Question 1

Which phase of the cell cycle is characterized by DNA synthesis, and what is the main event occurring during this phase?

Accepted Answer

S phase; replication of DNA

Question 2

A neuron is considered to be in a non-dividing, arrested state. Which phase of the cell cycle is it most likely in?

Accepted Answer

G0 phase

Question 3

What is the role of cyclin-dependent kinase (Cdk) in the MPF complex?

Accepted Answer

It catalyzes the transfer of a phosphate group from ATP onto a substrate.

Question 4

During which stage of the cell cycle would you expect cyclin levels to be highest?

Accepted Answer

Late G2 phase

Question 5

Which of the following best describes the negative feedback mechanism that turns off MPF activity?

Accepted Answer

An enzyme tags cyclin for destruction, leading to its degradation.

Question 6

A cell with defective p53 protein is likely to:

Accepted Answer

Accumulate mutations due to lack of cell cycle arrest

Question 7

Which checkpoint is primarily responsible for ensuring that the cell does not proceed to S phase with damaged DNA?

Accepted Answer

G1 checkpoint

Question 8

If a mutation causes overproduction of G1 cyclin, what is the most likely consequence for the cell?

Accepted Answer

Permanent activation of Cdk and uncontrolled entry into S phase

Question 9

Which of the following equations correctly represents the total duration of interphase in the cell cycle?

Accepted Answer

$$Interphase = G_1$ + S + G_2$

Question 10

A malignant tumor differs from a benign tumor in that malignant cells:

Accepted Answer

Can invade nearby tissues and spread to other sites (metastasis)

Question 11

Which protein acts as a 'brake' on the cell cycle and is commonly mutated in half of all cancers?

Accepted Answer

p53

Question 12

What is the function of the retinoblastoma protein (Rb) in the G1 checkpoint?

Accepted Answer

Rb binds to E2F and prevents activation of S phase genes

Question 13

Which Nobel Prize-winning discovery led to the identification of the M phase-promoting factor (MPF)?

Accepted Answer

Discovery of regulatory molecules that induce mitosis

Question 14

A cell is observed to have high levels of cyclin, active Cdk, and is undergoing chromosome condensation. Which phase is it most likely in?

Accepted Answer

M phase (mitosis)

Question 15

Which of the following scenarios best illustrates the concept of negative feedback in cell cycle regulation?

Accepted Answer

MPF activity leads to cyclin degradation, which in turn decreases MPF activity

Question 16

If a cell has a defective Rb protein, what is the most likely outcome?

Accepted Answer

E2F is continuously active, leading to uncontrolled entry into S phase

Question 17

Which of the following is NOT a property of cancer cells?

Accepted Answer

Permanent cell cycle arrest in G0

Question 18

Which equation best represents the phosphorylation reaction catalyzed by protein kinase in the MPF complex?

Accepted Answer

$$ATP + Protein \rightarrow ADP + Protein{-}P$$

Question 19

Which of the following is a direct consequence of checkpoint failure in the cell cycle?

Accepted Answer

Cells divide uncontrollably, leading to cancer

Question 20

A researcher observes that a cell line has continuously phosphorylated Rb and high E2F activity. What is the most likely explanation?

Accepted Answer

G1 cyclin is overproduced, leading to permanent Cdk activation

Regulation of the Cell Cycle and Cancer

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