$$\text{Cdk activity} \propto \text{Cyclin concentration}$$

Question 1

Which of the following best describes the role of histone H1 in DNA packaging within the nucleus?

Accepted Answer

Histone H1 binds to the linker DNA region between nucleosomes, helping to stabilize higher-order chromatin structure.

Question 2

During which phase of mitosis does the nuclear envelope break down, allowing microtubules to interact with chromosomes?

Accepted Answer

Prometaphase

Question 3

What is the primary function of the kinetochore during mitosis?

Accepted Answer

To attach chromosomes to spindle microtubules and facilitate their movement during cell division

Question 4

Which equation best represents the relationship between cyclin-dependent kinase (Cdk) activity and cyclin concentration during the cell cycle?

Accepted Answer

$$	ext{Cdk activity} \propto 	ext{Cyclin concentration}$$

Question 5

A cell is arrested at the G2-M transition. Which of the following is most likely responsible for this arrest?

Accepted Answer

Incomplete DNA replication or DNA damage

Question 6

Which protein complex is responsible for targeting Securin for degradation, thereby allowing sister chromatid separation?

Accepted Answer

Anaphase-Promoting Complex (APC)

Question 7

What is the effect of Taxol on mitosis, and which process does it inhibit?

Accepted Answer

Taxol inhibits microtubule depolymerization, preventing chromosome movement toward the poles.

Question 8

Which of the following steps is required to activate the mitotic Cdk-cyclin complex?

Accepted Answer

Binding of cyclin to Cdk and removal of inhibitory phosphates by a phosphatase

Question 9

A mutation in the destruction box of cyclin B prevents its degradation. What is the most likely consequence for the cell cycle?

Accepted Answer

The cell will be unable to transition from M phase to G1, blocking cytokinesis.

Question 10

Which checkpoint is primarily responsible for preventing cells with damaged DNA from entering S phase?

Accepted Answer

G1/S checkpoint

Question 11

What is the role of p53 in cell cycle regulation?

Accepted Answer

p53 stimulates expression of p21, which inhibits cyclin-Cdks and arrests the cell cycle in response to DNA damage.

Question 12

Which of the following best explains why retinoblastoma (Rb) is considered a tumor suppressor?

Accepted Answer

Rb inhibits the G1-S transition by sequestering E2F, preventing uncontrolled cell division.

Question 13

Which molecular event triggers the release of E2F from Rb, allowing progression into S phase?

Accepted Answer

Phosphorylation of Rb by Cyclin D-Cdk4/6

Question 14

Which of the following is a direct consequence of a loss-of-function mutation in p53?

Accepted Answer

Cells replicate damaged DNA, increasing the risk of cancerous transformation.

Question 15

Which equation describes the effect of phosphorylation on the activity of a Cdk-cyclin complex?

Accepted Answer

$$	ext{Cdk-cyclin activity} = 	ext{Inactive unless activating phosphate is present and inhibitory phosphates are removed}$$

Question 16

Which of the following best describes the function of the contractile ring during cytokinesis in animal cells?

Accepted Answer

It is composed of actin and myosin II filaments, producing a contractile force that cleaves the cell into two.

Question 17

Which process is directly inhibited by MPF phosphorylation of myosin II during mitosis?

Accepted Answer

Cleavage furrow formation and cytokinesis

Question 18

Which molecular pathway is activated by growth factors to promote cell cycle progression through the G1 restriction point?

Accepted Answer

RTK-Ras-MAPK pathway

Question 19

Which of the following is a plausible outcome if the spindle assembly checkpoint fails during mitosis?

Accepted Answer

Chromosomes may not be properly attached to the spindle, leading to aneuploidy.

The Eukaryotic Cell Cycle, Mitosis, and Cell Cycle Regulation

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