Control of Cell Proliferation Flashcards
Cell numbers must be controlled:
Control involves ….. ………….., …….. …….. ……… and …………. ………..
cell communication
cell-cell contacts, growth factor signals
What is the cell cycle?
What does it involve?
Why is important?
- the processes of growth and division
- involves checkpoints and feedback control
- important for maintenance of genome integrity
and symmetrical cell division
What are the 4 phases of the cell cycle?
G1 - growth, preparation for DNA replication
S - replication of DNA
G2 - growth,
M - mitosis
What are G1, S and G2 collectively known as?
interphase
Define a checkpoint
A critical control point in the cell cycle where stop and go-ahead signals regulate the cell cycle
In what phases do they 3 prominent checkpoints take place?
G1 checkpoint
G2 checkpoint
Metaphase checkpoint
Describe the G1 checkpoint.
What is it checking for?
How does it do this?
The Restriction Point
- ensures cell is large enough to divide
- if receives go ahead, will continue with cell cycle
- if no signal, it will exit the cycle and switch to G0 (a non dividing state)
Which phase are most cells in the human body in?
G0 i.e. a non dividing state
Describe the G2 checkpoint
ensures that DNA replication in S phase has been completed successfully
Describe the metaphase checkpoint
ensures that all of the chromosomes are attached to the mitotic spindle by a kinetochore
Which enzymes regulate the cell cycle?
How?
cyclin dependent kinases
fluctuations in the abundance and activity of cyclins and CDK’s pace the events of cell cycle
What is a kinase?
Where do they act in the cell cycle?
An enzyme which activates of deactivates a protein by phosphorylating it
Kinases give the go-ahead single at the G1 and G2 checkpoint
How are CDK’s activated?
cyclins accumulate during the G1, S and G2 phases of the cell cycle, binds to CDK’s
What does mCDK regulate and how?
Regulates mitosis
Enough cyclins available by the G2 checkpoint to form complexes which initiate mitosis (by phosphorylating key proteins in the mitotic sequence)
Later in mitosis, mCDK switched off by initiating a process that destroys cyclin
New cyclin is synthesised during the next interphase
What role does pRB have in the cell cycle?
Retinoblastoma protein
Regulates G1 checkpoint
In the absence of GF’s pRB binds to transcription regulators of genes for cell proliferation, prevent continuation of the cell cycle
Growth factors large surface receptors activating CDK’s which phosphorylate pRB, causing it to release its binding of transcription factor regulators. These activate genes for cell proliferation