Cell Cycle

Question 1

Go

Answer 1

The phase that can be entered from G1 in which the cell loses its cell cycle machinery. Either Senescence or Quiescence

Question 2

The three checkpoints in the cell cycle

Answer 2

1. G1 checkpoint (to enter into S phase only if environment is favorable)
2. G2 checkpoint (to enter M phase only if environment is favorable and all DNA is replicated)
3. Metaphase checkpoint (if all chromosomes are attached to the spindle/microtubules)

Question 3

Mitogen

Answer 3

similar to a growth factor, some molecule needed to go from phase to phase in the cell cycle

Question 4

Cdk

Answer 4

a protein kinase that is cyclin dependent. Without cyclin, the Cdk is inactive

Question 5

Three types of Cdk

Answer 5

G1/S Cdk present with G1/S cyclin before S phase
S Cdk present with S cyclin at the start of S phase
M Cdk present with M cyclin in late G2 but active at the start of mitosis

Question 6

CAK

Answer 6

Cdk Activating Kinase- Cdc25- phosphorylates Cdk so that it is activated and can interact with cyclin to progress through the cell cycle

Question 7

Wee 1 kinase

Answer 7

an inhibitory phosphatase that adds two phosphates to Cdk to inactivate it-cell cycle is paused

Question 8

M/Cdk assembly and activation process (same for G1/S process

Answer 8

Cdk 1 and M cyclin join, they are phosphorylated by both CAK and Wee 1 to be inactive, and then a phosphorylated/active Cdc25 will remove two phosphates to activate Cdk1/Mcyclin.

Question 9

APC

Answer 9

Anaphase promoting cyclase- a ubiquitin ligase which degrades M cyclin

Question 10

SCF

Answer 10

ubiquitin ligase that degrades M cyclin

Question 11

Rb

Answer 11

a protein that binds the E2F transcription factor. When Rb is phosphorylated, E2F is released and and upregulates genes needed for S phase (occurs in G1 and encouraged by G1/s Cdk)

Question 12

Proteins that E2F promotes transcription of

Answer 12

G1/S cyclin (cyclin E) and S cyclin (cyclin A)

Question 13

What do viral proteins do with respect to Rb?

Answer 13

viral proteins bind Rb to allow E2F free. This promotes of transcription of S phase genes so that virus can replicate with the help of the host.

Question 14

p53

Answer 14

“Guardian of the Genome”. With too much DNA damage, p53 promotes apoptosis. With mini damages, p53 promotes p21 transcription. Regulated by a ubiquitin ligase that dissociates when p53 is phosphorylated

Question 15

p21

Answer 15

a CKI (cyclin kinase inhibitor) activated by p53 which inhibits G1/Cdks and cyclins from ~P E2F free from Rb