2.6: The Cell Cycle Flashcards
define the cell cycle
sequence of events where contents of a cell are duplicated and divided into 2
do all cells divide at the same time
no bro why would they
define interphase and what are the sub-phases in interphase
interphase is the period between cell divisions: metabolic activity, cell growth, repair
composed of g1 phase, s phase (synthesis), g2 phase
define m phase and what is included in it
m phase is when the nucleus and the cytoplasm divide
includes mitosis (nuclear division) and cytokinesis (cytoplasmic division)
provide example of cells that normally divide on an ongoing basis
hematopoietic and epithelial stem cells
provide an example of a cell that only divides when given an appropriate stimulus
when damaged, liver cells start to divide and replace damaged tissues
provide an example of a mature cell that does not divide
terminally differentiated cells - nerve cells, muscle cells, red blood cells - as they became differentiated, they lose the ability to divide
do cells divide in g0 and are they functional
no cell division but still metabolically active as to carry out cell functions - g0 means it is resting and there is no proliferation
list the major checkpoints of the cell cycle control system, when they occur, and what does it check for
- start transition: g1 –> S: is the environment favorable (eg sufficient nutrients, specific signal molecules)
- g2/m transition: g2 –> m: is all dna replicated, is all dna damage repaired
- spindle assembly checkpoint: metaphase to anaphase transition: checks if all chromosomes attached properly attached to the mitotic spindle to pull duplicated chromosomes apart
what is the point of the cell-cycle control system
delays later events until the earlier events are complete
problems in the checkpoints of the cell cycle control system can lead to what
chromosome segregation defects
what is the point of the mitotic spindles
Structure that allows to line up all the chromosomes so that they are ready to be separated
cell cycle progression is controlled by _____________
cell cycle progression is controlled by molecular switches
entry into next phase of the cell cycle is triggered by __________
cyclin dependent protein kinases (Cdks)
are cyclin-Cdk complexes activated or inactivated for entry
activated
what Cdks is used for entry into the M phase
M-Cdk (Cdk activated by M cyclin) which phosphorylates other regulatory proteins
Cdks binds to what in order to by activated
cyclins (its in the name)
for each major checkpoint in the cell control system, what might inhibit the Cdk if the cell is not ready:
- start transition: g1 –> S: Cdk inhibitors
- g2/m transition: g2 –> m: inhibition of activating phosphatase (Cdc25)
- spindle assembly checkpoint: metaphase to anaphase transition: ihibition of APC/C activation delays exit from mitosis
why do chromosomes condense during prophase
to avoid damage to the dna
during what phase of interphase are the following events happening in:
- centrosome duplication initiated and completed by g2
- chromosomes replicated (decondensed)
- replicated chromosomes dispersed, tangled so they need to reorganize and condense for mitosis
G1 phase - centrosome duplication initiated and completed by g2
S phase - chromosomes replicated (decondensed)
G2 - replicated chromosomes dispersed, tangled so they need to reorganize and condense for mitosis
what 2 main events happen during prophase
- replicated chromosomes condense (chromatids compacted and sister chromatid resolution (separable units - removes cohesins))
- mitotic spindle assembly starts and requires duplicated centrosomes
___________ (a protein) is deposited to hold 2 sister chromatids together during s phase
cohesins deposited to hold 2 sister chromatids together (The 2 sister chromatids (2 double stranded molecules that are identical)are held together by the cohesin rings
)
differ between cohesins and condensins
Cohesin - hold sister chromatids together
Condensin - make arms together (makes the loops of DNA by like pinching it)
during prophase, _________ removed from chromosome arms but not from centromeres
cohesins
during prophase, _______ condense DNA in each sister chromatid
condensins
during prophase, sister chromatids are resolved but remain associated at the centromere by __________
cohesins
dynamic __________ are required for mitosis
dynamic microtubules are required for mitosis
in non dividing cells, microtubules are arranged in a radial pattern, which ends are radiating out and which end is stabilized at mtoc (centrosome)
+ out
- stabilized at mtoc
fill in the blank: microtubules are
made up of __________ ________ which bind to each other in linear array to form a ____________. __ (#) protofilaments make a microtubule. It’s really about the __________ of the heterodimers (____ tubulin at + end and _____ tubulin at - end = polarity)
