7R: Mitosis and Meiosis Flashcards
Tubulin polymerization
- GTP bound tubulin is straight (induces polymerization)
- GDP bound tubulin is kinked (decreased stability)
- composed of alpha and beta tubulin
microtubulin binding proteins
polymerases: XMAP215
depolymerases: kinesin 8 and kinesin 13
Define:
a. astral microtubules
b. kinetochors microtubules
c. opposing microtubules
a. radiate from the centrosome and anchors the centrosome. Latches onto the cell cortex.
b. bind at the kinetochore/centromere and stabilize the + end of the microtubule, which gives us a “k-fiber” or kinetochore fibers that are stable
c. provide spindle structure and interacts with opposing overlap microtubules. (what kinesins/dyneins bind to)
centrosome
“microtubule organizing centers”
- comprised of gamma-tubulin
- has a pericentriolar space that has proteins that will help stabilize the centrosome
mother centrosome
- present in all cells in all phases of the cell cycle
- organizes the primary cilia
- duplicated during S phase to create the “daughter centrosome”
How is the centrosome duplicated?
- CDK2-cyclin E go around and phosphorylate the proteins in the pericentriolar space.
- which leads to the splitting of the mother centrosome
- then duplicated and forms 2 centrosomes
How do we deal with errors in centrosome duplication?
- p53 is activated and shuts down the cell cycle, and if it’s bad enough starts apoptosis
- defects in p53 could lead to daughter cells with the wrong amount of DNA (aneuploidy)
How do K fibers bind to the chromosome?
- K-fibers bind at the kinetochore, which binds to the centromeric DNA
- the kinetochore stabilizes the + end of the tubulin
How does the kinetochore attach to the centromere?
- the kinetochore attaches at the centromere because it is made of special histones called CENPA
- There is also a lot of cohesin at the centrosome that helps the kinetochore bind and form a stable complex
3 kinases involved in spindle formation
- Aurora Kinase A
- Aurora Kinase B
- Polo Like Kinase
- expressed only at M phase
- cancer cells over-express these in order to increase growth
SAC (Spindle Assembly Checkpoint)
SAC is ON until both kinetochores of all chromosomes are bound by k-fibers
- when you only have one of the two kinetochores bound, the MCC (mitotic checkpoint complex) forms
- the MCC inhibits the Anaphase Promoting Complex (APC) so that the cell can’t go into anaphase until metaphase is done correctly
APC (Anaphase Promoting Complex)
- a Ubiquiting Ligase Complex that allows you to switch out many different E1’s, E2’s, and E3’s to allow for large substrate specificity
- allow that cell to move from metaphase to anaphase
How does the MCC inhibit the APC?
- when a kinetochore isn’t bound, it gives off a “wait signal” which is MAD1 and MAD2
- MAD2 (in the closed conformation) will bind CDC20 and bring it to the APC
- once bound to the APC, BubR1 and Bub3 will bind the APC and kick off MAD2
How is the APC activated once all kinetochores are bound?
- once all kinetochores are bound, proteins will convert MAD2 to the open conformation and is removed from the spindle midzone
- then Cdc20 is the ubiquinated, and this disrupts it’s interaction with the MCC, and MCC is degraded
- then APC can then degrade cyclin A and B and securin to move to anaphase
Define:
a. kinesins
b. dyneins
c. myosin proteins
a. motor protein that moves on microtubules towards the periphery
b. motor protein that moves on microtubules towards the center of the cell
c. motor proteins that move along actin
- all require ATP hydrolysis
