12.2 Cell Cycle Control I

Question 1

If you looked at the amount of DNA in each cell of a population of randomly growing cells, what sort of graph would you get?

Answer 1

A graph of the amount of 2N, 4N or in between amounts of DNA with distributions depending on what proportions of cells were in different stages of the cell cycle at that time. The amount of DNA per cell increases from 1N to 4 N from phase G0 to G2 on the x-axis.

Question 2

What is BrdU staining?

Answer 2

BrdU is a man-made chemical form or thymidine that can be used in place of thymidine in the cell replication cycle so you are able to detect the amount of cells that are dividing in tissue.

Question 3

What are the locations of the cell cycle checkpoints?

Answer 3

Between G1/S, G2/M and between Metaphase and Anaphase

Question 4

Regulators of the cell cycle are __________.

Answer 4

Cyclin dependent kinases

Question 5

What activates cyclin dependent kinases (Cdk)?

Answer 5

Cyclin proteins activate Cdk proteins. Without Cyclin, Cdk is inactive.

Question 6

What are the 2 mechanisms that inhibit the function of Cdk?

Answer 6

1. Wee1 kinase protein adds phosphate groups to the Cdk inactivating it
2. Cdk inhibitor proteins (such as p27) bind to the Cdk/cyclin complex and therefore inactivates it

Question 7

Wee1 and cdc25

Answer 7

Wee1 phosphorylates Cdk proteins causing it to be inactive. Cdc25 does the reverse, dephosphorylating Cdk and re-activates it

Question 8

CKI p27

Answer 8

Inhibit the function of Cdk where it binds to the cyclin/Cdk complex and prevents its normal function.

Question 9

What is the pathway that leads to separation of sister chromatids in Anaphase?

Answer 9

The degradation of the securin protein on the securin/separate complex by use of the cdc20 activation of the APC protein pathway

Question 10

How is mitosis turned off at the Metaphase/Anaphase transition?

Answer 10

By an active APC/cdc20 complex that promotes degradation of the Cdk protein complex.

Question 11

What is the role of ubiquitin ligases E1 and E2?

Answer 11

They are attracted to the Cdk/cyclin complex in order to synthesize a ubiquitin chain that will attach to the protein in need of being degraded.

Question 12

How many classes of cyclin proteins are there?

Answer 12

4 classes:

G1, G1/S, S and M

Question 13

How many Cdk proteins are there in the cell cycle?

Answer 13

4, one for each of the classes of cyclins