13.1 Cell Cycle control II Flashcards
How do negative feedback loops result in oscillations of protein activity?
Activating kinase protein phosphorylates itself as well copies of itself. Phosphorylation causes the protein to be active and builds up the protein. The inhibitor of this protein is also slowly activated by the same kinase protein. Activation is slow but once it is activated, it shuts off the kinase efficiently.
In G1, cyclin gene expression is high/low?
Low
The APC can be thought of as _________ for M-phase kinase activity.
An “off” switch
Active APC targets ______ and ______ phase cyclins for degradation.
S and My but not G1/S cyclins
During G1 phase, there is essentially no _______ activity.
Cdk activity
Input from _______ drive the cell into the cell cycle.
Mitogens
CKI keeps the cell in _____ phase so it’s destruction allows the cell to move to ______ phase.
G1 phase
S phase
During S phase, M-Cdk is held in an inactive state by ________.
CKI
When M-Cdk levels get high enough, what happens?
There is a sudden and dramatic activation of M-Cdk through the function of 2 feedback loops. One inactivates the inhibitor of M-Cdk and one activates an activator of M-Cdk.
M-Cdk phosphorylates cdc20 during what stage of the cell cycle?
Late M phase
APC inhibits the activity of _________.
G1/S, S and M cyclin expression in the late M phase
An increase in APC activity brings about the end of ______ and the start of _______.
End of mitosis
Beginning of G1 phase
How can cells prolong G1 phase?
- Use of an alternate activator of APC, called Cdh1 (non-embryonic cells)
- Use of M-Cdk inhibitor called Sic1
What happens to turn off the APC in G1?
G1/S-Cdk activity inactivates the APC complex. This, along with degradation of Cdk inhibitors, turns off all inhibitors keeping the cell in G1 phase.
Why is G1/S-Cdk activity the first to get started when the cell enters the cell cycle?
When the cell transitions the cell cycle, mitogens bind to the cell surface receptors and stimulate the transition and G1/S-cyclin and S-cyclin genes are expressed.
What stage of the cell cycle do M-cyclins begin to be expressed?
M-cyclin genes are no longer repressed when the cell moves into the G2 phase so that is when the M-cyclin levels start to rise.
What does Mcm helicase do?
Use ATP to unwind DNA during S phase. The Mcm proteins bind to the origin of replication in order for DNA replication to occur.
The cell must only replicate DNA once during the ______ phase.
S phase
