Ch. 12

If a cell at metaphase of mitosis contains 20 sister chromatids, how many chromosomes will be present in a G1 cell?

10

In a diploid cell with 5 chromosome pairs (2n = 10), how many centromeres will be found in a nucleus at G2 of the cell division cycle?

10

A group of cells is assayed for DNA content immediately following mitosis and is found to have an average of 8 picograms of DNA per nucleus. How many picograms of DNA would be found in a nucleus at prophase of mitosis?

16

If there are 40 centromeres in a cell at anaphase of mitosis, how many chromosomes will be found in each daughter cell following cytokinesis?

20

Starting with a fertilized egg (zygote), a series of six cell divisions would produce an early embryo with how many cells?

64

Which of the following properties is associated with a cyclin-dependent kinase (Cdk)?

A Cdk is an enzyme that attaches phosphate groups to other proteins.

A cleavage furrow is

A groove in the plasma membrane between daughter nuclei

Motor proteins require which of the following to function in the movement of chromosomes toward the poles of the mitotic spindle?

ATP as an energy source

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

As cells become more numerous, the cell surface proteins of one cell contact the adjoining cells, and they signal each other to stop dividing.

The unlettered circle at the top of the figure shows a diploid nucleus with four chromosomes that have not yet replicated. There are two pairs of homologous chromosomes, one long and the other short. One haploid set is black, and the other is gray. The circles labeled A to E show various combinations of these chromosomes. What is the correct chromosomal condition at prometaphase of mitosis?

B

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

Cdk

Cells from advanced malignant tumors often have very abnormal chromosomes and an abnormal number of chromosomes. What might explain the association between malignant tumors and chromosomal abnormalities?

Cell cycle checkpoints are not in place to stop cells with chromosome abnormalities.

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

Cyclin

What is the correct chromosomal condition for one daughter nucleus at telophase of mitosis?

D (incorrect)

The data in the table were obtained from a study of the length of time spent in each phase of the cell cycle by cells of three eukaryotic organisms designated beta, delta, and gamma. What is the best explanation for the data associated with delta cells?

Delta cells are in the G0 phase.

Measurements of the amount of DNA per nucleus were taken on a large number of cells from a growing fungus. The measured DNA levels ranged from 3 to 6 picograms per nucleus. In which stage of the cell cycle did the nucleus contain 6 picograms of DNA?

G2

In the figure, G1 is represented by which numbered part(s) of the cycle?

I or V

In the figure, which number represents DNA synthesis?

II

In the figure, MPF reaches its highest concentration during this stage.

III

In the figure, at which of the numbered regions would you expect to find cells at metaphase?

III only

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

PDGF

How is plant cell cytokinesis different from animal cell cytokinesis?

Plant cells deposit vesicles containing cell-wall building blocks on the metaphase plate; animal cells form a cleavage furrow.

Early observations of a cultured cell line indicated that the cells did not exhibit either density-dependent inhibition or anchorage dependence. What do these observations suggest about this cell line?

The cells show characteristics of tumors.

What would you expect to happen if MPF (maturation-promoting factor) is introduced into immature frog oocytes that are arrested in G2?

The cells would enter mitosis.

Once a cell enters mitosis, the molecules that activate division must be turned off. What happens to MPF during mitosis?

The cyclin component of MPF is degraded.

In what way do kinetochore microtubules facilitate the process of splitting the centromeres?

They create tension by pulling toward opposite poles.

Why do neurons and some other specialized cells divide infrequently?

They have entered into G0.

Several organisms, primarily protists, have what are called intermediate mitotic organization. What is the most probable hypothesis about these intermediate forms of cell division?

They show some but not all of the evolutionary steps toward complete mitosis.

Through a microscope, you can see a cell plate beginning to develop across the middle of a cell and nuclei forming on either side of the cell plate. This cell is most likely

a plant cell in the process of cytokinesis.

During which phase of mitosis do the chromatids become chromosomes?

anaphase

The drug cytochalasin B blocks the function of actin. Which of the following aspects of the animal cell cycle would be most disrupted by cytochalasin B?

cleavage furrow formation and cytokinesis

What two components constitute an active MPF?

cyclin and a cyclin-dependent kinase

If the cell whose nuclear material is shown in Figure 12.2 continues toward completion of mitosis, which of the following events would occur next? A) cell membrane synthesis B) spindle fiber formation C) nuclear envelope breakdown D) formation of telophase nuclei E) synthesis of chromatids

formation of telophase nuclei

Scientists isolate cells in various phases of the cell cycle. They find a group of cells that have 1.5 times more DNA than G1 phase cells. The cells of this group are _____.

in the S phase of the cell cycle

Nucleotides can be radiolabeled before they are incorporated into newly forming DNA and can therefore be assayed to track their incorporation. In a set of experiments, a student-faculty research team used labeled T nucleotides and introduced these into the culture of dividing human cells at specific times. The research team used the setup to study the incorporation of labeled nucleotides into a culture of lymphocytes and found that the lymphocytes incorporated the labeled nucleotide at a significantly higher level after a pathogen was introduced into the culture. They concluded that

infection causes lymphocytes to divide more rapidly

Besides the ability of some cancer cells to overproliferate, what else could logically result in a tumor?

lack of appropriate cell death

At what stage of the cell cycle is the cyclin component of MPF destroyed?

late (m)

The M phase checkpoint ensures that all chromosomes are attached to the mitotic spindle. If this does not happen, cells would most likely be arrested in

metaphase

Taxol is an anticancer drug extracted from the Pacific yew tree. In animal cells, Taxol disrupts microtubule formation by binding to microtubules and accelerating their assembly from the protein precursor, tubulin. Surprisingly, this stops mitosis. Specifically, Taxol must affect

mitotic spindle formation

At which phase of the cell cycle do centrioles begin to move apart in animal cells?

prophase

Which of the following events occurs during interphase of the cell cycle?

replication of DNA

The mitotic spindle plays a critical role in which of the following processes

separation of sister chromatids

Movement of the chromosomes during anaphase would be most affected by a drug that prevents

shortening of microtubules

In the cells of many eukaryotic species, the nuclear envelope has to disappear to permit which of the following events in the cell cycle?

the attachment of microtubules to kinetochores

FtsZ is a bacterial cytoskeletal protein that forms a contractile ring involved in bacterial cytokinesis. Its function is analogous to _____.

the cleavage furrow of eukaryotic animal cells