Q: Which of the following equations correctly represents the process by which a protein kinase transfers a phosphate group from ATP to a substrate?

$$ \mathrm{ATP} + \text{substrate} \rightarrow \mathrm{ADP} + \text{phosphorylated substrate} $$

Question 1

Which of the following best describes the function of the M phase-promoting factor (MPF) in the cell cycle?

Accepted Answer

MPF is a cyclin-Cdk complex that triggers the cell's entry into mitosis by phosphorylating target proteins.

Question 2

A cell is observed to have high levels of cyclin, high levels of Cdk, but low MPF activity. Which of the following best explains this observation?

Accepted Answer

The Cdk is phosphorylated at an inhibitory site, preventing MPF activation despite high cyclin levels.

Question 3

Which of the following equations correctly represents the process by which a protein kinase transfers a phosphate group from ATP to a substrate?

Accepted Answer

$$ \mathrm{ATP} + 	ext{substrate} ightarrow \mathrm{ADP} + 	ext{phosphorylated substrate} $$

Question 4

A mutation causes the cyclin subunit of MPF to be non-degradable. What is the most likely consequence for the cell?

Accepted Answer

The cell will have constitutively active MPF, leading to uncontrolled mitosis.

Question 5

Which checkpoint is primarily responsible for ensuring that DNA damage is repaired before the cell enters S phase, and what protein is central to this process?

Accepted Answer

G1 checkpoint; p53

Question 6

A patient is diagnosed with a tumor in which the Rb protein is defective and cannot bind E2F. What is the most likely effect on the cell cycle?

Accepted Answer

Cells will enter S phase uncontrollably, leading to excessive cell division.

Question 7

Which of the following best describes the role of p53 in the cell cycle?

Accepted Answer

p53 is a tumor suppressor that can pause the cell cycle or initiate apoptosis in response to DNA damage.

Question 8

Which of the following scenarios would most likely result in a benign tumor rather than a malignant tumor?

Accepted Answer

Cells divide uncontrollably but do not invade surrounding tissues or spread to other sites.

Question 9

If a cell is exposed to a growth factor that specifically increases the production of G1 cyclin, what is the most likely outcome?

Accepted Answer

The cell will be more likely to pass the G1 checkpoint and enter S phase.

Question 10

Which of the following best explains why neurons and muscle cells are typically found in the G0 phase?

Accepted Answer

They have exited the cell cycle and are in a non-dividing, arrested state.

Question 11

A researcher observes that a certain cell type has a very short G1 phase and divides rapidly. Which of the following is the most likely explanation?

Accepted Answer

The cell type is likely in early development, where rapid division is necessary.

Question 12

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

Accepted Answer

MPF activity leads to the destruction of cyclin, which in turn inactivates MPF.

Question 13

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

Accepted Answer

Benign tumors are noncancerous and noninvasive, while malignant tumors are cancerous and can invade other tissues.

Question 14

A cell with a defective p53 gene is exposed to UV radiation, causing DNA damage. What is the most likely outcome?

Accepted Answer

The cell will continue to divide, accumulating mutations that may lead to cancer.

Question 15

Which of the following best explains why most cancer-causing mutations arise in somatic cells rather than being inherited?

Accepted Answer

Somatic cells are exposed to environmental factors that can cause mutations during an individual's lifetime.

Question 16

Which of the following is a direct result of overproduction of G1 cyclin in a cell?

Accepted Answer

Permanent activation of Cdk, leading to continuous phosphorylation of Rb and uncontrolled entry into S phase.

Question 17

Which of the following best describes the role of checkpoints in the cell cycle?

Accepted Answer

Checkpoints are critical control points where regulatory molecules determine whether the cell proceeds to the next stage.

Question 18

A cell is found to have a mutation that prevents the removal of the inhibitory phosphate from Cdk. What is the most likely effect on the cell cycle?

Accepted Answer

The cell will be unable to activate MPF and will not enter mitosis.

Question 19

Which of the following best explains why cancer cells can invade nearby tissues and spread to other sites in the body?

Accepted Answer

They have lost normal cell-cycle control, allowing them to divide uncontrollably and metastasize.

Regulation of the Cell Cycle and Cancer

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