Problem Set 7

Question 1

If a yeast cell in G1 in moved from rich medium to a low nutrient medium, the cell will likely..

Answer 1

Stay in G1 longer until it reaches the normal size to enter S phase

Question 2

What controls the phosphorylation events that regulate the cell cycle?

Answer 2

The action of a kinase that requires bound cyclin for its activity

Question 3

Once the signal that directs a cell to move from G1 to S phase has been generates, what does the cell do?

Answer 3

the cell replicates its DNA

Question 4

When G1 phase cells are S phase cells are fused together, the G1 nucleus begins to replicate DNA. What can be drawn from this result?

Answer 4

S phase cytoplasm contains diffusible factors that stimulate the initiation of DNA synthesis

Question 5

As concentrations of cyclin increases in the cell,

Answer 5

CDK binds the cyclin subunit and is activated

Question 6

What do CDKs do just before the end of G2 to initiate the events leading to mitosis?

Answer 6

Phosphorylate substrates needed for cell to enter mitosis

Question 7

In addition to cyclin, what else contributes to CDK activation?

Answer 7

Phosphorylation at an activating site on the CDK and the removal of an inhibitory phosphate group from CDK

Question 8

What leads to a halt in the progress of the cell cycle?

Answer 8

When chromosomal DNA damaged and when DNA replication is not completed

Question 9

What kind of interaction attacked polyubiquitin to the target protein?

Answer 9

Covalent interactions

Question 10

What would be likely to happen to yeast cells in G1 if you were able to treat them with an inhibitor that specifically inactivated its only CDK?

Answer 10

The cells would remain in G1 and would not progress toward mitosis

Question 11

The catalytic subunit of maturation-promoting factor…

Answer 11

transfers a phosphate group from ATP to certain a.a of specific substrates
AND
converts ATP to ADP

Question 12

If you made a temp sensitive mutation that made mammalian CDK1 inactive at 42.C, what would happen to the cells at 42.C?

Answer 12

They would be stuck in G2 with replicated DNA

Question 13

If you made a temp sensitive mutation that inactivated cyclin D at 42.C, what would happen to the cell at 42.C?

Answer 13

they would accumulate at G1

Question 14

If you made a temp sensitive mutation in CDK2, what would happen to the cells when you shift to the restrictive enzyme?

Answer 14

they would be stuck in G1 or S phase

Question 15

assume CAK normally does not phosphorylate CDK until Wee1 has added its phosphate. if you made a temp sensitive mutation in yeast that made CAK able to phosphorylate CDK at any time at restrictive temp, what would happen?

Answer 15

They would be smaller than normal

Question 16

Cdc25 is normally regulated by nutritional and other environmental factors to allow activation of cyclin/cdk at appropriate time. if you made a mutation in yeast Cdc25 that removed this regulation and made the enzyme always active at the restrictive enzyme, what would be the response?

Answer 16

The cells would be unusually small

Question 17

if you made a temp sensitive mutation in Wee1 kinase that made the enzyme hyperactive at the restrictive temp, what would be the result?

Answer 17

the cells would be unusually large

Question 18

if you made a mutation that knocked out Cdc25 function, what would happen to the cells?

Answer 18

The cells would grow abnormally large

Question 19

The stage that is not in the cell cycle is…

Answer 19

Go

Question 20

The stages of the cell cycle that are included in interphase

Answer 20

G1, S, and G2

Question 21

The stage of the cell cycle in which proteins needed for cell division would likely be made is…

Answer 21

G2

Question 22

You observe a cell line growing on a culture dish. The cells cover the entire surface of the dish and cell division ceases. You scrape and remove a circle of cells from the center of the disk. Cells bordering the cell start dividing and running through what appears to be a normal cell cycle. What phase of the cycle were they in before the circle of cells were removed?

Answer 22

Go

Question 23

What triggers the entry of a cell into mitosis?

Answer 23

the removal of inhibitory phosphate group from Cdk by Cdc25 phosphatase

Question 24

During degradation of the specified protein…

Answer 24

ubiquitin protein ligases mediate addition of ubiquitin chains to cyclins and APC/C recognizes a conserves destruction box seq in mitotic cyclins and promotes their polyubiquitin

Question 25

The stages of the cell cycle in which chromosomes are at least partially doubles..

Answer 25

G2, S, M

Question 26

Stage of the cell cycle in which chromosomes are doubles for the whole stage

Answer 26

G2

Question 27

_____ is a lipid kinase that interacts with growth factor receptors and triggers signaling cascades that influence all cell growth, while ___ is a protein kinase that phosphorylates targets that act to increase protein synthesis

Answer 27

P13-kinase

mTOR

Question 28

the proteasome…

Answer 28

removes misfolded or damaged proteins, controls the amount of cyclin proteins, and degrades ubiquitin proteins

Question 29

Covalent associations between proteins are rare in cell biology, but one exception is…

Answer 29

addition of ubiquitin to other cellular to other cellular proteins

Question 30

how can one ID a specific gene mutated in a strain

Answer 30

introduce plasmids into the yeast to express genes from a normal yeast

Question 31

a grad student notices as he microinjects an antibody that specifically recognizes cyclinD into mammalian cells that DNA replication doesn’t occur. Why does this happen?

Answer 31

antibody blocks the activity of cyclinD

Question 32

what conclusions have been made about functioning maturation-promoting factor?

Answer 32

progression of cells into mitosis depends on an enzyme whose activity is to phosphorylate other proteins and MPF activity is controlled by a subunit whose conc varies from one cell type to another