CHAPTER 9 Test Your Knowledge
Driving Question 1
When and how does normal cell division occur in the body?
By answering the questions below and studying Infographics 9.1 and 9.2 and Up Close: Cell Cycle and Mitosis, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
Following mitosis and cytokinesis, daughter cells are
a. genetically unique.
b. genetically identical to each other.
c. genetically identical to the parent cell.
d. contain half of the parent cell’s chromosomes.
e. b and c
e
In the cell cycle, DNA is replicated during
a. mitosis.
b. G1.
c. S.
d. G2.
e. cytokinesis.
c
What process is critical for embryonic development, wound healing, and replacement of blood cells? (Hint: All these processes require new cells.)
cell division (mitosis and cytokinesis)
During which stage of the cell cycle do sister chromatids separate from each other?
anaphase of mitosis
During which stage of the cell cycle are sister chromatids initially produced?
S phase
USE IT
If a cell fails to replicate its DNA completely, what will happen?
a. It will progress through G2 and mitosis.
b. It will die by apoptosis.
c. It will pause to allow DNA replication to complete.
d. It will stop in S phase and never progress further through the cell cycle.
e. It will stay in interphase indefinitely.
c
Many drugs interfere with cell division. Why shouldn’t pregnant women take these drugs?
The embryo (and later fetus) is growing through the process of mitotic cell division. If the mother took a drug that interfered with cell division, that drug could interfere with normal development of the embryo and fetus, causing birth defects and possibly death of the developing baby.
What would be the result if a cell completed interphase and mitosis but failed to complete cytokinesis–how many cells would there be at that point, and how many chromosomes relative to the parent cell would those cells have?
If a cell completed interphase and mitosis but then did not complete cytokinesis, the result would be a single cell with two nuclei. Each nucleus would have the same number of chromosomes as the parent cell. This means that the single binucleate cell would have twice the number of chromosomes as the parent cell.
Driving Question 2
How do normal cells and cancer cells differ with respect to cell division?
By answering the questions below and studying Infographics 9.2, 9.3, 9.4, and 9.5 and Up Close: Cell Cycle and Mitosis, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
A normal cell that sustains irreparable DNA damage will most likely
a. divide out of control.
b. die by apoptosis.
c. arrest in G2.
d. immediately go back to S phase.
e. stop in S phase and never progress through the cell cycle.
b
Which checkpoint prevents a normal cell from completing its cell cycle if it has not accurately replicated its DNA?
a. interphase (G1–S)
b. interphase (G2–M)
c. mitotic (M)
c. a and b
e. all of the above
b
USE IT
After a bad sunburn, skin usually peels. What process best describes what has happened to the burned skin cells?
a. skin cancer
b. metastasis
c. apoptosis
d. checkpoint failure
e. cytokinesis
c
Cancerous cells may not peel after a bad sunburn. What process has failed in this case?
a. DNA replication
b. signaling to divide
c. cytokinesis
d. checkpoints
e. mitosis
d
Complete the table below by placing a checkmark to indicate which cells will divide in which conditions. Growth factors (GFs) are molecules that signal normal cells to divide.
| Cell Type | No GFs | GFs Present |
| Normal skin cell | – | ✓ |
| Melanoma skin cancer cell | ✓ | ✓ |
Driving Question 3
How are decisions about treatment made for a given cancer patient?
By answering the questions below and studying Infographics 9.6 and 9.7, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
A patient has metastatic melanoma–skin cancer that has spread throughout the body. Is surgery a viable option for this patient? Why or why not?
No. Surgery is not a viable option. Now that the cancer has spread, there is no single tumor that can be surgically removed. There are too many tumors in too many tissues to be able to remove all of them surgically.
Which of the following properties should a promising new ovarian cancer drug have?
a. blocks mitosis in noncancerous cells
b. blocks mitosis in cancerous cells
c. prevents entry into S phase in normal cells
d. enhances the activity of cell cycle checkpoints in noncancerous cells
e. a and b
b
Explain why chemotherapy can cause nausea, diarrhea, and hair loss.
Chemotherapy interferes with all dividing cells, not just cancerous ones. Cells lining the digestive tract normally divide rapidly, and when they are affected by chemotherapy, nausea and diarrhea can occur. Similarly, cells at the base of hair follicles normally divide rapidly, and when chemotherapy drugs interfere with their division, the result is hair loss.
USE IT
Liver cells and neurons rarely, if ever, divide in normal circumstances. The cells lining the digestive tract are replaced by cell division on a regular basis. Explain why chemotherapy frequently causes digestive symptoms but less frequently causes cognitive symptoms.
Chemotherapy interferes with the division of all dividing cells, not just cancerous ones. Because neurons and liver cells do not usually divide in normal circumstances, they are not affected by chemotherapy, and there are no side effects of chemotherapy associated with these cells. However, cells lining the digestive tract divide regularly; chemotherapy interferes with this process, and therefore with the function of the digestive tract, leading to digestive symptoms.
