Chapter 17 Study Questions

A bacterium is infected with an experimentally constructed bacteriophage composed of the T2 phage protein coat and T4 phage DNA. The new phages produced will have A) a mixture of the DNA and proteins of both phages. B) T4 protein and T4 DNA. C) T4 protein and T2 DNA. D) T2 protein and T2 DNA. E) T2 protein and T4 DNA

B

Emerging viruses arise by A)the spread of existing viruses more widely within their host species. B) the spread of existing viruses to new host species. C) mutation of existing viruses. D) all of the above E) none of the above

D

Which of the following is the best predictor of how much damage a virus causes? A) ability of the infected cell to carry on translation B) whether the infected cell produces viral protein C) whether the viral mRNA can be transcribed D) ability of the infected cell to undergo normal cell division E) how much toxin the virus produces

D

A human pandemic is A) a virus that increases in mortality rate as it spreads. B) a viral disease that can infect multiple species. C) a flu that kills more than 1 million people. D) a viral disease that infects all humans. E) an epidemic that extends around the world.

E

Antiviral drugs that have become useful are usually associated with which of the following properties? A) removal of viral proteins B) ability to remove all viruses from the infected host C) removal of viral mRNAs D) prevention of the host from becoming infected E) interference with viral replication

E

Most molecular biologists think that viruses originated from fragments of cellular nucleic acid. Which of the following observations supports this theory? A) Viruses can infect both prokaryotic and eukaryotic cells. B) Viruses contain either DNA or RNA. C) Viruses can reproduce only inside host cells. D) Viruses are enclosed in protein capsids rather than plasma membranes. E) Viral genomes are usually similar to the genome of the host cell.

E

Which of the following characteristics, structures, or processes is common to both bacteria and viruses? A) cell division B) metabolism C) ribosomes D) independent existence E) genetic material composed of nucleic acid

E

Which of the following describes plant virus infections? A) They can be controlled by the use of antibiotics. B) They are seldom spread by insects. C) They can never be passed vertically. D) They have little effect on plant growth. E) They are spread via the plasmodesmata.

E

Which of the following is the most probable fate of a newly emerging virus that causes high mortality in its host? A) The new virus replicates quickly and undergoes rapid adaptation to a series of divergent hosts. B) A change in environmental conditions such as weather patterns quickly forces the new virus to invade new areas. C) It is able to spread to a large number of new hosts quickly because the new hosts have no immunological memory of them. D) Sporadic outbreaks will be followed almost immediately by a widespread pandemic. E) The newly emerging virus will die out rather quickly or will mutate to be far less lethal.

E

Refer to the treatments listed below to answer the following questions. You isolate an infectious substance that is capable of causing disease in plants, but you do not know whether the infectious agent is a bacterium, virus, viroid, or prion. You have four methods at your disposal that you can use to analyze the substance in order to determine the nature of the infectious agent. I. treating the substance with nucleases that destroy all nucleic acids and then determining whether it is still infectious II. filtering the substance to remove all elements smaller than what can be easily seen under a light microscope III. culturing the substance by itself on nutritive medium, away from any plant cells IV. treating the sample with proteases that digest all proteins and then determining whether it is still infectious If you already knew that the infectious agent was either bacterial or viral, which treatment would allow you to distinguish between these two possibilities? A) III B) II C) I D) IV E) either II or IV

A

Viral envelopes can best be analyzed with which of the following techniques? A) antibodies against specific proteins not found in the host membranes B) use of 15N to label specific nucleotides C) use of plaque assays for quantitative measurement of viral titer D) DNA staining and visualization with the light microscope E) immunofluorescent tagging of capsid proteins

A

A researcher lyses a cell that contains nucleic acid molecules and capsomeres of tobacco mosaic virus (TMV). The cell contents are left in a covered test tube overnight. The next day this mixture is sprayed on tobacco plants. Which of the following would be expected to occur? A) The plants would develop symptoms typically produced by viroids. B) The plants would develop the typical symptoms of TMV infection. C) The plants would become infected, but the sap from these plants would be unable to infect other plants. D) The plants would develop some but not all of the symptoms of the TMV infection. E) The plants would not show any disease symptoms.

