Question 1

Which phase of the eukaryotic cell cycle is primarily responsible for DNA replication?

Accepted Answer

S phase

Question 2

A researcher uses a flow cytometer to analyze DNA content in a population of cells. Which peak corresponds to cells in the G2 and M phases?

Accepted Answer

Peak at 2 relative DNA content

Question 3

Which of the following best describes the role of cyclin-dependent kinases (Cdks) in the cell cycle?

Accepted Answer

Cdks phosphorylate target proteins to regulate cell cycle transitions

Question 4

What is the function of the protein Wee1 kinase in cell cycle regulation?

Accepted Answer

It adds inhibitory phosphates to Cdks, suppressing their activity

Question 5

During which cell cycle checkpoint does the cell verify that all chromosomes are properly attached to the spindle before proceeding?

Accepted Answer

Metaphase-to-anaphase transition

Question 6

A mutation causes the loss of function of Cdc25 phosphatase. What is the most likely consequence for the cell cycle?

Accepted Answer

Cdks remain inactive due to persistent inhibitory phosphorylation

Question 7

Which cyclin-Cdk complex is responsible for triggering entry into mitosis in vertebrate cells?

Accepted Answer

M-Cdk (Cyclin B/Cdk1)

Question 8

If a cell experiences DNA damage during G1 phase, which regulatory protein is most likely to be activated to halt cell cycle progression?

Accepted Answer

p21

Question 9

Which of the following best explains why cyclin levels fluctuate during the cell cycle?

Accepted Answer

Cyclins are degraded and synthesized at specific cell cycle stages to regulate Cdk activity

Question 10

A cell is observed to have twice the normal DNA content but has not yet divided. Which phase is it most likely in?

Accepted Answer

G2 phase

Question 11

Which protein complex is responsible for catalyzing the ubiquitination and degradation of cyclins at the end of mitosis?

Accepted Answer

APC/C (Anaphase-Promoting Complex/Cyclosome)

Question 12

What is the main consequence of p27 binding to a cyclin-Cdk complex?

Accepted Answer

Inhibition of Cdk activity

Question 13

Which equation best represents the relationship between DNA content and cell cycle phase as measured by flow cytometry?

Accepted Answer

$$DNA_{G1} = DNA_{G2}/2$$

Question 14

A cell is exposed to a drug that inhibits the activity of Cdk-activating kinase (CAK). What is the expected effect on the cell cycle?

Accepted Answer

Cdks remain inactive due to lack of activating phosphorylation

Question 15

Which of the following events is directly triggered by the activation of M-Cdk?

Accepted Answer

Entry into mitosis (nuclear division)

Question 16

In a cell with defective APC/C, which process would be most directly affected?

Accepted Answer

Degradation of M-cyclin and exit from mitosis

Question 17

Which checkpoint ensures that the environment is favorable before the cell commits to DNA replication?

Accepted Answer

G1/S checkpoint

Question 18

A cell is stained to visualize S-phase cells. What is being detected in these cells?

Accepted Answer

DNA replication

Question 19

Which of the following is a multi-step process that involves both cyclin synthesis and Cdk activation to drive the cell from G1 to S phase?

Accepted Answer

Degradation of p27 and phosphorylation of Rb protein

Question 20

Which regulatory protein acts as a biochemical switch to prevent DNA re-replication within a single cell cycle?

Accepted Answer

S-Cdk

Eukaryotic Cell Cycle: Phases, Regulation, and Control Systems

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