Lecture 19 - Mitosis & Cytokinesis Flashcards
def: phase where duplication of all DNA in a cells chromosomes occur
S-Phase
def: phase where copies of chromosomes are segregated into the two daughter cells
M-phase
the Gap phases (G1/G2) allow time for cells to:
- double their mass of proteins and organelles
- monitor the fidelity of other processes
T or F: cells spend very little time in M-phase
true
where is most of the time spent in the cell cycle?
interphase (G1, S, and G2)
def: when the cells actually divide, the nucleus first, followed by the cytoplasm
M phase
why is chromosome condensation critical?
interphase chromatin fibres are too long and intertwined, would be impossible to untangle and distribute during cell division
how does the entire microtubule cytoskeleton disassemble as the cells progress from G2 into M phase?
- inactivation of stabilizing MAPs (Tau, MAP2, EB1)
- activation of destabilizing MAPS (Stathmin, Catastrophins, Katanins)
when does centriole duplication occur?
S phase
when do the centrioles separate?
during prophase to act as nucleation sites to form the mitotic spindle
dissolution of the nuclear envelope marks the onset of ___________________
prometaphase
the dissolution of the nuclear envelope allows what to occur?
allows the spindle microtubules to make contacts with the chromosomes
phosphorylation of ______________ proteins induces chromatin condensation and inhibits interactions between chromatin and the nuclear envelope
chromatin
phosphorylation of specific ________________ causes nuclear pore complexes to dissociate
nucleoporins
phosphorylation of _____________________ inhibits their interaction with lamina and with chromatin
inner nuclear membrane proteins
phosphorylation of human ________ _ causes depolymerization of the intermediate filament in the Nuclear Lamina
Lamin A
the mitotic spindle is completed when…..
the (+) end of MT’s from each spindle pole bind the sister chromatid at the kinetochores
def: process the begins as chromosomes move to the center
congression
microtubules attach to chromosomes in the ___________ region, at structures called _______________
centromeric, kinetochores
DNA in centromeres consists of simple, tandemly repeated _____ ________________, with considerable variation among species
CEN sequences
what is a common feature among species within the centromere?
presence of a histone H3-related protein called CENP-A (humans_
def: recruits additional proteins to the centromere to form the kinetochore to which MT’s attach
CENP-A
def: bi-directional forces exerted by kinetochore bound microtubules from each bole gradually move chromosomes toward the centre of the cell
congression
def: responsible for chromosome movements and separation of chromatids during mitosis
mitotic spindle
where are the centrosome and kinetochore located on a microtubule
- the centrosome contains the (-) end
- the kinetochore attaches to the (+) end
kinetochores are the site of :
- microtubule/chromosome attachment
- motor proteins, necessary for chromosome mobility
- signalling for important mitotic checkpoints
when is a cell considered to be in metaphase?
when the fully condensed chromosomes are aligned at the metaphase plate
T or F: the mitotic spindle is a stable structure
False, it is highly dynamic, it treadmills
the kinetochore should not be viewed as a cap protein, there is a ______ ______ of tubulin at the ____________ and a ________ at the kinetochore
net loss at centriole, net gain at the kinetochore
def: project toward the cell cortex, help position the spindle apparatus in the cell
astral microtubule
def: connect to chromosomes to the spindle poles, alight the chromosomes on the metaphase phase and pull them to the poles during anaphase
kinetochore microtubules
def: extend past the chromosomes and interact with polar microtubules from the other spindle pole, maintain integrity of the mitotic spindle and push the spindle poles apart during anaphase
polar microtubules
what is the shortest phase of mitosis
anaphase
def: abruptly separates connections between the two sister chromatids of each chromosome, allowing for movement toward the opposite poles
Separase
def: portion of anaphase where chromosomes slowly pulled centromere first toward spindle poles as kinetochore microtubules get shorter
anaphase A
def: portion of anaphase where the spindle poles themselves move away from each other as polar microtubules lengthen
anaphase B
def: bind to the ends and promotes depolymerization of MT’s at both the kinetochores an centrosome
specialized kinesisn
def: bind to overlapping polar microtubules, cause them to move apart
bi-polar kinesin 5
def: when associated with astral microtubules, moves towards the (-) ends of microtubules, pulling the spindle poles toward the cell membrane
cytoplasmic dynein
where does the force required to move chromosomes toward the mitotic poles come from?
depolymerization of the kinetochore MT
the depolymerizing kinesis removes tubulin from the :
(+) end = pulling the chromosome towards the pole as the MT disassemble
(-) end = enhancing poleward microtubule flux
def: connect MT’s to kinetochores, move along MT maintaining contact as depolymerization occurs
6-9 Ndc80 complexes
what 4 things happen during telophase?
- daughter chromosomes arrive at the poles of the spindle
- mitotic spindle disassembles
- chromosomes uncoil into interphase chromatin
- nucleoli reappear and nuclear envelopes reform
signals emanating from the central part of the spindle, the spindle mid zone, are important for establishing where __________ will occur
furrowing
cleavage depends on a belt-like bundle of _________ ____________ that form just below the plasma membrane in early anaphase
actin microfilaments
what is contraction of the contractile ring generated by?
interactions between actin and bipolar myosin II motor proteins
what regulates the assembly and activation of the contractile ring?
members of Rho family
def: final separation of daughter cells
abscission
how are large, multi-nucleated cells produced?
when a cell undergoes incomplete cell division, mitosis but no cytokinesis
control of the cell cycle must:
- ensure events of each phase are carried out in the correct order and at the appropriate time
- ensure that each phase is completed before the next one begins
- respond to external conditions
what are the 3 major checkpoints in eukaryotic cells?
- start (or restriction point) - cell commits to cell-cycle entry
- G2/M checkpoint
- metaphase to anaphase checkpoint - chromatid separation is triggered leading to completion of mitosis and cytokinesis