B

Use the following information to answer the few questions. The herpesviruses are very important enveloped DNA viruses that cause disease in all vertebrate species and in some invertebrates such as oysters. Some of the human ones are herpes simplex virus (HSV) types I and II, causing facial and genital lesions, and the varicella zoster virus (VSV), causing chicken pox and shingles. Each of these three actively infects nervous tissue. Primary infections are fairly mild, but the virus is not then cleared from the host; rather, viral genomes are maintained in cells in a latent phase. The virus can then reactivate, replicate again, and be infectious to others. If scientists are trying to use what they know about HSV to devise a means of protecting other people from being infected, which of the following would have the best chance of lowering the number of new cases of infection? A) education about avoiding sources of infection B) interference with new viral replication in preexisting cases C) medication that destroys surface HSV before it gets to neurons D) vaccination of all persons with preexisting cases E) treatment of the HSV lesions to shorten the breakout

B

Which of the following can be effective in preventing the onset of viral infection in humans? A) taking antibiotics B) getting vaccinated C) applying antiseptics D) taking nucleoside analogs that inhibit transcription E) taking vitamins

B

Which of the following series best reflects what we know about how the flu virus moves between species? A) The flu virus in a pig is mutated and replicated in alternate arrangements so that humans who eat the pig products can be infected. B) An animal such as a pig is infected with more than one virus, genetic recombination occurs, the new virus mutates and is passed to a new species such as a bird, and the virus mutates and can be transmitted to humans. C) A flu virus from a human epidemic or pandemic infects birds; the birds replicate the virus differently and then pass it back to humans. D) An influenza virus gains new sequences of DNA from another virus, such as a herpesvirus; this enables it to be transmitted to a human host. E) An avian flu virus undergoes several mutations and rearrangements such that it is able to be transmitted to other birds and then to humans.

B

Which of the following statements describes the lysogenic cycle of lambda (λ) phage? A) Most of the prophage genes are activated by the product of a particular prophage gene. B) The phage genome replicates along with the host genome. C) After infection, the viral genes immediately turn the host cell into a lambda-producing factory, and the host cell then lyses. D) Certain environmental triggers can cause the phage to exit the host genome, switching from the lytic to the lysogenic. E) The phage DNA is incorporated by crossing over into any nonspecific site on the host cell's DNA.

B

Why do RNA viruses appear to have higher rates of mutation? A) RNA viruses can incorporate a variety of nonstandard bases. B) Replication of their genomes does not involve proofreading. C) RNA nucleotides are more unstable than DNA nucleotides. D) RNA viruses replicate faster. E) RNA viruses are more sensitive to mutagens.

B

The host range of a virus is determined by A) the enzymes carried by the virus. B) the enzymes produced by the virus before it infects the cell. C) the proteins on its surface and that of the host. D) whether its nucleic acid is DNA or RNA. E) the proteins in the host's cytoplasm.

C

Use the following information to answer the question below. Some viruses can be crystallized and their structures analyzed. One such virus is yellow mottle virus, which infects beans. This virus has a single-stranded RNA genome containing about 6,300 nucleotides. Its capsid is 25-30 nm in diameter and contains 180 identical capsomeres. If the yellow mottle virus capsid has 20 facets, how many proteins form each facet? A) 5 B) 180 C) 9 D) 1 E) 20

C

Which of the following accounts for someone who has had a herpesvirus-mediated cold sore or genital sore getting flare-ups for the rest of his or her life? A) co-infection with an unrelated virus that causes the same symptoms B) re-infection by a closely related herpesvirus of a different strain C) copies of the herpesvirus genome permanently maintained in host nuclei D) re-infection by the same herpesvirus strain E) copies of the herpesvirus genome permanently maintained in host cell cytoplasm

C

Which viruses have single-stranded RNA that acts as a template for DNA synthesis? A) bacteriophages B) viroids C) retroviruses D) lytic phages E) proviruses

C

In many ways, the regulation of the genes of a particular group of viruses will be similar to the regulation of the host genes. Therefore, which of the following would you expect of the genes of the bacteriophage? A) reliance on transcription activators B) utilization of eukaryotic polymerases C) regulation via acetylation of histones D) control of more than one gene in an operon E) positive control mechanisms rather than negative

D

RNA viruses require their own supply of certain enzymes because A) these enzymes penetrate host cell membranes. B) these enzymes cannot be made in host cells. C) these enzymes translate viral mRNA into proteins. D) host cells lack enzymes that can replicate the viral genome. E) host cells rapidly destroy the viruses.

