cell cycle Flashcards
what are the 4 main divisions of the cell cycle
g1 phase, s phase, g2 phase, cell division
what does the s stand for in the s phase
synthesis
why do cells enter the G0 phase
if there are insufficient nutrients, or the cell has become terminally differentiated (such as nerve cells as they cannot replicate)
under what situation is the G0 phase reversible
lack of nutrients, can re-enter the cell cycle after a return to the normal level
under what situation is the G0 phase irreversible
differentiation or senescence (gradual deterioration of the cells)
what is the typical length of the Mitotic stage of the cell cycle
1 hour
what is the typical length of the G1 stage of the cell cycle
5-6 hours
what is the typical length of the S stage of the cell cycle
10-12 hours
what is the typical length of the G2 stage of the cell cycle
4-6 hours
when do cells divide
when given signals
under suitable conditions
what are the 3 main check points in the cell cycle
1- G2/M
2- spindle checkpoint
3- G1
what is the G2/M checkpoint looking for
DNA damage
what is the spindle checkpoint looking for
that chromosomes are correctly attached to the mitotic spindle
what is the G1 checkpoint looking for
correct cell size, sufficient nutrients, DNA damage, growth factors
what enzyme controls the cell cycle control
cyclin dependant kinases (Cdk’s)
what do protein kinases phosphorylate
other proteins
how do Cdk’s become active
if its coupled to cyclin
which cyclins are expressed during the G1 phase
cyclin D and cyclin E
which cyclins are expressed during the S phase
Cyclin D, E, A and B
which cyclins are expressed during the G2 phase
cyclin A, B, and D
which cyclins are expressed during the Mitosis phase
Cyclin A, B, and D
the G2M is controlled by what?
MPF (maturation promoting factors)
what is the MPF made up of
Cyclin B and Cdk 1
what are the stages of MPF regulation
MPF gets dephosphorylated (looses 2 phosphate groups)
MPF then becomes active allowing cells to under go mitosis
Cyclin B then degrades leaving Cdk 1
Cdk1 is then dephosphorylated again
synthesis of cyclin B occurs and the 2 bind
and get phosphorylated by 3 phosphate groups and they’ve now become MPF again
what does the spindle checkpoint look for
- ensures chromosomes are aligned correctly ( one chromatid to each pole via kinetochores)
what is the spindle checkpoint controlled by
APC - anaphase promoting complex
what is APC activated by
MPF
what happens when APC is activated
it activates enzymes that break down protein complex at the centromere
what is the G1/S checkpoint driven by
retinoblastoma protein (pRb - is also a tumour suppressor gene ) and E2F
how can pRB become activated after an injury
when injured a signal is released from the area e.g. wounding, where blood platelets release PDGF (platelet derived growth factor)
- this causes PDFG to bind to receptors on the skin fibroblasts
- this stimulates the production of Cyclin D
- Cyclin D binds to Cdk and activates enzymes
- stimulate skin fibroblasts to divide so progression occurs from G1 to S
- causing the wound to be repaired
what is the role of Rb in the G1/S
pRb associates with E2F in G0 and early G1 blocking the transactivation domain
in what cancers is the Rb mutated
retinoblastoma
what is the stages of normal P53 function
1- DNA damage is noticed
2- cell division stops and p53 triggers enzyme to repair damage
3- P53 triggers the destruction of cells damaged beyond repair
what is the stages of abnormal P53 function
1- DNA damage is noticed
2- P53 fails to stop cell division, so cells continue to divide
3- continual division occurs, if another damage is sustained the cell may become cancerous
why are elephants less susceptable to cancer
they have more copies of p53 (40 copies)
the elephants cells kill mutated cells rather than trying to repair them
