Cell Cycle Control and Cell Division I Flashcards
Which of the following is NOT a checkpoint control in the cell cycle?
M/G1
metaphase to anaphase
Late G1
G2/M
M/G1
ratio of people that get cancer:
1 in 3
What is cancer?
uncontrolled cell growth
-inappropriate proliferation
what are the three checkpoints if the cell cycle?
start checkpoint (G1)
G2/M checkpoint
metaphase-anaphase checkpoint
what does the G1 checkpoint check for?
-nutrients
-growth factors
-DNA damage
what does the G2/M checkpoint check for?
-cell size
-DNA replication
what does the metaphase-anaphase checkpoint check for?
chromosome spindle attachment
What three things does the cell cycle checkpoint control system depend on ?
-cyclically activated cyclin-dependent protein kinases
-cyclical proteolytic events
-transcriptional regulation
What happens if the cell fails to complete an essential cell-cycle process?
the cycle arrests
What does Cdk require?
the binding of cyclin and subsequent phosphorylation to become an active enzyme
When is Cdk in an inactive state?
when there is an absence of cyclin
What are the three steps of Cdk?
- cyclin binding
- phosphorylation
- activation
what is G1 cyclin?
cyclin D
what Cdk is cyclin D associated with?
Cdk4/6
what is G1/S cyclin?
cyclin E
what Cdk is cyclin E associated with?
Cdk2
what is S cyclin?
cyclin A
what Cdk is cyclin A associated with?
Cdk2/1
what is M cyclin?
cyclin B
what Cdk is cyclin B associated with?
Cdk1
How many major cyclins are in the cells?
4
cyclin D, E, A, and B
does the concentration of Cdks change?
no
What does the changing of cyclins being expressed allow?
promote transition through the cell cycle
What initiates the metaphase to anaphase transition?
anaphase-promoting complex (cyclosome) APC/C
Where does the cyclin complex get phosphorylated?
the T loop at a threonine residue
What further regulates the cyclin-Cdk activity?
Wee1 kinase
What does Wee1 kinase do?
phosphorylate Cdk and renders it inactive
*adds a second inhibitory phosphate
what does Cdc25 phosphatase do?
dephosphorylates inactive cyclin-Cdk and restores activity
What is anaphase-promoting complex (cyclosome)?
member of ubiquitin ligase family of proteins
-catalyzes the ubiquitylation and degradation of securin and the S and M cyclines
What is securin?
protein involved with protecting the protein linkages that hold the sister chromatids together
What does securin degradation do?
leads to activation of a protease that then separates the sisters and unleashes anaphase
What does degradation of S and M cyclins lead to?
inactivation of Cdks
What does loss of Cdks mean?
their targets can be dephosphorylated by various phosphatases that are present in anaphase
When is APC/C activated?
in mid-mitosis and remains active in G1
When G1/S-Cdks are activated in late G1…
APC/C is turned off
*allows for accumulation of cyclin needed to start the next cell-cycle
what needs to bind to APC/C to activate it?
Cdc20
What is SCF?
ubiquitin ligase like APC/C
How many subunits of SCF?
3
What does SCF do?
ubiquitylates Cdk inhibitor proteins in late G1 such as p27
What does ubiquitylation of proteins do?
marks proteins for degradation
what is p27?
member of the CKI family that binds to activated cyclin-Cdk complex and distorts the active site of the Cdk inhibiting the enzyme activity
What is an F-box protein?
a protein that associates with SCF that is required for binding to specific protein targets
When is the G1-Cdk active?
in G1
When is G1/S-Cdk active?
in G1
When is S-Cdk active?
transition between G1 to synthesis
When is M-Cdk active?
before mitosis
What is the G0 phase?
resting or quiescent state
-cells can remain for days to weeks or longer
-can enter this until cell dies
When does a cell typically enter G0?
when there is a lack of growth factors or nutrients
What does the dREAM complex bind to?
deacetylated histone H4
What phase is the dREAM complex associated with?
G0
