cell cycle Flashcards
cell cycle: recall the various cell cycle phases, and demonstrate the ability to label and annotate a diagram of the cycle. Explain the functions and properties of each phase, and recall how the cell is directed to divide, differentiate, or undergo apoptosis
what 5 things affect rate of cell division
embryonic vs adult, complexity of system, necessity for renewal, state of differentiation (antagonistic with division), tumour (lose ability to control, and don’t follow rules)
define cell cycle
orderly sequence of events in which a cell duplicates its contents, segregates them and divides in two
2 overall phases of regulated progression through cell cycle
M-phase (mitosis), interphase
what happens during mitosis
nuclear division, cell division (cytokinesis)
what happens during interpahse
DNA and organelle duplication, increase in protein synthesis
what is the most vulnerable period of the cell cycle
mitosis
why is mitosis the most vulnerable period of the cell cycle
cells are more easily killed (irradiation, heat shock, chemicals), DNA damage can’t be repaired, gene transcription is silenced
4 phases within interphase
G0, G1, S, G2
what happens in G0
cell cycle machinery dismantled; cell does its function (e.g. secretion)
what happens in G1 phase (Gap)
decision point after mitosis/G0
what happens in S phase
synthesis of DNA and protein
what happens in G2 phase (Gap)
decision point before mitosis
what 3 things are increased in S phase
initiation of translation, elongation and capacity for protein synthesis
how is mitochondrial replication in S phase different to replication of other organelles
must coordinate with replication of mitochondrial DNA
what does the centrosome consist of
2 centrioles at 90 degrees to each other, maintained in position by interconnecting fibres
what are centrioles
barrels of 9 triplet microtubules
2 functions of centrosome
microtubule organising centre (MTOC) and mitotic spindle
life cycle of centrosomes during mitosis
during G1, microtubules grow from centrosome (pair of centrioles), before one centriole detaches -> during S, they duplicate -> in M, when cell divides, each cell has a fully functioning centrosome, consisting of 2 centrioles and microtubules
what do microtubules polymerise from in centrosomes
nucleating sites (y-tubulin ring complexes), which encompass a pair of centrioles
6 phases of mitosis
prophase -> prometaphase -> metaphase -> anaphase -> telophase -> cytokinesis
what happens in prophase
condensation of chromatin
stages of chromatin condensation in prophase
chromatin -> condensed scaffold-associated form -> extended scaffold-associated form -> 30nm chromatin fiber of packed nucleosomes -> “beads on a string” form of chromatin around histone proteins -> short region of DNA double-helix
in prophase, what does each condensed chromosome consist of
2 sister chromatids, which are joined at the centromere which is associated with a kinetochore
3 things that happen between prophase and late prophase-prometaphase
replicated chromosomes condense -> duplicated centrosomes migrate to opposite sides of nucleus and organise assembly of spindle microtubules -> mitotic spindle forms outside nucleus between 2 centrosomes
3 stages of spindle formation
radial microtubule arrays (ASTERS) form around each centrosome MTOC -> radial arrays meet -> polar microtubules form (dynamic in this position at centre of cell)
what happens in metaphase
chromosomes align at equator of spindle
2 stages of prometaphase
early, late
3 things that happen in early prometaphase
breakdown of nuclear membrane -> spindle formation largely complete -> attachment of chromosomes to spindle via kinetochores (at centromere)
3 things that happen in late prometaphase
microtubule from opposite pole captured by sister kinetochore -> chromosomes attached to each pole progress to middle -> chromosome slides rapidly towards centre along microtubules (CENP-E senses kinetochore tension to ensure this is correct)
what happens in anaphase
paired chromatids separate to form daughter chromosomes
within the multiprotein complex, what protein holds sister chromatids together, and hence must be broken down
cohesin
2 stages of anaphase
A, B
what 3 things happen in anaphase A
breakdown of cohesin -> microtubules get shorter -> daughter chromosomes pulled toward opposite spindle poles
what 2 things happen in anaphase B
daughter chromosomes migrate towards poles -> spindle poles (centrosomes) migrate apart
what 3 things happen in telophase
daughter chromosomes arrive at spindle -> nuclear envelope reassembles at each pole -> assembly of contratile ring (of actin and myosin filaments, creating cleavage furrow)
what 6 things happen in cytokinesis
new membrane inserted -> acto-myosin ring contracts -> midbody begins to form -> interphase microtubule array reassembles -> chromatin decondenses and nuclear substructures reform -> midbody splits
what 2 things happen if something goes wrong during cell cycle (cell not big enough or DNA damage)
cell cycle arrest, programmed cell death (apoptosis)
where does cell cycle arrest occur
at checkpoints (G1 and spindle check point); can be temporary (i.e. following DNA repair)
3 occasions when apoptosis occurs and cell cycle progression aborted and cell destroyed
if DNA damage is too great and can’t be repaired, chromosomal abnormalities, or with toxic agents
