Cell Division Flashcards
Lecture 6 + 7
What happens during interphase?
During interphase the chromatin is organised into loops. Cohesins and CTCF proteins define boundaries of the loops.
Define G1
The gap between M phase and S phase. Cell grows and makes a new set of organelles.
Define G2
The gap between S phase and M phase. Cell grows some more.
Define the S phase
The phase where the cell’s DNA and chromosomes replicate.
Define the M phase
This phase is Mitosis - the duplicated chromosomes split into identical daughter cells.
What happens at the checkpoints in the cell cycle?
Late G1 ‘start transition’ - the cell decides whether it will enter the S phase or not, depending on how well the DNA has been replicated.
G2 ‘n transition’ - cell gathers information on the DNA replication and whether the DNA is damaged or not. If the DNA is ok, the cell will enter M phase.
M phase ‘metaphase to anaphase transition’ - this checks whether the chromosomes are attached properly to the spindle fibres.
How are the checkpoints regulated?
The checkpoints are regulated by cyclin dependant protein kinases. Cyclins bind to the CDKs, activating them.
There are different CDKs used throughout the cell-cycle and the levels of each fluctuate throughout the cycle
What do kinases do?
A kinase is an enzyme that phosphorylates proteins to either activate or deactivate them therefore regulating the cell cycle.
Outline the mechanism of the CDK-activating kinases (CAKs)
Binding of cyclin does not fully activate the CDK so it needs to be phosphorylated to be fully activated. There is a loop on the active site of CDK called the T-loop.
When cyclin binds to the CDK, it causes the T-loop to fold partially so it is not fully activated.
When phosphate binds to the T-loop, it causes it to completely fold and therefore leading to the CDK being fully activated.
Outline the mechanism of Wee1-Cdc25
