9-cell cycle Flashcards
what happens in M phase? are chromosomes visible?
Mitosis/meiosis and cytokinesis. (chromosomes are splitting and visible under microscope)
what happens in S phase?
Dna synthesis
how much more growth is there in G2 in comparison to G1?
double amount of dna
what type of hydrogen was used in experiments on s phase?
radioactive H3 thymidine Tritium hydrogen
What is needed for DNA synthesis that is not ATP and allowed the S experiments to take place?
H3 radioactive hydrogen could be incorporated in TTP which would be taken up in DNA synthesis.
How did they confirm cells where in S phase half of the cell cycle time?
Autoradiograph showed half of the cells took up labelled TTP and so we can assume the cycle is in s phase half its time
how were G1 and G2 investigated?
flow cytometry
How does flow cytometry work to investigate G1 and G2?
a single cell with dye added and this binds to DNA and then measure DNA concentration G1-1/2 fluorescence of G2 G2- double flourescence of G1 this enabled estimation of time spent in G1 and G2
what did injection studies in oocytes show?
cell cycle affected by external factors such as hormones
What has progesterone got to do with frog oocytes?
progesterone was injected into frog oocytes and induced M phase then this M phase cytosol was injected to G2 phase cytosol which was then induced to go into M phase.
What is the secondary thing the frog oocyte experiment showed?
M phase cytosol injected into G2 phase induced G2 phase to go into M phase (something in M forces G2 to go to M)
what were the Hela cells used for?
Fusion experiments, the fused different cells in different phases of the cell cycle to see the effects.
what happens when s phase and G1 cells fuse?
All go into s phase. S phase contains factors that can diffuse to other nucleus and lead G1 cell to replicate DNA and enter s phase (this is visible due to use of thymidine which becomes incorporated)
What combination of cells leads to no change to either?
S phase and G2 phase. G2 is refractory and cannot be induced by s factors.
what is interphase made up of?
G1,S,G2
what happens when interphase cells (G1,S,G2) are fused with cells in M phase?
all cells enter M phase. mitotic cells forced all others to go into mitosis. This was assumed because all chromosomes then condensed.
what happens when G1 and G2 cells are fused together?
G2 loses s phase factors
what did budding yeast temperature sensitive mutants show?
They arrested(stalled) at G1 when exposed to high temperatures which revealed a first checkpoint: is my DNA damaged? (possible G0 arrest phase)
what yeast was used in the budding experiments?
saccharomyces cerevisiae Cdc28
what type of factors are the 3 main checkpoints regulated by? (2)
external and internal
what are the 3 checkpoints?
1)restriction point/start (G1) 2)G2/M 3)M
how is progress of the cell cycle affected by cyclins?
progress of cell cycle is dependent on most abundant cyclin at the time
what do cyclins do?
tell cyclin dependent kinase what to do: genes to activate,switch off,proteins to make etc)
what does CDK stand for?
cyclin dependent kinase
why do the mutant yeasts arrest?
faulty dependent kinase
at what stages do s-type cyclins increase in concentration?
G1/s/G2
at what stages of the cell cycle do s-type cyclin levels drop?
G2/M2
where does the sudden change from high conc to low conc occur,what cell phase?
G2
who discovered cyclins and whilst studying what?
They were discovered by R. Timothy Hunt in 1982 while studying the cell cycle of sea urchin
what are cyclins?
a family of proteins that control the progression of cells through the cell cycle by activating cyclin-dependent kinase (Cdk) enzymes
what do cyclins form once bound to dependent kinases?
maturation-promoting factor (MPFs)
what do MPFs activate and how?
MPFs activate other proteins through phosphorylation
What are the 4 main cyclin classes?
G1/S cyclins, S cyclins, G2 cyclins, M cyclins.
what cyclin type is involved in the checkpoint that promotes passage through the start?
G1/S cyclin
How many CDKs are there in yeast?
1 (but there are several in humans)
in which phase is the restriction point/start point?
in G1
what is the restriction point/start point deciding?
should cell divide?should division be delayed/should cell enter resting stage?
what does checkpoint of G2 about to go to M (G2 checkpoint) try do decide?
it is assessing success of DNA replication and whether to trigger start of M phase
what does checkpoint M decide?
assesses accuracy of mitosis (during metaphase) and triggers mitosis exit and beginning of G1
what cyclins are involved in start G1 checkpoint and by what mechanism are they acting?
CDK+G1 cyclin & CDK+G1/S cyclin promote passage through start by phosphorylating
give an example of something phosphorylated in start checkpoint and what is freed?
Retinoblastoma protein, which frees EF2 (a TF therefore next cell phase begins)
what can misregulation of CDKs and cyclins lead to?
uncontrolled growth (i.e. cancer)
How does a separate complex (not associated to a particular checkpoint) but found in s phase initiate dna synthesis?
CDK+S cyclin initiates DNA synthesis by phosphorylating
what can cdk and s cyclin complex phosphorylate to initiate dna synthesis? what does this stabilise?
Histone mRNA stem-loop binding protein, this stabilises histone mRNA
what is phosphorylated in G2/M checkpoint? (3)
Nuclear lamins => break down nucleus
Myosin => prevents cytokinesis
Condensin => condenses chromosomes
what complex is associated with checkpoint in G1(start)?
CDK+G1 cyclin & CDK+G1/S cyclin
what destruction is associated with checkpoint (M) ?
destruction of M cyclin by APC
what does apc do?
marks target cell cycle proteins for degradation
true or false: CDK are active without cyclins
false they are inactivated without
what is CAK?
CDK activating kinase
what is Wee1?
CDK inactivating kinase
how you activate cdk?
1) cyclin association
2) CAK is required
what state is a CDK with cyclin but not CAK?
partly active
what can reactivate a deactivated CDK/cyclin complex?
Cdc25 CDK activating phosphatase
what does cdc25 CDK do?
reactivate an inactive cdk/cyclin complex
what is does cyclin ubiquination do?
inactivates an active CDK/cyclin complex
what is APC/c and what is it involved in?
anaphase promoting complex/cyclosome and it is involved in degradation of the cyclin and phosphate
what does CAK add?
it is a kinase itself so adds a phosphate group
why is the balance of synthesis/degradation important in terms of cyclins?
this balance is how they are regulated
what is MAPK/K/K–> G1 cyclin expression?
a growth factor cascade
what is needed to padd through a restriction point (start)?
sufficient activity
what are p21 and p53?
CDK inhibitor proteins (CKIs)
what are the two CDK inhibitor proteins?
p21 and p53
what can DNA damage do in terms of p53?
can lead to phosphorylation and activation of p53 and thus expression of p21 (these are both CDK inhibitor proteins)
if there is a mutation and dna is damaged p53 detects it,accumulates and the p21 is expressed which inhibits CDK, but what does this bind to and what does it do to this?
binds to s-cyclin and inactivates it,waits until dna damage is fixed and then p53 levels drop,as do p21 levels and the cell cycle continues
what does damage to p53 and p21 lead to?
cancer (these are tumor suppressor genes)
what are p53 and p21
tumor suppressor genes
what is worse a single p53 or homozygous p53 mutation?
latter is far worse as no DNA damage will be detected
what are oncogenes?
accelerators of cell cycle progression e.g TF
what are tumour supressor genes?
inhibitors of cell cycle progression such as genes encoding p53 and RBP (retinoblastoma protein)
what are 3 examples of oncogenes?
genes encoding Ras, RTKs, Myc
