1. The reverse transcriptase enzyme is active in which class of viruses? a. Positive-strand RNA viruses b. Double-stranded DNA viruses c. Retroviruses d. Negative-strand RNA viruses
The correct answer is c—
A. Answer a is incorrect. Positive-strand RNA viruses do not require the reverse transcriptase enzyme.
The correct answer is c—
B. Answer b is incorrect. DNA viruses do not require a reverse transcriptase enzyme
The correct answer is c—Retroviruses
C. Answer c is correct. Retroviruses utilize reverse transcriptase to convert their
RNA genomes into DNA.
The correct answer is c—
D. Answer d is incorrect. Negative-strand RNA viruses do not require reverse transcriptase.
2. Which of the following is not part of a virus? a. Capsid b. Ribosomes c. Genetic material d. All of the above are found in viruses
The correct answer is b—
A. Answer a is incorrect. Most viruses contain a capsid. See Figure 27.1.
The correct answer is b—Ribosomes
B. Answer b is correct. Viruses lack ribosomes.
The correct answer is b—
C. Answer c is incorrect. All viruses contain either RNA or DNA as genetic material.
The correct answer is b—
D. Answer d is incorrect. One of the above answers is not found in a virus.
3. Which of the following is common in animal viruses but not in bacteriophages? a. DNA b. Capsid c. Envelope d. Icosahedral shape
The correct answer is c—
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A. Answer a is incorrect. DNA is found in both animal viruses and bacteriophages.
The correct answer is c—
B. Answer b is incorrect. A capsid is found in both animal viruses and bacteriophages.
The correct answer is c—Envelope
C. Answer c is correct. Envelopes are found on many viruses that infect animals, but is not common in bacteriophages.
The correct answer is c—
D. Answer d is incorrect. Specific shapes are fond in both animal viruses and bacteriophages.
4. Which of the following would NOT be part of the life cycle of a lytic virus? a. Macromolecular synthesis b. Attachment to host cell c. Assembly of progeny virus d. Integration into the host genome
The correct answer is d—
A. Answer a is incorrect. Macromolecular synthesis is part of the lytic cycle. See
Figure 27.5.
The correct answer is d—
B. Answer b is incorrect. Attachment to the host cell is part of the lytic cycle. See
Figure 27.5.
The correct answer is d—
C. Answer c is incorrect. Assembly of progeny virus is part of the lytic cycle. See
Figure 27.5.
The correct answer is d—Integration into the host genome
D. Answer d is correct. Integration into the host genome is part of the lysogenic, not lytic, cycles. See Figure 27.5.
5. A process by which a virus may change a benign bacterium into a virulent strain is called_______. a. induction b. phage conversion c. lysogeny d. replication
The correct answer is b—
A. Answer a is incorrect. Induction is a step of the lysogenic cycle.
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The correct answer is b—phage conversion
B. Answer b is correct. Phage conversion introduces new genes into a benign bacterium; sometimes making them pathogenic.
The correct answer is b—
C. Answer c is incorrect. Lysogeny is the integration of a virus into the host genome.
The correct answer is b—
D. Answer d is incorrect. Replication involves the copying of the genetic material.
6. Prior to entry, the _________ glycoprotein of the HIV virus recognizes the
______ receptor on the surface of the macrophage. a. CCR5; gp120 b. CXCR4; CCR5 c. CD4; CCR5 d. gp120; CD4
The correct answer is d—
A. Answer a is incorrect. Refer to Figure 27.6.
The correct answer is d—
B. Answer b is incorrect. Refer to Figure 27.6.
The correct answer is d—
C. Answer c is incorrect. Refer to Figure 27.6.
The correct answer is d—gp120; CD4
D. Answer d is correct.
7. The varying degrees of resistance to HIV in populations have been suggested to be related to the patterns of smallpox outbreaks over human history. This explanation hinges on— a. the similarity in the genomes of the two viruses b. the fact that both viruses use reverse transcriptase c. both viruses using the same receptor to bind to host cells d. both viruses compromising the immune system
The correct answer is c—
A. Answer a is incorrect. HIV is a retrovirus and smallpox is a DNA virus.
The correct answer is c—
B. Answer b is incorrect. HIV requires reverse transcriptase in its life cycle, but smallpox does not.
The correct answer is c—both viruses using the same receptor to bind to host cells
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C. Answer c is correct. It is thought that both viruses may bind to the same receptor to infect cells.
