Checkpoint review

Question 1

What are the steps in the checkpoint that allows for dna replication? (S phase)

Answer 1

1. mitogens released to stimulate cell division 2. myc protein produced to increase production of g1 cyclins. 3. Rb inactivated by phosphorylation from cdk. 4. E2f activated, promoting formation of G1/s and s cyclins.

Question 2

What are the steps in the checkpoint that leads to the M phase?

Answer 2

1. Cdk Activating kinase adds phosphate group when M cyclins bind Cdk and Wee1 adds inhibitory phosphate group. 2. CDC 25 removes inhibitory phosphate to allow mitosis to proceed. 3. positive feedback loops inhibit wee1 and activate cdc25. 4. anaphase promoting complex activated and phosphorylated by m-cdk, causing destruction of mcdk.

Question 3

What are the steps of the metaphase anaphase transition?

Answer 3

Cdc20 binds and activates APC. 2. APC promotes activation of separase by degrading securin. 3. Causes break up of cohesin complex and separation of sister chromatids during anaphase.