AP Bio Chapter 12 Homework

As in most areas of biology, the study of mitosis and the cell cycle involves a lot of new terminology. Knowing what the different terms mean is essential to understanding and describing the processes occurring in the cell.

1. DNA replication produces two identical DNA molecules, called SISTER CHROMATID(S), which separate during mitosis. 2. After chromosomes condense, the CENTROMERE(S) is the region where the identical DNA molecules are most tightly attached to each other. 3. During mitosis, microtubules attach to chromosomes at the KINETOCHORE(S) 4. In dividing cells, most of the cell's growth occurs during INTERPHASE 5. The MITOTIC SPINDLE(S) is a cell structure consisting of microtubules, which forms during early mitosis and plays a role in cell division. 6. During interphase, most of the nucleus is filled with a complex of DNA and protein in a dispersed form called CHROMATIN 7. In most eukaryotes, division of the nucleus is followed by CYTOKINESIS, when the rest of the cell divides. 8. The CENTROSOME(S) are the organizing centers for microtubules involved in separating chromosomes during mitosis.

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

The cell cycle control systems of cancer cells differ from those of normal cells. Select the best explanation for this fact.

Genetic changes alter the function of the cancer cell's protein products. - The underlying basis of cancer is almost always a change in one or more genes that alters the function of their protein products, resulting in faulty cell cycle control.

I or V

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

Formation of telophase nuclei

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?

B

The lettered circle in Figure 12.1 shows a diploid nucleus with four chromosomes. There are two pairs of homologous chromosomes, one long and the other short. One haploid set is symbolized as black and the other haploid set is gray. The chromosomes in the unlettered circle have not yet replicated. Choose the correct chromosomal conditions for the following stages. 52) What is the correct chromosomal condition at the prometaphase of mitosis?

II

Which number represents DNA synthesis?

II

Which number represents the point in the cell cycle during which the chromosomes are replicated?

What is the final result of mitosis in a human?

genetically identical somatic cells containing 46 chromosomes

Neurons and some other specialized cells divide infrequently because they _____.

have entered into G0

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

in the S phase of the cell cycle

metaphase

kinetochores are motionless in relation to poles of cell

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

lack of appropriate cell death

prometaphase

microtubules attach to kinetochores

The mitotic spindle is a microtubular structure that is involved in _____.

separation of sister chromatids

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

shortening of microtubes

What is true of all cancers?

They have escaped normal cell cycle controls.

Consider an animal cell in which motor proteins in the kinetochores normally pull the chromosomes along the kinetochore microtubules during mitosis.Suppose, however, that during metaphase, this cell was treated with an inhibitor that blocks the function of the motor proteins in the kinetochore, but allows the kinetochore to remain attached to the spindle. The inhibitor has no effect on any other mitotic process, including the function of the nonkinetochore microtubules. Consider three questions concerning the animal cell that has been treated with the inhibitor. Drag the labels to answer the questions. Labels may be used once, more than once, or not at all.

1. Will this cell elongate during mitosis?Yes 2. Will the sister chromatids separate from each other?Yes 3. Will the chromosomes move to the poles of the cell?No The inhibitor does not affect the cleavage of cohesins (the proteins that hold the sister chromatids together), the attachment of the chromosomes to the kinetochore microtubules, or the elongation of the cell due to the nonkinetochore microtubules. The inhibitor only affects the motor protein that pulls the chromosome along the kinetochore microtubule in anaphase. Thus, in the treated cell, the sister chromatids can still separate at the beginning of anaphase due to the fact that the cell is elongating (the centrosomes at the poles of the cell are moving farther apart) and the kinetochore microtubules still connect the chromosomes to the centrosomes. However, because the chromosomes cannot move along the kinetochore microtubules, they will never reach the poles of the cell.

If there are 20 duplicated chromosomes in a cell, how many centromeres are there?

20

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.

As the chromosomes of a parent cell are duplicated and distributed to the two daughter cells during cell division, the structure of the chromosomes changes. Note: Assume that by the end of the M phase, the parent cell has not yet divided to form two daughter cells.

Are sister chromatid present in all or part of this phase?G1-no S-yes G2-yes Beginning of M-yes End of M-no Is the DNA condensed in all or part of this phase? G1- no S-no G2-no Beginning of M-yes End of M-yes Does the cell contain twice as much DNA in this phase as it did in the G1 phase? G1- no S-yes G2-yes Beginning of M- yes End of M-yes

Density-dependent inhibition is a phenomenon in which crowded cells stop dividing at some optimal density and location. This phenomenon involves binding of a cell-surface protein to its counterpart on an adjoining cell's surface. A growth inhibiting signal is sent to both cells, preventing them from dividing. Certain external physical factors can affect this inhibition mechanism.Select the statement that makes a correct prediction about natural phenomena that could occur during the cell cycle to prevent cell growth.

