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Inquiry Questions

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Self Test

1). Tumor-suppressor genes includes p53 and Rb. How would a "gain-of-function" mutation likely affect the cell?
    a). The cell would divide constantly because of the loss of cell cycle repression.
    b). The cell would divide much less frequently because of the extra cell cycle repression.
    c). The cell would divide normally because these genes have no effect on cell cycle control.
    d). The cell would commit suicide by apoptosis.
Answer: b

2). In lab, you are studying cell cycle control in the fission yeast, S. pombe. A student finds a new mutant that she wants to call "giant" because the cells are much larger than normal (suggesting that it is not dividing normally). What type of mutation do you think your student has isolated?
    a). a loss-of-function mutation in a tumor-suppressor gene
    b). a loss-of-function mutation in a cellular proto-oncogene
    c). a gain-of-function mutation in a tumor-suppressor gene
    d). a gain-of-function mutation in a cellular proto-oncogene
    e). Both a and d are possible.
    f). Both b and c are possible.
Answer: f

3). Which of the following would be an effective approach to a new cancer therapy?
    a). finding a way to stabilize p53 specifically in tumor cells
    b). preventing nucleotide synthesis in tumor cells
    c). inactivating the HER2 receptor on tumor cells
    d). inhibiting growth of new blood vessels with endostatin
    e). All of the above would help to fight cancer.
Answer: e

4). How would the cell cycle be affected if you removed the phosphorylation sites in the Rb protein?
    a). The cell cycle would not be affected because pRb is not phosphorylated normally.
    b). The cell cycle would be blocked in G1.
    c). The cell cycle would be blocked in G2.
    d). The cell cycle would be shorter.
Answer: b

5). Embryonic stem (ES) cells are an attractive source of material for therapeutic cloning because
    a). they can be induced to assume any cell fate.
    b). ES cells are not targets for the host immune response, so tissue rejection is not an issue.
    c). there are no other sources of stem cells to use for therapeutic cloning, so ES cells are the only solution.
    d). ES cells will not work as a source of tissue for cloning.
Answer: a

6). How would growing cells in the presence of methyladenosine affect the mismatch repair system?
    a). The repair system would only repair half of the errors introduced by DNA polymerase.
    b). There would be no repair of mismatched DNA.
    c). Mismatch repair would be normal, but excision repair would fail.
    d). Methyladenosine would prevent DNA replication, so there would be no need for mismatch repair.
Answer: a

7). Too much time in a tanning booth probably causes DNA damage to epithelial cells. The most likely effect would be
    a). depurination.
    b). pyrimidine dimers.
    c). deamination.
    d). single-stranded nicks in the phosphodiester backbone.
Answer: b

8). Using a "car and driver" analogy, which of the following accurately describes the role of tumor-suppressor genes and proto-oncogenes in normal cells?
    a). Tumor-suppressor genes are the gas pedal, while proto-oncogenes are the brakes.
    b). Tumor-suppressor genes are the brakes while proto-oncogenes are the gas.
    c). Both tumor-suppressor genes and proto-oncogenes are like the gas, but tumor-suppressors are like turbo and proto-oncogenes are like a regular carburetor.
    d). Tumor-suppressor genes are like the steering wheel, and proto-oncogenes are like the turn signals.
Answer: b

9). During the early years of cancer research, there were two schools of thought regarding the causes of cancer: 1) that cancer was caused entirely by environmental factors, and 2) that cancer was caused by genetic factors. Which was correct?
    a). #1 because we have identified many potential carcinogens
    b). #2 because we know of many proto-oncogenes
    c). #2 because we know of many tumor-suppressor genes
    d). Both were correct; most chemical carcinogens function by altering genes.
Answer: d
10. If you found a specific chromosomal deletion in the genome from a tumor, what could be the cause of this specific cancer?
    a). The deletion likely affected a tumor-suppressor gene, leading to a loss of function in the tumor cells.
    b). The deletion likely affected a proto-oncogene, leading to a loss of function in the tumor cells.
    c). The deletion likely affected a tumor-suppressor gene, leading to a gain of function in the tumor cells.
    d). The deletion likely affected a proto-oncogene, leading to a gain of function in the tumor cells.
Answer: a

Test Your Visual Understanding

1). If you were to observe two bacterial cells as shown here, what would you suggest is happening?
Answer: The two bacterial cells are exchanging genetic material in a process called conjugation. One cell extends a pilus to the other, forming a bridge between the two cells. The cells are drawn close together and the DNA in the plasmid of one cell is copied and sent through the conjugation bridge to the other cell.

Apply Your Knowledge

1). The data in table 20.3 show the incidence of specific cancers following exposure to environmental carcinogens. Discuss how this type of chemical exposure leads to such a high proportion of skin and lung tumors.
Answer: The skin is the outside barrier between the body and the environment, as is the mucous membrane that lines the respiratory tract to the lungs. Because of this, chemicals in the environment come into contact with these areas first and most frequently. As a result, cells of the skin and lungs are more prone to genetic damage from these chemicals, which can lead to cancer.

2). Pretend that you are preparing for a debate about the use of embryonic stem cells for therapeutic cloning, and list three pros and cons of this technology.
Answer: There are many pros and cons that could be included in this answer. Here are but a few. The pros: 1). Using pluripotent embryonic stem cells holds the possibility of curing chronic diseases such as Parkinson disease and type I diabetes which would improve the quality of life for so many. 2). Curing these and other chronic diseases would reduce healthcare costs, both the cost of medical treatments and long-term care that many of these patients require as they age. 3). This technology would reduce the number of organ transplants that are performed each year and reduce the wait of patients on lists waiting for organ transplants. Also, would eliminate the need for organ transplant patients to use immunosuppressant drugs, which reduces rejection of transplanted tissues but also make the person susceptible to infections.
The cons: 1). This technology involves the killing of an embryo, which is deemed immoral by many. Even in therapeutic cloning that uses the nucleus of the patient (needed to reduce rejection by the body), an embryo is still formed and killed in the process. 2). Many of these chronic diseases are genetic disorders and by using the patient's nucleus, the DNA of the embryonic stem cells still carries the mutations that caused the genetic disorder and so the transplanted cells may ultimately produce the same disorder in the replaced tissue. 3). This opens the door for abuses of the technology to be carried over into reproductive cloning that is banned in most countries.

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