INTERPRETING DATA
Refer to Infographic 9.6 to answer the following questions.
a. If patients with stage 3 ovarian cancer have Taxol added to their chemotherapy regimen, what proportion of them will be alive after 4 years, relative to patients who do not have Taxol added to their chemotherapy regimen?
b. For patients with breast cancer, what proportion will be disease free in 1 year if Taxol is added to their chemotherapy? What proportion will be disease free at 1 year in the absence of Taxol? How do these proportions compare to the same patients at 4 years?
a: On average, 20% of patients receiving chemotherapy (without Taxol) will be alive after 4 years. In contrast, approximately 40% of patients receiving chemotherapy with Taxol will will be alive after 4 years. b: After 1 year, approximately 95% of the Taxol-treated patients will be free of disease, in comparison with approximately 90% of the patients who did not receive Taxol. After 4 years, approximately 80% of the Taxol-treated patients will be disease free, and approximately 75% of the non–Taxol-treated patients will be disease free.
MINI CASE
Rosa has recently been diagnosed with ovarian cancer. Tests show that her cancer has metastasized to her liver, lungs, and brain. For each of the following, discuss how it works to treat cancer and whether or not it would be feasible in Rosa’s case.
a. surgery
b. radiation
c. Taxol
d. chemotherapy without Taxol
a: Surgery physically removes the cancerous cells. Once the cancer has metastasized, as in this case, surgery is not a viable option because there are now too many tumors to remove. In addition to the visible tumors, there may be many more small tumors that have established themselves in other parts of the body. b: Radiation irradiates cancer cells and causes such extensive DNA damage that the cells cannot survive. Radiation is typically focused on specific location, so is not a good option in this case, given the number of distinct tumors. c: Taxol interferes with the microtubules of the mitotic spindle, preventing cell division. Taxol has shown success in ovarian cancer, particularly ovarian cancer that has not responded well to other therapies. d: Chemotherapy in the absence of Taxol is certainly an option. Chemotherapy drugs interfere with cell division. Different drugs have different specific mechanisms of action at the cellular level.
While chemotherapy (alone) and Taxol (alone) are both options in this case, the best option is likely a combination of the two (see Infographic 9.6)
Driving Question 4
How are new cancer drugs developed?
By studying Infographics 9.4, 9.5, and 9.6 and answering the questions below, you should be able to generate an answer for the broader Driving Question above.
KNOW IT
In the production of taxol:
a. What plant was at risk from early demand?
b. What animal was consequently put at risk?
a: the Pacific Yew (Taxus brevifolia); b: the northern spotted owl
If a medically valuable drug is isolated from a rare plant, which of the following steps can be taken to ensure that the drug is made available to patients in need and that the plant is protected from overuse?
a. Try to cultivate the plant on a farm to ensure that there is sufficient supply independent of the plant in its native setting.
b. Try to find a related (and less rare) plant that produces a related compound with similar pharmaceutical activity.
c. Use the structure of the compound to try to make a completely synthetic version of the chemical compound in a lab.
d. Learn more about what the drug is doing in the body and try to design synthetic molecules that might have the same activity.
e. all of the above
e
USE IT
You are a senator sitting on a committee to review cancer drug development. You have heard testimony from a patient with drug-resistant ovarian cancer, an environmentalist, a college student, and a cancer researcher. Summarize their testimony and explain how each witness contributed to your position on the conflict between saving trees and saving lives.
Answers will vary. Some possible testimony:
Patient: Patients with drug-resistant ovarian cancer have almost no options with respect to effective treatment, and their very life depends on a supply of and access to new drugs, even if they are developed from trees.
Environmentalist: The environmentalist is sympathetic to the patient’s perspective, but argues that the tree (the potential source of drugs) is part of an intact ecosystem, supporting a diverse community and providing a variety of “services” both to the environment and to humans (e.g., recreational opportunities in the intact forest, the reduction of CO2 levels by the trees, providing a balanced habitat that will not support the emergence of pests or disease, as can happen when habitats are destroyed). The environmentalist argues that chemists can synthesize chemotherapy drugs in the lab without needing to sacrifice healthy ecosystems.
College student: The college student has a relative with cancer and has taken courses in biology, so can appreciate both points of view presented thus far.
Cancer researcher: The cancer researcher places patient health over all other concerns. The researcher argues that natural products are chemically complex and exceedingly difficult to synthesize in the lab. It could take decades to successfully produce a synthetic drug that will reproduce the effect of a natural product. The researcher wonders if endangered species could be relocated to another environment or a captive breeding program at a zoo, and if there are other plants that could fulfill a in the ecosystem similar to that of the tree in question.
BRING IT HOME
Your mother’s best friend has been diagnosed with ovarian cancer. She was treated with a generic version of Taxol, but her cancer was resistant, and continued to grow. Her doctors have let her know that there aren’t a lot of options for her beyond standard chemotherapy. She wonders why there aren’t more anticancer drugs for her doctors to choose from. What can you tell her about the process of drug discovery and development that would help to explain why there are few novel anticancer drugs?
Some considerations are these: Natural products take huge effort (and time) to collect and screen. Once a natural compound has been identified, it has to be purified and then tested extensively in cultured cells in the lab and in animals. Human clinical trials can take many years, and the results often show that the new drug is no more effective than existing drugs. For this reason, drug companies are very careful about not testing drugs until they have a huge amount of preclinical data in support. Human clinical trials are very expensive, and there may not always be funds to test all the possible drugs. Promising drugs may show undue adverse side effects, requiring chemical modification both to reduce side effects and to improve delivery of the drug to tumors in the body.