Question 1

Which phase of the cell cycle is primarily responsible for DNA replication, and what ensures that replication occurs only once per cycle?

Accepted Answer

S phase; S-Cdk phosphorylates Cdc6 to block re-replication

Question 2

A cell is exposed to X-rays, resulting in DNA damage during G1. Which molecular pathway is activated to halt cell cycle progression?

Accepted Answer

Activation of p53, upregulation of p21, inhibition of G1/S-Cdk

Question 3

Which of the following best describes the role of mitogens in cell cycle regulation?

Accepted Answer

Mitogens stimulate production of G1-Cdk and G1/S-Cdk complexes

Question 4

What would likely happen in a mammalian cell with a loss-of-function mutation in p53?

Accepted Answer

Cells would fail to halt the cell cycle in response to DNA damage, increasing cancer risk

Question 5

During which stage of mitosis does the nuclear envelope break down, allowing chromosomes to attach to the mitotic spindle?

Accepted Answer

Prometaphase

Question 6

Which protein complex is responsible for marking cyclins for degradation, and what is the consequence of this process?

Accepted Answer

APC/C; allows cell to exit M phase and enter G1

Question 7

A scientist injects cytoplasm from an M-phase cell into an interphase oocyte. What is the expected outcome and what does this experiment demonstrate?

Accepted Answer

Oocyte enters M phase; demonstrates presence of M-phase promoting factor (MPF)

Question 8

Which checkpoint ensures that all chromosomes are properly attached to the mitotic spindle before proceeding to anaphase?

Accepted Answer

Spindle assembly checkpoint

Question 9

What is the function of the protein p27 in cell cycle regulation?

Accepted Answer

p27 inhibits cyclin-Cdk complexes, preventing cell cycle progression

Question 10

Which equation best represents the relationship between cell cycle duration ($$T$$), number of cell divisions ($$n$$), and total elapsed time ($$t$$)?

Accepted Answer

$$t = n 	imes T$$

Question 11

Which molecular event triggers the separation of sister chromatids during anaphase?

Accepted Answer

APC/C-mediated degradation of securin, activating separase

Question 12

If a cell is depleted of nucleotides during S phase, what is the most likely outcome?

Accepted Answer

Cell will arrest at the G2/M checkpoint due to incomplete DNA replication

Question 13

Which of the following statements about cyclin-dependent kinases (Cdks) is correct?

Accepted Answer

Cdks are only active when bound to their specific cyclins

Question 14

What is the primary function of the contractile ring during cytokinesis?

Accepted Answer

Pinch the cell into two daughter cells using actin and myosin filaments

Question 15

Which signaling pathway is most directly involved in stimulating cell growth and preventing apoptosis?

Accepted Answer

RTK-AKT-Tor pathway

Question 16

A cell with a mutation that causes constant expression of p21 would most likely:

Accepted Answer

Arrest in G1 phase and fail to enter S phase

Question 17

Which of the following is NOT a function of the G2/M checkpoint?

Accepted Answer

Ensuring all chromosomes are attached to the spindle

Question 18

Which protein is responsible for inhibiting the activity of M-Cdk until conditions are favorable for mitosis?

Accepted Answer

Wee1 kinase

Question 19

What is the role of cohesins and condensins during mitosis?

Accepted Answer

Cohesins tie together sister chromatids; condensins help condense chromosomes

Question 20

Which equation describes the exponential increase in cell number ($$N) $$after $$n$$ cell divisions, starting from a single cell?

Accepted Answer

$$N = 2^n$$

The Cell Cycle: Regulation, Phases, and Control Mechanisms

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