microtubules are
made up of tubulin heterodimers which bind to each other in linear array to form a protofilament. 13 protofilaments make a microtubule. It’s really about the orientation of the heterodimers (beta tubulin at + end and alpha tubulin at - end = polarity)
in order for mitotic spindle assembly to begin, list the two conditions
- requires dynamic disassembly of microtubules
- requires duplicated centrosomes
there is a pair of __________ in the centrosome, and describe their organization and composition
pair of centrioles, organized at right angles to each other and composed of 9 fibrils of 3 microtubules each (ABC triplet)
the centrosome matrix surrounds the pair of centrioles, what does it contain in order to nucleate sites to assemble new microtubules
it contains y tubulin ring complexes (y-TuRCs)
how many times are centrosomes duplicated during interphase
once
in between which subphases does centrosome duplication occur
intitated in g1 phase and completed by g2
what do duplicated centrosomes form
they form poles of mitotic spindle
each centriole in a pair serves as a site for what
a site for assembly of a new centriole
during which phase does mitotic assembly begin in
prophase
when duplicated centrosome separate, what happens to the microtubules
radial array of microtubules extend out from each to position centrosomes which will become the two spindle poles
what comes after the creation of spindle poles and why
nuclear envelope breakdown so that the mitotic spindle can access the chromosomes
nuclear envelope breakdown occurs at the boundary between ….
between prophase and prometaphase
what is the nuclear lamina
meshwork of interconnected nuclear lamin proteins (nuclear intermediate filaments) which forms a 2d lattice on the inner nuclear membrane
(kinases) phosphorylation of lamins and nuclear pore proteins triggers what
triggers disassembly of nuclear envelope into small membrane vesicles
an interphase nucleus is composed of 4 main parts, list them
- nuclear pore
- lamins
- dna
- nuclear envelope
what has happened in prometaphase (regarding nuclear envelope, mitotic spindles, kinetochore microtubules, chromosome movement)
- nuclear envelope now disassembled
- mitotic spindle assembly can be completed
- kinetochore microtubules in the mitotic spindle - attach to duplicated chromosomes
- chromosome movement begins
2 factors that mitotic spindle assembly and function requires:
- microtubule dynamics
- microtubule motor protein activity (kinesins, cytoplasmic dynein)
(recc to look at diagram) regarding the completion of the mitotic spindle assembly, what is the point of astral microtubles
help position the mitotic spindles - cytoplasmic dynein
(recc to look at diagram) regarding the completion of the mitotic spindle assembly, what is the point of non-kinetochore microtubules
cross linked microtubules throughout the mitotic spindle (kinesin-5 (moves toward plus ends), other microtubule associated proteins)
(recc to look at diagram) regarding the completion of the mitotic spindle assembly, what is the point of kinetochore microtubules
attach duplicated chromosomes to the spindle poles
(recc to look at diagram) regarding the completion of the mitotic spindle assembly, which direction do dynein and kinesin-5 (motor protein movement) go along the microtubule
dynein towards minus end and kinesin-5 toward +
where are kinetochores located
centromeres of chromosomes
__ (#) kinetochore(s) for each sister chromatid in the duplicated chromosome
1
do microtubules from both spindle poles must attach to kinetochores of sister chromatids
yes, both
when microtubules from both spindle poles must attach to kinetochores of sister chromatids, what happens
generates equal tension on both sides to line up chromosomes at equator of spindles = more stable - Microtubule dynamic instability still happening, the mitotic spindle not only catches the duplicated chromosomes but it also lines it all up at the equator of the mitotic spindle
to which sides of the microtubule do connecting protein complexes attach close to and what which end is exposed
connecting protein complexes bind to sides of microtubule near + end
microtubule exposed + end
what happens when the connecting protein complexes binds to microtubules and the microtubule + end is exposed
it allows for growing or shrinking for chromosome movement
to maintain the metaphase spindles - what must happen
tubulin flux
- addition of tubulin subunits at + end
- removal of tubulin subunits at - end
- length of kinetochore microtubules does not change
during tubulin flux of microtubules, does the length of kinetochore microtubules change
no
what happens during metaphase
