13.1 Cell Cycle Control II Flashcards
How does negative feedback result in oscillations of protein activity?
A Kinase protein will phosphorylate itself as well as other copies of itself in a course downstream targets. This phosphorylation makes individual proteins more active.
Once the proteins have been activated they phosphorylate all other copies of the protein more rapidly. (you see a sharp rise in the activity of the kinase.
This will slowly begin to activate its inhibitor until it reaches a point where there is more active inhibitor than active kinase.
Kinase falls rapidly and since it is no longer activating the inhibitor, the inhibitor also slowly falls as its phosphates are hydrolyzed.
once the inhibitor activity has fallen to some base level the process repeats
How is expression of cyclins and APC in the G1 phase?
expression of m and s cyclin is low and APC activity which began in meta/anaphase transition is high.
Why is expression of cyclin low in G1 phase?
1) Cyclins is low b/c transcription factors regulating the expression of these cyclins are inhibited
2) Active APC is targeting S and M phase cyclins for degradation but not G1/S cyclins
3) there is a high level of active CDK inhibitor that is important for keeping CDK activity down even if a small amount of the cyclins get expressed.
What activity is not present in G1 phase?
NO CDK activity in G1 phase and there is no S or M phase cyclin activity. APC does not inhibit G1/S CDK so this is active in G1
How is G1/S of cell cycle initiated?
by control of signaling systems which are regulated by the binding factors called mitogens to the cell surface receptors.
What are mitogens?
Mitogens are factors that drives cell into the cell cycle
Which cyclins are present in G1/S phase? Which one becomes functionally active in G1/S?
G1/S cyclin and S Cyclin are expressed S is not expressed till mid G1.
Initially, the activity of APC is still active and it is still targeting S-cyclin for degradation and the inhibitors of S and M phase cyclins are still around so the only CDK that becomes functionally activated is G1/S CDK.
In G1/S phase what is anaphase promoting complex doing? is it active or inactive?
Active in the beginning but then when G1/S CDK becomes functionally activated it will inactivate the APC complex and also targets the CDK inhibitors for degradation
What turns off all the inhibitors that are keeping the cell in G1?
The activity of G1/S CDK
What results from the activity of G1/S-Cdk?
activity of all inhibitors turn off and all S-CDK levels start to go up
What leads to the suppression of gene expression of G1/S cyclin?
G1/S-CDK activates proteins that degrade G1/S cyclins and that ends up suppressing gene expression of G1/S cyclin as the cell goes into S phase.
What drives the cel into S phase?
The rise of S-CDK activity drives the cell into S phase
In S phase how are the levels of G1/S cyclin? What about APC?
G1/S cyclin levels go down and APC is low b/c it was turned off and there is nothing to turn it back on.
What is the SFC complex ?
SFC complex targets a CDK inhibitor for degradation, which is important for keeping cells in G1.
What allows the cell to move forward into the S phase?
Destruction of the CDK inhibitor by SFC allows the cell to move forward into S phase