D

Use the following information to answer the few questions. The herpesviruses are very important enveloped DNA viruses that cause disease in all vertebrate species and in some invertebrates such as oysters. Some of the human ones are herpes simplex virus (HSV) types I and II, causing facial and genital lesions, and the varicella zoster virus (VSV), causing chicken pox and shingles. Each of these three actively infects nervous tissue. Primary infections are fairly mild, but the virus is not then cleared from the host; rather, viral genomes are maintained in cells in a latent phase. The virus can then reactivate, replicate again, and be infectious to others. In order to be able to remain latent in an infected live cell, HSV must be able to shut down what process? A) interaction with histones B) DNA replication C) all immune responses D) apoptosis of a virally infected cell E) transcription of viral genes

D

What is the function of reverse transcriptase in retroviruses? A) It translates viral RNA into proteins. B) It converts host cell RNA into viral DNA. C) It uses viral RNA as a template for making complementary RNA strands. D) It uses viral RNA as a template for DNA synthesis. E) It hydrolyzes the host cell's DNA.

D

Which of the following is characteristic of the lytic cycle? A) The viral genome replicates without destroying the host. B) Many bacterial cells containing viral DNA are produced. C) The virus-host relationship usually lasts for generations. D) A large number of phages are released at a time. E) Viral DNA is incorporated into the host genome.

D

Refer to the treatments listed below to answer the following questions. You isolate an infectious substance that is capable of causing disease in plants, but you do not know whether the infectious agent is a bacterium, virus, viroid, or prion. You have four methods at your disposal that you can use to analyze the substance in order to determine the nature of the infectious agent. I. treating the substance with nucleases that destroy all nucleic acids and then determining whether it is still infectious II. filtering the substance to remove all elements smaller than what can be easily seen under a light microscope III. culturing the substance by itself on nutritive medium, away from any plant cells IV. treating the sample with proteases that digest all proteins and then determining whether it is still infectious If you already knew that the infectious agent was either a viroid or a prion, which treatment would allow you to distinguish between these two possibilities? A) I only B) II only C) IV only D) III only E) either I or IV

E

The difference between vertical and horizontal transmission of plant viruses is that A) vertical transmission is the spread of viruses from trees and tall plants to bushes and other smaller plants, and horizontal transmission is the spread of viruses among plants of similar size. B) vertical transmission is the transfer of DNA from a plant of one species to a plant of a different species, and horizontal transmission is the spread of viruses among plants of the same species. C) vertical transmission is the transfer of DNA from one type of plant virus to another, and horizontal transmission is the exchange of DNA between two plant viruses of the same type. D) vertical transmission is the spread of viruses from the upper leaves to the lower leaves of the plant, and horizontal transmission is the spread of a virus among leaves at the same general level. E) vertical transmission is transmission of a virus from a parent plant to its progeny, and horizontal transmission is one plant spreading the virus to another plant.

E

Use the following information to answer the few questions. The herpesviruses are very important enveloped DNA viruses that cause disease in all vertebrate species and in some invertebrates such as oysters. Some of the human ones are herpes simplex virus (HSV) types I and II, causing facial and genital lesions, and the varicella zoster virus (VSV), causing chicken pox and shingles. Each of these three actively infects nervous tissue. Primary infections are fairly mild, but the virus is not then cleared from the host; rather, viral genomes are maintained in cells in a latent phase. The virus can then reactivate, replicate again, and be infectious to others. In electron micrographs of HSV infection, it can be seen that the intact virus initially reacts with cell-surface proteoglycans, then with specific receptors. This is later followed by viral capsids docking with nuclear pores. Afterward, the capsids go from being full to being "empty." Which of the following best fits these observations? A) The viral envelope is not required for infectivity, since the envelope does not enter the nucleus. B) Viral capsids are needed for the cell to become infected; only the capsids enter the nucleus. C) Only the genetic material of the virus is involved in the cell's infectivity, and is injected like the genome of a phage. D) The viral capsid mediates entry into the cell, and only the genomic DNA enters the nucleus, where it may or may not replicate. E) The viral envelope mediates entry into the cell, the capsid enters into the nuclear membrane, and the genome is all that enters the nucleus.

E