29_Cell Cycle II

Question 1

Where does Wee-1 phosphorylate cdc2 at?

Answer 1

Tyr-15

inhibitory effect

Question 2

What protein phosphorylates cdc2 at Thr-161?

Answer 2

CAK (cyclin activating kinase)

Question 3

What enzyme dephosphorylates cdc2 at Tyr-15? What is the result of this?

Answer 3

cdc24

Result: activation of the MPF and entry into mitosis

Question 4

Wee 1 is a (+/-) regulator and cdc25 is a (+/-) regulator of mitotic entry.

Answer 4

Wee 1: -

cdc25: +

Question 5

What do wee 1 mutants look like? Why?

Answer 5

They are small (wee). Since these cells cannot keep cdc2 in an inactive state, they divide prematurely (G2 is too short).

Question 6

Why can’t cdc25 mutants enter mitosis?

Answer 6

They cannot remove inhibitory phosphate from Tyr-15.

Question 7

How does proteolysis regulate CDK activity?

Answer 7

proteolysis of cyclins can be both an accelerator and brake

Question 8

How does subcellular localization of cyclins regulate CDKs?

Answer 8

accelerates (e.g. translocate to nucleus, and become ‘trapped’ there)

Question 9

Which cyclin’s levels oscillate the least?

Answer 9

Cyclin D

Question 10

What does pRB do in its activated state?

Answer 10

represses genes required for S phase

Question 11

During G1, what is E2F bound to?

Answer 11

pRB (and the gene promoter)

Question 12

What effect does CDK activation have on pRB?

Answer 12

pRB is phosphorylated => becomes inactive

E2F is released, and transcription is activated

Question 13

What class of proteins inhibit cyclin/CDK activity in early G1?

Answer 13

CDIs (cyclin-dependent kinase inhibitors)

Question 14

Which CDI family are binary inhibitors? Ternary?

Answer 14

Binary: INK4
Ternary: CIP/KIP

Question 15

Classify the CDIs p16 and p21 as members of INK4 or CIP/KIP.

Answer 15

INK4: p16

CIP/KIP: p21