As cells become more numerous, the amount of required growth factors and nutrients per cell becomes insufficient to allow for cell growth.

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

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

III only

At which of the numbered regions would you expect to find cells at metaphase?

Select the part of the cell cycle where the cell actually produces two new identical cells.

Cytokinesis when the cytoplasm divides forming two new cells.

IV

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

For a chemotherapeutic drug to be useful for treating cancer cells, which of the following is most desirable?

It interferes with rapidly dividing cells.

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

MPF

III

MPF reaches its threshold concentration at the end of this stage:

The mitotic spindle is the machinery that guides the separation of chromosomes in anaphase.

Prior to metaphase, the mitotic spindle is constructed by lengthening microtubules that extend from each centrosome. In metaphase, the kinetochore microtubules have attached each pair of sister chromatids, and the nonkinetochore microtubules overlap extensively at the metaphase plate. During anaphase, the kinetochore microtubules shorten as the chromosomes move toward the poles of the cell. At the same time, the nonkinetochore microtubules lengthen and push past each other, elongating the cell. By the end of telophase, all the microtubules associated with the mitotic spindle have disassembled.

What happens if MPF (mitosis-promoting factor) is introduced into immature frog oocytes that are arrested in G2?

The cells enter mitosis

A research team began a study of a cultured cell line. Their preliminary observations showed them that the cell line did not exhibit either density-dependent inhibition or anchorage dependence. What could they conclude right away?

The cells show characteristics of tumors.

The cell cycle represents the coordinated sequence of events in the life of a cell from its formation to its division into two daughter cells. Most of the key events of the cell cycle are restricted to a specific time within the cycle. In this exercise, you will identify when various events occur during the cell cycle. Recall that interphase consists of the G1, S, and G2 subphases, and that the M phase consists of mitosis and cytokinesis.

The first step in preparing for division is to replicate the cell's DNA in the S phase. In the G2 phase, the centrosome replicates. In early M phase, the centrosomes move away from each other toward the poles of the cell, in the process organizing the formation of the mitotic spindle. At the end of the M phase when mitosis is complete, the cell divides (cytokinesis), forming two genetically identical daughter cells. a. non-dividing cells exit cell cycle b. at this point, cell commits to go through the cycle c. DNA replicate d. centrosome replicates e. mitotic spindle begins to form f. cell divides, forming two daughter cells

E

The lettered circle in Figure 12.1 shows a diploid nucleus with 4 chromosomes. There are 2 pairs of homologous chromosomes, one long and the other short. One haploid set is symbolizes as black and the other haploid set is gray. The chromosomes in the unlettered circle have not yet replicated. Chose the correct chromosomal conditions for the following stages. What is the correct chromosomal condition for 1 daughter nucleus at telophase of mitosis?

What are the cellular processes that occur during the stages of mitosis.

The micrographs in Part A show some of the cellular processes that occur during the stages of mitosis. In prophase, the microtubules of the spindle apparatus begin to assemble from individual tubulin subunits. As the identical chromatids of each pair of sister chromatids condense during this stage, they are held together by cohesin proteins. Prometaphase is marked by fragmentation of the nuclear envelope, expansion of the spindle into the nuclear region, and attachment of some spindle fibers to the chromosomes via the kinetochores. Metaphase, marked by the alignment of chromsomes along the metaphase plate, is brought about by kinetochores aligning and then remaining motionless relative to the poles of the cell. In anaphase, the cohesin proteins are cleaved, and the kinetochores move toward the poles of the cell, separating the sister chromatids. As telophase proceeds, the kinetochore microtubules of the spindle disassemble. As the chromosomes reach the poles of the cell, the nuclear envelopes of the two new daughter nuclei form.

Gamma contains more DNA than beta

This data was 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 Of the following, the best conclusion concerning the difference between the S phases for beta and gamma is that:

Are actually in G0 phase

This data was 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 The best conclusion concerning delta is that the cells:

How do cancer cells differ from normal cells?

They can be immortal - Cancer cells can go on dividing indefinitely in culture if they are given a continual supply of nutrients; in essence, they are "immortal." Read about HeLa cells.

anaphase

cohesions break down, kinetochores move toward poles of cell

telophase

cohesions break down, kinetochores move toward poles of cell

Prohphase

cohesions join sister chromatids of duplicated chromosomes, tubulins assemble into spindle microtubules

The microtubule-organizing center found in animal cells is an identifiable structure present during all phases of the cell cycle. Specifically, it is known as the _____.

centrosome

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

cleavage furrow formation and cytokinesis