Cell Cycle (Herschman)

Question 1

Three states that cells exist in regarding cell division

Answer 1

1) Always in cell cycle
2) Post-mitotic; never divide again
3) Resting; can be induced to divide

Question 2

Mitogen

Answer 2

Substance that will cause a resting cell (in G0) to re-enter cell cycle and divide

Question 3

When in cell cycle do you synthesize more histones?

Answer 3

S phase

Question 4

When does histone phosphorylation by His kinase occur?

Answer 4

Throughout cell cycle, with peak phosphorylation at the end of G2 and none by end of mitosis

Question 5

Proteins involved in G1-S transition

Answer 5

E2F: transcription factor that activates genes necessary for G1-S transition

RB (restriction boundary protein): normally is unphosphorylated and represses E2F, but when phosphorylated, doesn’t bind E2F (must be dephosphorylated again before next cell cycle)

Question 6

What is a double thymidine block?

Answer 6

Techinque to synchronize cells by causing them to accumulate at the G1/S interface

Question 7

Licensing factor

Answer 7

Factor in G2 cells that prevents the re-replication of already replicated DNA prior to mitosis

Question 8

What is checked for at G2/M checkpoint?

Answer 8

Make sure DNA is replicated and environment favorable for mitosis

Question 9

What is checked for at the S checkpoint?

Answer 9

Make sure DNA is not damaged and see if it can be repaired

Question 10

What is checked for at the M checkpoint?

Answer 10

Make sure all chromosomes attached to spindle

Question 11

M-phase promoting factor

Answer 11

Controls transition from G2 to M; is a cyclin-dependent kinase (cdc2) that must bind cyclin B in order to act; is specifically a histone kinase

Question 12

What is checked for at G1/S checkpoint (“Restriction Point”)?

Answer 12

Is environment favorable for DNA synthesis? If not, can go into G0.

Question 13

When does CDC2-Cyclin B act?

Answer 13

G2 to M

Question 14

When does CDK4-Cyclin D1 act?

Answer 14

Restriction point; this is what phosphorylates RB (thus allowing E2F to transcribe genes needed for S phase)

G1/S transition

Question 15

What does CDC2-Cyclin B do?

Answer 15

Phosphorylates histones (it is a histone kinase), so must contribute to chromatin condensation in mitosis

Question 16

After Cyclin B binds CDC2, what else must happen before the complex is active?

Answer 16

CDC2 must be dephosphorylated at 2 sites

Question 17

What are three ways to negatively regulate CDKs?

Answer 17

1) Phosphorylation at 2 sites makes the CDK inactive
2) CKI (cyclin dependent kinase inhibitor) can bind and inactivate CDK
3) Degrade the cyclin

Question 18

What is special about E3 enzyme in the ubituitination system?

Answer 18

E3 enzymes specifically target a certain protein for degradation

(ie E3 will degrade a specific cyclin at a specific point in the cell cycle)