- Chromosomes are captured and align on the metaphase plate. Basically during metaphase the chromosomes align.
- end directed c terminal kinesins (pole-pole: inward)
- end directed dynein (pole-pole: outward)
- end directd bipolar kinesins - Cin8 and kip1 in yeast. - push the poles away from one another. pole-pole outward. Pushes poles farther away, now things elongate.
Overexpression of CIN8P will elongate faster.
What happens if you delete one motor in yeast? What about multiple motors?
1 - cell is viale. Multiple - cell is dead.
What is chromosome capture and alignment
I think these are experiments where you use a laser to cut parts of the chromosomes and you can observe when you do this polar wind blowing the chromosome away (this is due to a kinesin causing mvmt toward the plus end.
Kinetochore
A centromere (DNA sequence) and microtubules and other proteins. 20-25 microtubules per kinetochore. Conserved.
In yeast - complex of a small centromere 120 bp + proteins, 1 microtubule per kinetochore
Metaphase
?
Anaphase
Anaphase A - chromosomes start to move toward pole but spindle size is the same. Breakdown of sister chromosome cohesion proteins… I think this means that the sister chromosomes move away from each other but the poles are the same distance apart.
Anaphase B - chromosomes move toward the pole but spindle size is elongating. Forces are generated at the kinetochore (minus-end-directed) and differential microtubule shortening at both ends. I think the poles are farther apart.
Two models for microtubule destabilization? (and movement? in anaphase?)
- Pacman model: There are proteins chewing away the microtubule plus ends.
- Poleward flux model: if you label tubulin subunits, you can see movement.
What provides the force during anaphase A to drive chromosome movement toward the spindle pole?
Disassembling microtubules, apparently. Disassembling microtubules at the plus end along with an Ska1 complex next to the kinetochore creates force which drives movement??