cell cycle Flashcards
what do centrosomes consist of
pairs of centrioles, made of triplets of microtubules
what do microtubules do?
radiate out from centrosome and attach to chromosome
what happens as microtubules grow and shrink?
chromosomes are pulled to the poles
what are many microtubules called?
k fibres (kinetochore fibres)
alpha-tubulin
dimer that makes up microtubules
beta-tubulin
dimer that makes up microtubules
kinetochore
made of many proteins, forms on the mitotic chromosomes adjacent to the centromeres allowing microtubules to bind
prophase
chromosomes condense and envelope breaks down, centrosomes start to migrate and make microtubules
prometaphase
chromosomes fully condensed but not aligned, NE fully digested, microtubule capture, centrioles position
metaphase
chromosomes aligned at plate, amphitelic microtubule attachment, CHECKPOINT
what does amphitelic microtubule attachment mean?
microtubules have captured chromosomes equally on either side
anaphase
sister chromatids detach and move towards poles
telophase/cytokinesis
NE reforms, chromosomes decondense, cleavage furrow
what is cleavage furrow?
the pinching in the centre of the cell when it splits
lagging chromosome
when one chromosome goes to wrong cell because of incorrect microtubule attachment
what is the correct type of microtubule attachment?
amphitelic attachment
syntelic attachment
microtubules from one side attaches to both
monotelic attachment
microtubules only attach on one of the sides
merotelic attachment
bipolar attachment with another from one side
what do the wrong attachments of microtubules result in
unequal forces and therefore a lagging chromosome
what happens when attachment of microtubules goes wrong
polyploidy
polyploidy
abnormal number of chromosomes
describe G1
highly metabolically active, cell growth, duplication of organelles (8-10 hrs)
describe S phase
DNA replication, centrosome duplication (6-8hrs)
Describe G2
more cell growth, accumulation of key enzymes needed to trigger entry into mitosis, cytoskeleton preps for remodelling required in cell division
how does a CDK work
it bind to a cyclin and then it can phosphorylate
what do CDKs and cylins do to the cell cycle?
pushes it forward
how does a CDK-cyclin complex activate a target protein?
phosphorylates it
what happens after CDK-cyclin complex activates the target protein?
it disperses and can no longer activate proteins
what is a PTM
post-translational modification
what phase is cyclin D in
G1
what phase is cyclin E in
G1/S
what phase is cyclin A in
S/G2
what phase is cyclin B in
M
what phase are CDK 6 and 4 in
G1
what phase is CDK 2 in
S
what phase is CDK 1 in
G2/M
what happens at G1/S checkpoint
DNA damage checkpoint, if there is DNA damage the cell cycle stops
what happens at G2/M checkpoint
DNA damage checkpoint
what happens at M checkpoint
spindle assembly checkpoint
what do DNA damage checkpoints do
sense for ‘favourable conditions’ cell size, growth factors and DNA damage
what happens if DNA damage is detected
increase in P53 and P21
what does P21 do
inhibits CDKs which leads to cell cycle arrest or apoptosis
what happens at a spindle assembly checkpoint
BubR1 sits on kinetochore until microtubules are stably attached, it leaves and then activates the Anaphase Promoting Complex (APC), APC releases separase which cuts the sister chromatids ONLY if there is proper microtubule attachment
example of mutations to key regulators - BubR1 gene
aberrant checkpoint signalling promotes cells with abnormal number of chromosomes leading to cancer
example of mutations to key regulators - retinoblastoma (Rb)
CDK phosphorylates Rb, E2F transcription factor released by Rb, if mutated then too much E2F released, too many cyclins are produced so cell cycle is no longer controlled
what shape are cells in interphase and what shape are mitotic cells
interphase - flat, mitotic - round
what do centrosomes do
radiate microtubules
what are multipolar spindles
microtubules attach in many different directions due to the cell having 3 centrosomes so 3 cells form
what happens in G0
many cells differentiate and exit the cell cycle
Cell cycle control - example of targets (Rb and E2F)
after mitosis growth factors are expressed as well as cyclin D and CDK 4&6, Rb binds to E2F (TF) and holds it if inactive. CDK cyclin complexes phospho’s Rb, E2F goes to nucleus for transcription - Cyclin E is produced
