Cell Cycle Control

Question 1

What are the 4 phases of cell cycle control ?

Answer 1

M - Mitosis
G1 - Gap1
S - Synthesis
G2 - Gap2

Question 2

What is the Cdc 2 ?

Answer 2

The master cell cycle regulator

Question 3

What is cdc25 required for?

Answer 3

G2/M

Question 4

Wee mutants can’t delay ?

Answer 4

Cell cycle and divide small

Question 5

what is cdc2 required for ?

Answer 5

Both G1/S and G2/M

Question 6

cdc2 mutants can be either?

Answer 6

Cdc or wee

Question 7

Cdc2 was identified in ?

Answer 7

A mutant screen in fission yeast as required for entry into mitosis

Question 8

Cyclins were identified as?

Answer 8

Proteins that varied in a cyclical fashion during the cell cycle. Expressed and destroyed each cell cycle

Question 9

What is a Mitosis-promoting factor (MPF) ?

Answer 9

This is a cell cycle control element able to cause metaphase when injected into amphibian oocytes or when incubated with nuclei in a cell-free system

Question 10

MPF is a complex between?

Answer 10

A 34kD serine/threonine protein kinase, identified as a Xenopus homolog of the cdc2 gene product, p34cdc2, and a 45kD substrate, identified as a Xenopus B-type cyclin

Question 11

What is Cdc2 ?

Answer 11

This is a cyclin-dependent protein kinase (CDK)

Question 12

Cdk regulation ensures ?

Answer 12

Ordered progression through the cell cycle

Question 13

Once cells are in cell cycle what happens ?

Answer 13

The cells are ‘licensed’ to go through S phase once in a cell cycle

Question 14

Cells can only enter S phase from ? and what is blocked ?

Answer 14

Cells can only enter S phase from G1 re-replication is blocked

Question 15

What is meant by Licensing?

Answer 15

Loading of replicative helicase

Question 16

CDK activates ?

Answer 16

Replication initiation

Question 17

What does licensing prevent ?

Answer 17

Re-replication

Question 18

Explain the steps Cdk, S-cyclin, S-Cdk ?

Answer 18

1. Low Cdk activity. Loadinf of licensing factor at origins
2. S-cyclin increases
3. S-Cdk activates replication
4. S-Cdk activity high. No licensing
5. M-cycin increases
6. M-Cdk activated triggers mitosis
7. Cyclin destroyed resetting cycle

Question 19

What is meant by Checkpoints ?

Answer 19

Cells delay cell cycle progression in response to external signals, DNA damage

Question 20

What are the Major transition points or checkpoints in interphase:

Answer 20

• START. Cells are licensed in G1 to enter S phase

Question 21

Cells proceed through the cell cycle in one direction. This is controlled by ?

Answer 21

Cell division kinases, Cdks (cdc2 = CDK1)

Question 22

Cdks form a complex with?

Answer 22

Cyclins which are periodically expressed and destroyed

Question 23

The CDK/cyclin complex is kept inactive by ?

Answer 23

Wee1 until it is activated by Cdc25