Question 1

Which of the following triggers the cell's passage past the G₂ checkpoint into mitosis?

Accepted Answer

The cell's passage past the G₂ checkpoint into mitosis is triggered by MPF (Mitosis-promoting factor), which is a complex of cyclin and Cdk (cyclin-dependent kinase). Cyclin levels increase during G₂ phase, forming a complex with Cdk, and activating it to form MPF. MPF triggers the cell's entry into mitosis. Therefore, option B is the best choice.

Question 2

Which of the following describe(s)cyclin-dependent kinase (Cdk)?

Accepted Answer

The answer of Which of the following describe(s)cyclin-dependent kinase (Cdk)?
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Question 3

A plant-derived protein known as colchicine can be used to poison cells by blocking the formation of the spindle. Which of the following would result if colchicine is added to a sample of cells in G₂?

Accepted Answer

In G₂ phase, the chromosomes have already duplicated and are coiled and condensed in preparation for mitosis. If colchicine is added, the formation of the spindle is blocked, and the chromosomes cannot attach to it. Therefore, the chromosomes would coil and shorten but have no spindle to which to attach. The cells would be unable to progress through mitosis and divide, resulting in cell death.

Question 4

Proteins that are involved in the regulation of the cell cycle, and that show fluctuations in concentration during the cell cycle, are called

Accepted Answer

Proteins that regulate the cell cycle and fluctuate in concentration are called cyclins. Kinetochores are protein structures on chromosomes involved in cell division, kinases are enzymes that regulate various cellular processes including the cell cycle, ATPases are enzymes that hydrolyze ATP for cellular energy, and proton pumps are membrane proteins that transport protons across cell membranes.

Question 5

Which of the following proteins are involved in binary fission as well as eukaryotic mitotic division?

Accepted Answer

Actin and tubulin are involved in both binary fission in prokaryotes and mitotic division in eukaryotes. Cyclins, Cdks, and MPF are specific to eukaryotic cell division, while cohesins are involved in chromosome structure and separation during mitosis, but not binary fission.

Question 6

Which of the following is released by platelets in the vicinity of an injury?

Accepted Answer

Platelet-derived growth factor (PDGF) is released by platelets in the vicinity of an injury.

Question 7

Which of the following is true concerning cancer cells?

Accepted Answer

Cancer cells do not exhibit density-dependent inhibition, meaning they can continue to grow and divide even when there is no space for them to do so. They also do not follow normal cell cycle controls, leading to uncontrolled cell division. Additionally, when they do stop dividing, it is at random points in the cell cycle, rather than following the orderly progression seen in normal cells.

Question 8

Which of the following is a protein maintained at constant levels throughout the cell cycle that requires cyclin to become catalytically active?

Accepted Answer

Cdk (cyclin-dependent kinases) are proteins that are maintained at constant levels throughout the cell cycle and require binding to cyclins to become catalytically active.

Question 9

Using which of the following techniques would enable your lab group to distinguish between a cell in G₂ and a cell from the same organism in G₁?

Accepted Answer

Radioactive-labeled nucleotides can be used to measure DNA synthesis. Cells in G₂ have completed DNA replication and have twice the DNA content compared to cells in G₁, which have not yet replicated their DNA.

Question 10

Which of the following is (are)required for motor proteins to function in the movement of chromosomes toward the poles of the mitotic spindle?

Accepted Answer

Motor proteins require ATP as an energy source to facilitate the movement of chromosomes along the mitotic spindle.

Question 11

Which of the following was a discovery that had to be made before human chromosomes could be correctly counted?

Accepted Answer

Using a hypotonic solution to swell nuclei was crucial because it allowed chromosomes to spread out and be more easily counted under a microscope.

Question 12

Density-dependent inhibition is explained by which of the following?

Accepted Answer

Density-dependent inhibition occurs when the cell surface proteins of one cell contact the adjoining cells and they stop dividing, thereby regulating cell population density. This mechanism helps maintain tissue homeostasis and prevent uncontrolled cell proliferation. Option A is incorrect as it describes cell contact inhibition. Option C is incorrect as it is not a recognized mechanism for density-dependent inhibition. Option D is incorrect as it suggests an incorrect relationship between cell density and the cell cycle. Option E is incorrect as waste product accumulation is not a factor in density-dependent inhibition.

Question 13

Which of the following is a protein synthesized at specific times during the cell cycle that associates with a kinase to form a catalytically active complex?

Accepted Answer

Cyclin is synthesized at specific times during the cell cycle and associates with a kinase (Cdk) to form a catalytically active complex, which is crucial for cell cycle progression.

Question 14

A mutation results in a cell that no longer produces a normal protein kinase for the M phase checkpoint. Which of the following would likely be the immediate result of this mutation?

Accepted Answer

The answer of A mutation results in a cell that...

Question 15

What is a cleavage furrow?

Accepted Answer

A cleavage furrow is a groove in the plasma membrane between daughter nuclei during cell division. It is formed by the contraction of actin filaments that pull the membrane inward, eventually separating the two daughter cells. A cleavage furrow is specific to animal cells and is different from the cell plate that forms during cytokinesis in plant cells.

Question 16

A particular cyclin called cyclin E forms a complex with Cdk 2 (cyclin-dependent kinase 2). This complex is important for the progression of the cell from G₁ into the S phase of the cell cycle. Which of the following statements is correct?

Accepted Answer

The cyclin E/Cdk 2 complex is most important for the progression from G₁ to S phase, therefore it follows that the amount of free cyclin E (not bound to Cdk 2) will be highest during G₁ when the cell is making preparations to enter the S phase. Similarly, the amount of free Cdk 2 will be greater during the G₁ phase as it is available to bind with cyclin E to form the active complex. Therefore, options A, B, and D are incorrect. Option E is also incorrect as the cyclin E/Cdk 2 complex is most active during the G₁/S transition, not during G₂.

Question 17

What causes the decrease in the amount of cyclin at a specific point in the cell cycle?

Accepted Answer

Cyclin is degraded by proteolysis once its complex with Cdk has completed its work in the cell cycle, leading to a decrease in the amount of cyclin at a specific point in the cycle. This is necessary to prevent cells from continually dividing and to prepare them for the next phase of the cycle.

Question 18

The cyclin component of MPF is destroyed toward the end of which phase?

Accepted Answer

The cyclin component of MPF is destroyed toward the end of the M phase, specifically during the process of cytokinesis. This is what triggers the exit from mitosis and entrance into interphase. Therefore, the correct option is E, M.

Question 19

The MPF protein complex turns itself off by

Accepted Answer

The MPF protein complex turns itself off by activating a process that destroys cyclin components. This degradation of cyclin results in the inactivation of the MPF complex, which prevents the phosphorylation of its target proteins and allows the cell to progress to the next stage of the cell cycle.

Question 20

You have the technology necessary to measure each of the following in a sample of animal cells: chlorophylls, organelle density, picograms of DNA, cell wall components, and enzymatic activity. Which would you expect to increase significantly from M to G₁?

Accepted Answer

During the G₁ phase of the cell cycle, cells are focused on growth and preparation for DNA replication in S phase. This means that the organelle density would increase as the cell grows and prepares for cell division, and enzymatic activity would also increase as the cell prepares to replicate its DNA. Cell wall components, picograms of DNA, and chlorophylls would not necessarily see a significant increase during this phase.

Quiz 12: The Cell Cycle