Chapter 12 Cell Checkpoints Flashcards
What is the criteria for passing the G1 checkpoint?
- cell size is adequate
- nutrients are sufficient
- social signals are present
- DNA is undamaged
Why is the G1 checkpoint most important?
determines whether or not the cell will undergo another round of cell division
What is the criteria for passing the G2 checkpoint?
- chromosomes successfully replicated
- DNA is undamaged
What are the criteria for passing the M phase checkpoint?
- chromosomes have attached to spindle apparatus (end of prometaphase)
-chromosomes properly segregated (end of anaphase)
What two proteins work together to regulate cell cycle checkpoints?
cyclins and cdks
What are cyclins?
- amounts change throughout the cell cycle
- different types for different phases (ex: G1,G2, S, M)
- only present in large amounts when they are needed
What are CDKs?
- cyclin dependent kinases
- when they are activated by cyclins, they activate or inactivate other proteins to progress the cell cycle
- think phosphorylation (pushes cell cycle forward)
What is M Phase promoting factor (MPF)?
- cyclin B + CDK1
How is MPF regulated in interphase?
- cyclin B builds up and binds to the cdk
- the cdk is then phosphorylated at two sites (inhibitory and active sites)
How is MPF regulated at the G2 checkpoint?
phosphatase enzyme removes the inhibitory phosphate
How is MPF regulated at the M phase checkpoint?
the cyclin is degraded, inactivating the cdk1
What is the G1 checkpoint controlled by?
growth factors and tumor suppressors
What are growth factors?
-hormones that stimulate cell division
- polypeptides or small proteins
- “gas” of the cell cycle (tells it to proceed)
What are tumor suppressors?
- proteins that restrict cell division
- “brakes” of cell division
What are two G1 tumor suppressors?
- p53: DNA repair
- Rb (pRB): blocks S-phase