The correct answer is c—
D. Answer d is incorrect. Smallpox does not compromise the immune system.
8. Current research has focused on blocking what receptor on the T cell lymphocyte in order to protect it from infection by the HIV virus? a. gp120 b. CD4 c. CCR5 d. CD5
The correct answer is c—
A. Answer a is incorrect. This is a glycoprotein on the HIV virus.
The correct answer is c—
B. Answer b is incorrect. While this is a receptor, it is not the focus of current research.
The correct answer is c—
C. Answer c is correct.
The correct answer is c—
D. Answer d is incorrect.
9. Which of the following HIV treatments prevent the formation of a functional capsid? a. Vaccine therapy b. Chemokines c. Nucleoside analogs d. Protease inhibitors
The correct answer is d—
A. Answer a is incorrect. Vaccine therapy does not address this aspect of HIV infection.
The correct answer is d—
B. Answer b is incorrect. The use of chemokines does not address this aspect of HIV infection.
The correct answer is d—
C. Answer c is incorrect. The use of nucleoside analogs does not address this aspect of HIV infection.
The correct answer is d—Protease inhibitors
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D. Answer d is correct. Protease inhibitors may block capsid formation in some cases.
10. Which of the following viruses routinely exhibit antigenic shifts, making vaccination programs difficult? a. HIV b. Influenza c. Hantavirus d. Filoviruses
The correct answer is b—
A. Answer a is incorrect. HIV does not exhibit an antigenic shift.
The correct answer is b—Influenza
B. Answer b is correct. Antigenic shifts are responsible for most major influenza outbreaks.
The correct answer is b—
C. Answer c is incorrect. It is unknown if the hantavirus utilizes an antigenic shift.
The correct answer is b—
D. Answer d is incorrect. It is unknown if the filoviruses utilize an antigenic shift.
11. Activation of oncogenes to cause cancer may be caused by the action of a
________. a. virus b. viroid c. prion d. bacteria
The correct answer is a—virus
A. Answer a is correct. Viral interaction with the host genome may activate oncogenes.
The correct answer is a—
B. Answer b is incorrect. There is currently no evidence that viroids activate oncogenes.
The correct answer is a—
C. Answer c is incorrect. There is currently no evidence that prions activate oncogenes.
The correct answer is a—
D. Answer d is incorrect. There is currently no evidence that bacteria activate oncogenes.
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12. Prions are responsible for which of the following? a. Mad cow disease b. Scrapie c. Variant Creutzfeldt-Jacob disease d. All of the above
The correct answer is d—
A. Answer a is incorrect. Prions cause diseases in addition to this.
The correct answer is d—
B. Answer b is incorrect. Prions cause diseases in addition to this.
The correct answer is d—
C. Answer c is incorrect. Prions cause diseases in addition to this.
The correct answer is d—All of the above
D. Answer d is correct. Prions are responsible for all of the diseases in the list.
13. An infectious RNA without a capsid or envelope is called a ____________. a. prion b. bacteriophage c. viroid d. virus
The correct answer is c—
A. Answer a is incorrect. Prions are proteins.
The correct answer is c—
B. Answer b is incorrect. Bacteriophages are a form of virus that infects bacteria.
The correct answer is c—
C. Answer c is correct. The RNA molecule is often circular in viroids.
The correct answer is c—
D. Answer d is incorrect. Viruses possess a protein coat called a capsid.
14. SARS is associated with what form of virus? a. Hantavirus b. Coronavirus c. Filovirus d. Influenza virus
The correct answer is b—
A. Answer a is incorrect. This is not the virus responsible for SARS.
The correct answer is b—Coronavirus
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B. Answer b is correct. This is the virus that is responsible for SARS.
The correct answer is b—
C. Answer c is incorrect. This is not the virus responsible for SARS.
The correct answer is b—
D. Answer d is incorrect. This is not the virus responsible for SARS.
15. A nonliving, infectious particle that lacks any nucleic acids or an envelope, and contains only amino acids, would be classified with the _______. a. prions b. viruses c. viroids d. bacteria
The correct answer is a—prions
A. Answer a is correct. This is the definition of a prion.
The correct answer is a—
B. Answer b is incorrect. Viruses contain nucleic acids.
The correct answer is a—
C. Answer c is incorrect. Viroids contain the nucleic acid RNA.
The correct answer is a—
D. Answer d is incorrect. Bacteria are living organisms.
Challenge Questions
1. E. coli lysogens derived from infection by phage lambda can be induced to form progeny viruses by exposure to radiation. The inductive event is the destruction of a repressor protein that keeps the prophage genome unexpressed. What might be the normal role of the protein that recognizes and destroys the lambda repressor?
Answer
—A set of genes that are involved in the response to DNA damage are normally induced by the same system. The protein involved destroys a repressor that keeps DNA repair genes unexpressed. Lambda has evolved to use this system to its advantage.
2. Most biologists believe that viruses evolved following the origin of the first cells?
Why do you think that this is the case?
Answer— Since viruses require the replication machinery of a host cell to replicate, it is unlikely that they existed before the origin of the first cells.
3. In 1971 President Nixon declared a “War on Cancer.” Although significant advances have been made in the past three decades, the war is far from over. The
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discovery that viruses may be responsible for some forms of cancer have both helped and hindered the battle. Why?
Answer— The discovery that viruses may be responsible for some forms of cancer means that it is possible that the use of vaccinations may reduce the rates of certain cancers.
However, since the number of viruses is immense, it is unlikely that we will ever develop methods of protecting against all virus-caused cancers.
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