Q: Which of the following equations correctly represents the composition of MPF?

$$\text{MPF} = \text{Cyclin} + \text{Cdk}$$

Question 1

Which of the following best describes the function of the protein p53 in the cell cycle?

Accepted Answer

It acts as a tumor suppressor by pausing the cell cycle to allow DNA repair or triggering apoptosis if damage is irreparable.

Question 2

A cell is observed to have high levels of cyclin, high levels of Cdk, but low MPF activity. Which phase of the cell cycle is this cell most likely in?

Accepted Answer

Early G2 phase

Question 3

What is the primary molecular mechanism by which MPF (M-phase promoting factor) is activated at the end of G2 phase?

Accepted Answer

Removal of an inhibitory phosphate group from the Cdk subunit

Question 4

Which of the following equations correctly represents the composition of MPF?

Accepted Answer

$$	ext{MPF} = 	ext{Cyclin} + 	ext{Cdk}$$

Question 5

A mutation causes the Rb protein to be nonfunctional. What is the most likely consequence for the cell?

Accepted Answer

E2F will be continuously active, leading to uncontrolled entry into S phase.

Question 6

Which checkpoint is primarily responsible for ensuring that all chromosomes are properly attached to the spindle before anaphase begins?

Accepted Answer

M-phase (spindle assembly) checkpoint

Question 7

If a cell has a defective p53 gene, what is the most likely outcome after DNA damage occurs?

Accepted Answer

The cell will continue to divide, accumulating mutations.

Question 8

Which of the following best explains why cancer cells can divide uncontrollably?

Accepted Answer

They have mutations that either activate proteins promoting division or inactivate tumor suppressor proteins.

Question 9

A researcher observes a tumor that does not invade nearby tissues and does not spread to other parts of the body. This tumor is best classified as:

Accepted Answer

Benign

Question 10

Which of the following is a direct result of MPF activity during mitosis?

Accepted Answer

Phosphorylation of proteins that initiate chromosome condensation and spindle formation

Question 11

What is the role of ubiquitin-mediated proteolysis in the regulation of the cell cycle?

Accepted Answer

It targets cyclin for destruction, thereby inactivating MPF and allowing exit from mitosis.

Question 12

Which of the following best describes the difference between benign and malignant tumors?

Accepted Answer

Benign tumors do not invade nearby tissues, while malignant tumors are invasive and can metastasize.

Question 13

A cell is exposed to a growth factor that stimulates passage through the G1 checkpoint. Which molecular event is most likely to occur?

Accepted Answer

Activation of G1 cyclin-Cdk complex, leading to phosphorylation of Rb and release of E2F.

Question 14

Which of the following scenarios would most likely lead to the development of cancer?

Accepted Answer

A mutation that causes overproduction of G1 cyclin, resulting in continuous activation of Cdk.

Question 15

Which of the following best represents the sequence of phases in the eukaryotic cell cycle?

Accepted Answer

$$G_1$$ \rightarrow S \rightarrow $$G_2$$ \rightarrow M$$

Question 16

A patient is diagnosed with a cancer in which half of the tumor cells have a defective p53 gene. What is the most significant risk associated with this mutation?

Accepted Answer

Accumulation of additional mutations due to failure to repair DNA damage.

Question 17

Which of the following is an example of negative feedback in the regulation of the cell cycle?

Accepted Answer

Destruction of cyclin after mitosis, leading to inactivation of MPF.

Question 18

Which of the following statements about the G0 phase is correct?

Accepted Answer

Cells in G0 have exited the cell cycle and do not actively divide.

Question 19

A scientist discovers a new drug that prevents the removal of the inhibitory phosphate from Cdk. What effect would this drug have on the cell cycle?

Accepted Answer

Cells would be unable to activate MPF and would not enter mitosis.

ch 12 pt 2

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