all chromosomes are aligned on the metaphase plate (equator of the spindle) and microtubule dynamics continue to maintain the metaphase spindle (tubulin flux)
where is the metaphase plate
equator of the spindle
how was tubulin flux observed
a small amount of fluorescent tubulin added to observe microtubule flux, time lapse microscopy used to follow fluorescent tubulin movement
during tubulin flux, removal by depolymerases is at which end of the microtubule
-
what is the checkpoint in between the metaphase and anaphase transition
spindle assembly checkpoint
what enzyme is activated during anaphase
separase
how are separation of sister chromatids conducted during anaphase
separase is activated which cleaves the cohesion complex thereby releasing sister chromatids (once separated, they are referred to as chromosomes)
during anaphase (a and b):
kinetochore microtubules are ____________ (____ of tubulin at both ends)
_____________ are puled apart towards opposite poles
spindle poles move _________ (kinesin, cytoplasmic dynein)
kinetochore microtubules are shortened (loss of tubulin at both ends)
sister chromatids are pulled apart towards opposite poles
spindle poles move outward (kinesin, cytoplasmic dynein)
how are sister chromatids separated with kinesin and cytoplasmic dynein
sliding force by kinesin (from opposite poles pushes the poles apart) and pulling force by cytoplasmic dynein (drags the two poles apart)
during which phase are chromosomes now separated into two groups (one at each spindle pole)
telophase
during telophase:
mitotic spindle _________
nuclear envelope _________
chromosomes _________ (into interphase state)
_________ starts to assemble (for cytokinesis)
mitotic spindle disassembles
nuclear envelope reassembles (need 2 of it now)
chromosomes decondense (into interphase state)
contractile ring starts to assemble (for cytokinesis)
describe the reassembly of the nuclear envelope
dephosphorylation of nuclear pore proteins and lamins by phosphatases which cause the vesicles to fuse together such that the nuclear envelope reassembles with nucelar lamina (lamins) and nuclear pores so the localization of proteins can be restores. this dephosphorylation happens in between prometaphase and telophase.
cytokinesis requires:
dynamic actin and myosin filaments
how is the cytoplasm divided into two and where is it divided during cytokinesis in animal cells
divided by a contractile ring of actin and myosin filaments at the cleavage furrow (midway between the spindle poles)
where is the cleavage furrow (in between what)
midway between the spindle poles
_______________ reforms in each daughter cell during cytokinesis in animal cells
interphase microtubules
the contractile ring is formed where at the end of mitosis
underneath the cell membrane
what force brings in cell membrane in as contractile ring becomes smaller and divides cell into two daughter cells (cytokinesis in animal cells)
contractile force
compare mitotic spindle vs contractile ring
dynamic cytoskeletal structures play very important roles in mitosis and cytokinesis in animal cells
both structures disassemble rapidly after task is completed
mitotic spindles are made up of microtubules
contractile rings are made of actin and myosin filaments
what is diff between mitosis of plant and animal cells
no centrosome (theres another mech to form mitotic spindles in plant cells)
describe cytokinesis in plant cells: telophase, cytokinesis, g1
telophase:
- chromosomes separated into 2 sets
-phragmoplasts start to form: specific structure to form cell plate, has microtubules, actin filaments, vesicles, from golgi (needed to form cell wall)
cytokinesis:
- nuclear envelope reassembled, chromosomes decondensed
- cell plate forms: transient membrane compartment (vesicles from golgi fuse tgt) to divide cell into 2
g1:
- cell plate matured into pm and cell wall between two daughter cells
during what phase does a phragmoplast form
telophase
what does a cell plate mature into
pm and cell wall
what stage does the cell plate form
cytokinesis
compare cell division in mitosis and meiosis:
- chromosome duplication rounds, cell division rounds, produces what, homologous chromosome pairing, chromatid segregation
- both have one round of dna replication (chromosome duplication)
- meiosis has 2 rounds of cell division, mitosis has 1
- meiosis produces 4 haploid cells, mitosis 2 diploid cells
- meiosis I: homologous chromosomes are paired at metaphase plate vs mitosis homo chromo not paired
- meiosis II and mitosis both have sister chromatid segregation
differentiate between meiosis cell div round 1 and round 2
1: homo chromo segregted into 2 daughter cells (sister chromatids remain attached)
2: sister chromatids segregated, produces 4 hap cells
