The Cell Cycle

Study the data in the histograms. (a) Which axis indirectly shows the relative amount of DNA per cell? Explain your answer. (b) In the control sample, compare the first peak in the histogram (in region A) to the second peak (in region C). Which peak shows the population of cells with the higher amount of DNA per cell? Explain. (For additional information about graphs, see the Scientific Skills Review in Appendix F.)

In Figure 12.14, why do the nuclei resulting from experiment 2 contain different amounts of DNA?

(a) an animal cell in the process of cytokinesis.

(b) a plant cell in the process of cytokinesis.

(c) a bacterial cell dividing

(d) a plant cell in metaphase

(a) In the control sample histogram, identify the phase of the cell cycle (G1, S, or G2) of the population of cells in each region delineated by vertical lines. Label the histogram with these phases and explain your answer. (b) Does the S phase population of cells show a distinct peak in the histogram? Why or why not?

How does MPF allow a cell to pass the G₂ phase checkpoint and enter mitosis?(See Figure 12.16)

Vinblastine is a standard chemotherapeutic drug used to treat cancer. Because it interferes with the assembly of microtubules, its effectiveness must be related to

(A) disruption of mitotic spindle formation.

(B) suppression of cyclin production

(C) myosin denaturation and inhibition of cleavage furrow formation 

(D) inhibition of DNA synthesis

The histogram representing the treated sample shows the effect of growing the cancer cells alongside human umbilical cord stem cells that produce the potential inhibitor. (a) Label the histogram with the cell cycle phases. Which phase of the cell cycle has the greatest number of cells in the treated sample? Explain. (b) Compare the distribution of cells among G1, S, and G2 phases in the control and treated samples. What does this tell you about the cells in the treated sample? (c) Based on what you learned in Concept 12.3, propose a mechanism by which the stem cell-derived inhibitor might arrest the cancer cell cycle at this stage. (More than one answer is possible.)

Explain how receptor tyrosine kinases and intracellular receptors might function in triggering cell division. (Review Figures 11.8 and 11.9 and concept 11.2)

One difference between cancer cells and normal cells is that cancer cells

(A) are unable to synthesize DNA.

(B) are arrested at the S phase of the cell cycle.

(C) continue to divide even when they are tightly packed together.

(D) cannot function properly because they are affected by density-dependent inhibition.

The decline of MPF activity at the end of mitosis is due to 

(A)  the destruction of the protein kinase CDK.

(B) decreased synthesis of Cdk.

(C) degradation of cyclin

(D) accumulation of cyclin.

In the cells of some organisms, mitosis occurs without cytokinesis. This will result in 

(A)  cells with more than one nucleus.

(B) cells that are unusually small.

(C) cells lacking nuclei.

(D) cell cycles lacking an S phase

Which of the following does not occur during mitosis?

(A) Condensation of the chromosomes.

(B) Replication of DNA.

(C) Separation of sister chromatids.

(D) Spindle formation

Cell A has as much DNA as cells B, C, and D in mitotically active tissue. Cell A is most likely in

(A) G₁.

(B) G₂

(C) prophase.

(D) metaphase

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?

(A) Spindle formation

(B) Spindle attachment to kinetochores

(C) Cell elongation during anaphase

(D) Cleavage furrow formation and cytokinesis

The light micrograph shows dividing cells near the tip of an onion root. Identify a cell in each of the following stages: prophase, prometaphase, metaphase, anaphase, and telophase. Describe the major events occurring at each stage.

Draw one eukaryotic chromosome as it would appear during interphase, during each of the stages of mitosis, and during cytokinesis. Also, draw and label the nuclear envelope and any microtubules attached to the chromosome(s).

The result of mitosis is that the daughter cells end up with the same number of chromosomes that the parent cell had. Another potential way to maintain the number of chromosomes would be to carry out cell division first and then duplicate the chromosomes in each daughter cell. Assess whether this would be an equally good way of organizing the cell cycle. Explain why evolution had not led to this alternative.

Although both ends of a microtubule can gain or lose subunits, one end (called the plus end) polymerizes and depolymerizes at a higher rate than the other end (the minus end). For spindle microtubules, the plus ends are in the center of the spindle, and the minus ends are at the poles. Motor proteins that move along microtubules specialize in walking either toward the plus end-directed and minus end-directed motor proteins, respectively. Given what you know about chromosome movement and spindle changes during anaphase, predict which type of motor proteins would be present on (a) kinetochore microtubules and (b) non-kinetochore microtubules.

The continuity of life is based on heritable information in the form of DNA. In a short essay (100-150 words), explain how the process of mitosis faithfully parcels out exact copies of this heritable information in the production of genetically identical daughter cells.

Shown here are two HeLa cancer cells that are just completing cytokinesis. Explain how the cell division of cancer cells like these is misregulated. Identify genetic and other changes that might have caused these cells to escape normal cell cycle regulation.

How many chromosomes are drawn in each part of figure 12.5? (Ignore the micrograph in step2.)

A chicken has 78 chromosomes in its somatic cells. How many chromosomes did the chicken inherit from each parent? How many chromosomes are in each of the chicken’s gamete? How many chromosomes will be in each somatic cell of the chicken’s offspring?

How many chromosomes are shown in the illustration in Figure 12.8? Are they duplicated? How many chromatids are shown?

Compare cytokinesis in animal cells and plant cells.

During which stages of the cell cycle does a chromosome consist of two identical chromatids?

Compare the roles of tubulin and actin during eukaryotic cell division with the roles of tubulin-like and actin-like proteins during bacterial binary fission.

A kinetochore has been compared to a coupling device that connects a motor to the cargo that it moves. Explain.

What other functions do actin and tubulin carry out? Name the proteins they interact with to do so. (Review Figures 6.21a and 6.26a.)

Figures 6.21a:

Figures 6.26a: