cell cycle Flashcards
DEFINE: cell cycle clock
network of interacting proteins in the nucleus that receives signals from outside and inside the cell, integrates them and decides the cell’s fate
how does excessive proliferation occur?
- produce growth factors by themselves —-> autocrine stimulation of cell proliferation
- stimulate normal cells to produce growth factors
- deregulate downstream signalling of growth factor
> overexpress GF receptors
> ligand independent firing - inhibit negative feedback mechanisms that control proliferative signalling
how long does G1 last?
8-10 hours
how long does S phase last?
6-8 hours
what are some methods used to study the cell cycle?
- flow cytometry
- immunofluorescence and epifluorescence microscopy
describe how flow cytometry is used to study the cell cycle
- treat cells with fluorescent dye
- more fluorescence = more DNA present
- DNA content doubles during S phase so intensity of fluorescence also doubles
- cells in G0 or G1 have half the fluorescent signal as cells in G2 or M phase
describe how immunofluorescence
is used to study the cell cycle
- label microtubules using primary and secondary antibodies conjugated to a fluorophore
- observe changes in organisation of microtubules during the different phases of mitosis
- cells during different phases of mitosis will have different morphology
describe how epifluorescence is used to study the cell cycle
- stain cells with nuclear staining = epifluorescence
- observe changes in organisation of DNA during the different phases of mitosis
- cells during different phases of mitosis will have different morphology
there is a window of time for the cell to consult the extracellular environment on a decision to proceed with cell division or not. what is it?
start of g1 to 1-2 hours before g1-to-s phase transition
what are the targets of CDK?
- centrosome associated proteins promoting centrosome duplication
- proteins controlling dna replication that are activated by phosphorylation
what do cyclins do?
associate with cdk and increase the catalytic activity of cdk
helps with substrate recognition –> cdk phosphorylates correct target
what does MPF do?
induces cell entry into m phase
binds cyclin B to cdc2
phosphorylates cdc2
linked to protein kinase activity which oscillates throughout the cell cycle
which cdks form a complex with cyclin d?
cdk4/6
which cdk forms a complex with cyclin e?
cdk2
which cdk forms a complex with cyclin a
cdk2
then cdk1/cdc2
which cdk forms a complex with cyclin b?
cdc2/cdk1
which cdk forms a complex with cyclin c?
cdk3
what is the decrease in cyclin levels throughout the cell cycle mediated by?
ubiquitination-dependent degradation
which cyclin/cdk complexes can INK4 CKIs inhibit?
cyclin d + cdk4/6 only
what are the INK4 proteins?
p16INK4A
p15INK4B
p18INK4C
P19INK4D
which cyclin/cdk complexes can kip CKIs inhibit?
all other cyclin/cdk complexes aside from cyclin d/cdk4.6
what are the kip proteins?
p57Kip2
p27Kip1
p21cip1
what is the role of TGFβ signalling during the EARLY stages of tumourigenesis?
arrests growth of a variety of cell types
what is the role of TGFβ signalling during the LATER stages of tumourigenesis?
promotes tumour invasiveness and formation of metastases
how does TGFβ control the cell cycle?
- strongly increases expression of p15INK4B -> cells do not reach R point –> blocks proliferation
- weakly induces p21Cip1 upon dna damage –> cell cycle halted until genome is repaired
- inhibits myc expression + prevents myc from binding cki promoters
how do growth factors control cell cycle progression?
- growth factor binds to receptor
- PI3K pathway activated
- Akt/PKB activated
- Akt phosphorylates p21Cip1
- phosphorylated p21Cip1 translocates to cytoplasm so cannot inhibit cyclin/cdk complexes
what is the kaplan meir survival curve?
non-parametric statistical method used to estimate survival function
