Mitosis from Rich Notes Flashcards
(31 cards)
What is the cell division phase where the nucleus and cytoplasm are divided into two daughter cells?
Mitosis
What is the last checkpoint that the cell must pass before it can go into mitosis? What does it confirm?
G2; DNA is completely replicated and that there’s no DNA damage
Entry into mitosis is regulated by what factor?
MPF
MPF is a complex of what?
Cyclin B and Cdk1
How is MPF activated?
During interphase, cyclin B made and complexes w/ Cdk1, CAK primes Cdk1 w/ P on Thr 161, activates Cdk1, at same time - Wee1 kinase adds P to Tyr 15 on Cdk1, this inhibits Cdk1 until cell ready for division; once G2 cleared, cdc25 phosphatase takes off P of Cdk1, MPF now active and adds P to substrates in mitosis
What are the key targets for MPF phosphorylation?
Hint: 3 processes and 5 types of proteins
chromosome condensation - condensins and cohesins
spindle formation - microtubule associated and motor proteins
nuclear envelope breakdown - lamins
During prophase, what do the centrosomes and microtubules do?
Centrosomes move to opposite sides of nucleus.
Microtubules grows out from centrosomes to form spindles.
What two protein complexes are responsible for maintaining chromosome stability during mitosis?
cohesins and condensins
During S phase, the cohesin complex binds to what?
newly made sister chromatids
What phosphorylates cohesins during prophase along the arms of the chromosomes except at the centromere? What does this allow the chromosome arms to do?
MPF; separate and be compacted by condensins
What triggers condensin import into the cell? What energy source does condensin use to compact the chromatin? What does the compaction prevent?
phosphorylation of accessory proteins by MPF; ATP hydrolysis; chromosomes from being tangled and broken, RNA synthesis
Phosphorylation of the nuclear lamins by MPF causes the nuclear lamina to disassemble and the membrane to fragment into vesicles. What lamin remains with the vesicles? What lamins disperse into the cytoplasm along with nuclear pore complexes?
B; A and C
Generally speaking, what happens during prometaphase?
Spindle formation continues and chromosomes attach to the spindle through the kinetochore.
MPF phosphorylates what proteins during prometaphase to regulate the balance between assembly and disassembly of the microtubules?
MAPs and motor proteins
What are the four types of microtubules in the mitotic spindle? What do they each do?
> astral - orient spindle and separate it during anaphase
kinetochore - move chr. from metaphase plate to spindle pole through attachment at kinetochore
chromosomal - help position chr. at metaphase plate
polar - help separate the two poles
What drug stabilizes microtubules, preventing disassembly? (It interferes w/ the ability of the microtubules to align the chr. on the metaphase plate and to move the chr. to the spindle poles.)
paclitaxil (taxol); used as chemotherapy agent to prevent proliferation of cancer cells
What is a specific region of DNA that contains repetitive sequences but also binds to CENP that in turn binds kinetochore proteins?
centromere
What binds to either side of the centromere and forms attachment site for the mitotic spindle?
kinetochore; some of its proteins are involved in the spindle checkpoint
Chromosomes are aligned on the metaphase plate. To ensure that each daughter cell gets one copy of each chromosome, the cell has to pass the spindle checkpoint. What happens during the spindle checkpoint?
CENP-E attaches to both mt’s and BubR1 on the kinetochore, CENP-E senses the tension; BubR1 regulates Mad1p –> act. Mad2p –> inhibits APC through prevention of Cdc20 binding –> prevents mitosis; bipolar orientation achieved, CENP-E inact. BubR1–> Cdc20 binds APC, mitosis proceeds to anaphase
What happens during anaphase A? What happens during anaphase B?
A: chromosomes separate through disassembly of kinetochore microtubules and move to opposite poles; motor proteins also involved
B: spindle poles move apart: polar microtubules elongate and kinesins push the poles apart, astral mt’s via dyneins at the cell cortex pull the poles toward the periphery
What enzyme does the anaphase promoting complex contain? When the APC is activated, what two proteins does it target for degradation by the proteosome?
E3 ubiquitin ligase
securin and cyclin B
When securin is destroyed, what happens?
separase is activated and degrades cohesins; chromosomes are free to move to opposite poles in anaphase
When Cyclin B is destroyed from targeting by APC, what happens?
Cdk1 is inactivated and exit from mitosis is triggered
Does it matter if securin or cyclin B is degraded first?
yes; securin has to be degraded first; cyclin B is then destroyed, which reverses all of the phosphorylation from prophase and prepares cell to divide
