The Eukaryotic Cell Cycle

Question 1

The cell cycle is a sequence of ordered events controlled by master regulators called ________.

Answer 1

Cyclin Dependent Kinases (CDK)

Question 2

The key regulatory subunit of CDKS are called ______.

Answer 2

Cyclins.

Question 3

Describe the positive regulators of the cell cycle.

Answer 3

Each cyclin acts at a specific stage of the cell cycle and sets up the transition to the next stage, then gets degraded.

Question 4

Describe negative regulators of the cell cycle.

Answer 4

Surveillance mechanisms that check for the proper progression through the cell cycle. If something goes wrong, these checkpoints hold the cycle until the repair is done.

Question 5

The decision to divide is highly controlled at what stage of the cell cycle?

Answer 5

G1.

Question 6

G1 + S + G2 = ??

Answer 6

Interphase

Question 7

Describe checkpoints in the context of the cell cycle.

Answer 7

Act ask brakes on the cell cycle progression when event are not completed or when DNA is damaged.

Question 8

Describe the spindle assembly checkpoint.

Answer 8

Are all chromosomes attached to the mitotic spindles?

Question 9

Describe the chromosome segregation checkpoint.

Answer 9

Have all the chromosomes reached opposite poles?

Question 10

In what phase of the cell cycle are G1/S phase CDKs activity the highest?

Answer 10

G1/S phase

Question 11

In what phase of the cell cycle are S phase CDKs activity the highest?

Answer 11

S/G2 phase

Question 12

In what phase of the cell cycle are Mitotic CDKs activity the highest?

Answer 12

G2/Mitosis

Question 13

Budding or Fission Yeasts are model organisms of studying the cell cycle. Why?

Answer 13

• Unicellular organisms
• Easy to grow and synchronize
• Rapid cell cycle (2-4 hours)
• Cell cycle stage visualized by the morphology of the cell
• Can be grown as haploid cells (easy genetics)
• Condition loss of function mutants display distinct morphology

Question 14

List morphological differences of cells at the different stages of the cell cycle in budding yeast.

Answer 14

• Spindle pole body duplication at the start
• Bud emergence at the end of the G1 phase
• Spindle formation and nuclear migration in between the S and G2 phase

Question 15

Describe the way in which cell synchrony can be used to study the cell cycle. Include yeast cells and mammalian cell culture.

Answer 15

Yeast Cells:
- Mating pheromone arrests cells in the late G1
- Nocodazole disrupts mitotic spindle and cells arrest in pro-metaphase

Mammalian Cell Culture:
- Hydroxyurea of thymidine inhibit the synthesis of dNTPs and cells arrest in early S phase
- Nocodazole disrupts mitotic spindle and cells arrest in pro-metaphase

WASHING AWAY THE AGENT ALLOWS FOR SIMULTANEOUS PROGRESSION OF ALL CELLS THROUGH THE CELL CYCLE

Question 16

Describe the process of flow cytometry and measuring the amount of cellular DNA.

Answer 16

1. Fix cells by Ethanol
2. Degrade all RNA
3. Soak the cells with a DNA staining dye
4. Wash all cells
5. Run cell suspension through a capillary tube, one cell at a time
   6.Use lasers to detect the amount of stain (indirect measure of the amount of DNA) in each cell
6. Plot the results

Question 17

Isolated temperature sensitive (ts) mutants not growing at restrictive temperature (arrest with certain morphology). At what temperatures will yeast treated with a mutagen grow and replicate.

Answer 17

Permissive temperatures (23 degrees Celsius). Ts mutants will not grow at restrictive, higher temperatures.

Question 18

Describe the trend of cyclin levels in the cell cycle. This protein is continually synthesized and periodically destroyed in the cel cycle.

Answer 18

Cyclin levels rise during interphase, peak at mitosis, and drop before anaphase. Cyclin destruction occurs just prior

Question 19

Which cyclin regulates CDK1?

Answer 19

Cyclin A and Cyclin B

Question 20

Which cyclin regulates CDK2?

Answer 20

Cyclin A and Cyclin E

Question 21

Which cyclin regulates CDK4?

Answer 21

Cyclin D

Question 22

Which cyclin regulates CDK6?

Answer 22

Cyclin D

Question 23

Which cyclin is the G1 cyclin? What does it regulate?

Answer 23

Cyclin D regulates CDK4/6

Question 24

Which cyclin the G1/S cyclin? What does It regulate?

Answer 24

Cyclin E regulates CDK2.

Question 25

Which cyclin is the S cyclin? What does it regulate?

Answer 25

Cyclin A regulates CDK2.

Question 26

Which cyclin is the M cyclin. What does it regulate?

Answer 26

Cyclin B regulates CDK1.

Question 27

Describe the function of the G1 cyclin (D).

Answer 27

• Coorindate entry into a new cell cycle in response to growth factors.
• Inactivate CDK inhibitors allowing the activation of G1/S cyclins

Question 28

Describe the function of the G1/S phase cyclin (E).

Answer 28

-Inactive inhibitors (Rb) of entry into S-phase.
- Stimulate synthesis of genes controlling S phase including cyclin A

Question 29

Describe the functions of S cyclins (A).

Answer 29

• Irreversibly initiate DNA replication.