Cell Cycle Control Flashcards
What are the 4 phases of cell cycle control ?
M - Mitosis
G1 - Gap1
S - Synthesis
G2 - Gap2
What is the Cdc 2 ?
The master cell cycle regulator
What is cdc25 required for?
G2/M
Wee mutants can’t delay ?
Cell cycle and divide small
what is cdc2 required for ?
Both G1/S and G2/M
cdc2 mutants can be either?
Cdc or wee
Cdc2 was identified in ?
A mutant screen in fission yeast as required for entry into mitosis
Cyclins were identified as?
Proteins that varied in a cyclical fashion during the cell cycle. Expressed and destroyed each cell cycle
What is a Mitosis-promoting factor (MPF) ?
This is a cell cycle control element able to cause metaphase when injected into amphibian oocytes or when incubated with nuclei in a cell-free system
MPF is a complex between?
A 34kD serine/threonine protein kinase, identified as a Xenopus homolog of the cdc2 gene product, p34cdc2, and a 45kD substrate, identified as a Xenopus B-type cyclin
What is Cdc2 ?
This is a cyclin-dependent protein kinase (CDK)
Cdk regulation ensures ?
Ordered progression through the cell cycle
Once cells are in cell cycle what happens ?
The cells are ‘licensed’ to go through S phase once in a cell cycle
Cells can only enter S phase from ? and what is blocked ?
Cells can only enter S phase from G1 re-replication is blocked
What is meant by Licensing?
Loading of replicative helicase
CDK activates ?
Replication initiation
What does licensing prevent ?
Re-replication
Explain the steps Cdk, S-cyclin, S-Cdk ?
- Low Cdk activity. Loadinf of licensing factor at origins
- S-cyclin increases
- S-Cdk activates replication
- S-Cdk activity high. No licensing
- M-cycin increases
- M-Cdk activated triggers mitosis
- Cyclin destroyed resetting cycle
What is meant by Checkpoints ?
Cells delay cell cycle progression in response to external signals, DNA damage
What are the Major transition points or checkpoints in interphase:
- START. Cells are licensed in G1 to enter S phase
Cells proceed through the cell cycle in one direction. This is controlled by ?
Cell division kinases, Cdks (cdc2 = CDK1)
Cdks form a complex with?
Cyclins which are periodically expressed and destroyed
The CDK/cyclin complex is kept inactive by ?
Wee1 until it is activated by Cdc25
