cell cycle and controls Flashcards
what phase of the cell does replication happen?
S phase
what are the two divisions of M phase
mitosis and cytokinesis
where is the restriction point and what is its function?
the restriction point is at the end of G1. it is the point at which the cell surveys the environment to see if it is favoriable for division. once the cell gets the green light and passes the restriction point, it is commited to replication.
what happens if the environmental conditions are not favorable after the check at the restriction point?
the cell is sent into G0 where it stays and waits. The cell can remain in G0 for weeks or even years.
what is the acronym CDK mean and what is the relationship between cyclins and CDK during the cell cycle
CDK means cyclin dependent kinases. A lot of the events in the cell cycle requires kinases. CDK is dependent on cyclins to activate their kinase activity.
what are the four classes of CDKs?
G1 Cdk- promotes passage through restriction point
G1/S Cdk- commits cell to replication
S Cdk-initiates replication
M Cdk-promotes mitosis
what is the mechanism by which the cell switches off cyclin and Cdk activity?
it uses feedback mechanisms to turn off switches
which molecule controls initiation of replication
Cdc6
if Cdc6 is used in the S phase, why is its presence increased in early G1?
because towards the end of G1 is when the cell starts getting all the molecules together to execute the S phase
who are the members of the pre replicative complex (PRC) and how are they assembled?
Cdc6, ORC, and McM
Cdc6 binds to ORC which recruits McM which are the helicases need to do replication.
Cdc6’s job is to have the prereplication complex ready to do replication when the S phase starts
once the pre-RC complex is formed, how does the process of replication get activated?
Pre-RC is phosphorylated by S-Cdk but before S-Cdk can phosphorylate, it must first itself be turned on by S-cyclin
once replication has ended, how does the cell prevent itself from re replicating?
S-Cdk can actually phosphorylate Cdc6 which tags it for degradation. Without Cdc6, you cannot have assembly of Pre-RC and thus no replication can happen
what about after the cell goes through G2, how does it prevent rereplication then?
the cell maintains a high level of S-Cdk even in G2 that way they are always on guard to destroy Cdc6 and prevent rereplication.
M-Cdk also works to phosphrylate Cdc6 and McM (both members of the Pre-RC) making sure no replication happens
after one cell cycle, how does the cell reset itself to make sure it can go through another cycle in the new daughter cell?
At the end of mitosis (which is the last step of the cell cycle), ALL Cdk levels are reduced to zero resulting in dephosphorylation of Cdc6 and McM and allowing Pre-RC assembly to happen again
what is CAK? and what does it work analogous to?
CAK is the Cdk activating kinase which is like the cylcin from S phase cuz they both activate Cdk
who blocks M-Cdk and prevents it from doing work?
bitch ass Wee1. after CAK phosphorylates M-Cdk and activates it, Punk ass Wee1 can come around and also phosphorylate it and shutting it down. A M-Cdk with do P’s doesnt work.
after M-Cdk has been shut down by Wee1, who can come around and reactive?
Cdc25 can come around and take the second phosphate off and reactivate the M-Cdk
Wee1 can do its job shutting down M-Cdk but when M-Cdk get reactivated and gets going, theres no stopping it by Wee1, why?
Feedback mechanism of increase M-Cdk levels inhibit Wee1. M-Cdk also phosphorylates Cdc25, which causes it to work even harder DEphosphrylating more M-Cdk
once mitosis is over, how is M-Cdk inactivated?
M-Cdk cannot be inactivated, it must be degraded by ubiquitination
why are there no Cdk in G1 phase
well you dont want any division. but the actual degradation of Cdk is done by ubiquitination. the cell also keep a high level of CKI which is a cyclin kinase inhibitor.
how does the cell control Cdk on the treanscriptional level?
E2F is a transcription factor that makes Cdk. During G1, Rb binds to and inhibits E2F so no Cdk protiens are made. Until the cell recieves an external signal to dividethen G1-Cdk accumulates and phosphrylates Rb making it inactive and E2F can now do its job again
if the cell is damaged after G2, how does it prevent entry into mitosis?
If there is damage the cell blocks Cdc25 and thus prevents it from removing the inhibitory phosphate put on M-Cdk
how does p53 work are the gatekeeper of S phase?
it is there as the checkpoint after G1. It does so by increasing cellular CKI levels so S-Cdk cannot be activated and also with the help of p21
