Mitosis Worksheet Flashcards
How does the cell know that it is ready to enter mitosis?
passes G2 checkpoint - DNA is completely replicated and there’s no DNA damage; regulated by MPF
Define interphase and M (mitotic) phase.
I: all parts of the cell cycle that aren’t mitosis; subdivided into G1, S, and G2 phases
M: cell division phase where the nucleus and cytoplasm are divided into 2 daughter cells
What are the components of MPF? What is the mechanism that regulates MPF? What are the substrates of MPF?
> Cdk1 and Cyclin B
CAK adds P to Thr 161 and Wee1 kinases adds P to Tyr 15 on Cdk1; Thr 161 P for activation, Tyr 15 P for inhibition; when G2 cleared, cdc25 phosphatase dephosphorylates Cdk1 at Tyr 15
condensins, cohesins, MAPs, motor proteins, and lamins
How is the mitotic spindle formed?
growth of microtubules out from centrosomes
How do the different types of microtubules form the spindle?
> astral - grow from centrosome toward cell periphery; + ends attack to cell cortex through - end directed motor proteins
kinetochore - attach to chromosomes at + ends through kinetochore
chromosomal - attach to ends of chromosomes
polar - from each spindle pole, overlap at + ends at center of cell
What is the role of each type of spindle microtubule in mitosis?
> astral - orient the spindle and help to separate spindle poles at anaphase
kinetochore - moves chr. from metaphase plate to spindle pole
chromosomal - positions chr. on metaphase plate
polar - separate spindle poles
What is the mechanism of chromosome alignment on the metaphase plate?
> kinetochore microtubules attach to chromosomes at kinetochores –> starts chr. movement (Aurora B involve)
(-) end motor proteins - pull toward centrosomes
(+) end motor proteins (growth of mt’s) - push away from poles
each sister chr. will have a mt attach at a kinetochore –> 1 from each pole
balance of push/pul forces aligns chr. on metaphase plate –> point equidistant from both poles
What is the structure that attaches the chromosomes to the spindle microtubules? Why is it necessary that every chr. have a bipolar attachment to the spindle?
kinetochore; to ensure proper segregation at anaphase
What is the spindle checkpoint? Describe its mechanism, including all components.
> ensures chr. attached to spindle properly before anaphase
CENP-E attaches to microtubules and BubR1, CENP-E senses tension; if improper attachment, BubR1 adds P to Mad1p–> act. Mad2p –> inhibits APC by preventing Cdc20 binding; when CENP-E sense everything is correct, BubR1 inact. –> Cdc20 binds APC
What are the two parts of anaphase and the processes that take place in each part?
A: chr. separate and move to opposite poles due to disassembly of kinetochore microtubules at their + ends; motor proteins also involved
B: polar mt’s elongate and kinesins push poles apart; astral mt’s via dyneins at cell cortex pull poles toward periphery
How is chromosome segregation regulated?
motor proteins, kinesins, dyneins, and APC ?
What is the APC, and what are its targets?
anaphase promoting complex containing an E3 ubiquitin ligase, targets securin and cyclin B for degradation by the proteasome; securin degraded first; securin inhibits separase (which degrades cohesins); loss of cyclin B inact. Cdk1
How is the nucleus reassembled during telophase?
vesicles form around chr., vesicles fuse to form nuc. membrane, nuclear pores reassemble, Lamins A and C imported from cytoplasm to complete nuclear lamina, and chr. decondense
What regulates the formation of the cleavage furrow at cytokinesis?
> phosphorylation of myosin
MPF keeps myosin light chain phosphatase in act. state, which keeps myosin in a deP state
MPF declines during anaphse, incr. in Ca2+ act. myosin light chain kinase, P added to myosin
