Chapter 19

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3) Which of the following supports the argument that viruses are nonliving?

A) They are not cellular.
B) Their DNA does not encode proteins.
C) They have RNA rather than DNA.

D) They do not evolve.

Answer: A

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4) Viruses _____.
A) manufacture their own ATP, proteins, and nucleic acids
B) use the host cell to copy themselves and make viral proteins
C) use the host cell to copy themselves and then viruses synthesize their own proteins

D) metabolize food and produce their own ATP

Answer: B

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5) What is the main structural difference between enveloped and nonenveloped viruses?
A) Enveloped viruses have their genetic material enclosed by a layer made only of protein.

B) Nonenveloped viruses have only a phospholipid membrane, while enveloped viruses have two membranes, the other one being a protein capsid.
C) Enveloped viruses have a phospholipid membrane outside their capsid, whereas nonenveloped viruses do not have a phospholipid membrane.
D) Both types of viruses have a capsid and phospholipid membrane; but in the nonenveloped virus the genetic material is between these two membranes, while in the enveloped virus the genetic material is inside both membranes.

Answer: C

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6) The host range of a virus is determined by _____.

A) the enzymes carried by the virus
B) whether its nucleic acid is DNA or RNA
C) the proteins in the host's cytoplasm

D) the proteins on its surface and that of the host

Answer: D

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7) Which of the following accounts for someone who has had regular herpesvirus-mediated cold sore or genital sore flare-ups?
A) re-infection by a closely related herpesvirus of a different strain
B) re-infection by the same herpesvirus strain

C) copies of the herpesvirus genome permanently maintained in host nuclei
D) copies of the herpesvirus genome permanently maintained in host cell cytoplasm

Answer: C

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8) 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 a bacteriophage?
A) regulation via acetylation of histones

B) positive control mechanisms rather than negative

C) control of more than one gene in an operon
D) reliance on transcription activators

Answer: C

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9) Which of the following is characteristic of the lytic cycle?

A) Viral DNA is incorporated into the host genome.
B) The viral genome replicates without destroying the host.

C) A large number of phages are released at a time.

D) The virus—host relationship usually lasts for generations.

Answer: C

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10) Which of the following statements describes the lysogenic cycle of lambda (λ) phage?

A) After infection, the viral genes immediately turn the host cell into a lambda-producing factory, and the host cell then lyses.
B) Most of the prophage genes are activated by the product of a particular prophage gene.

C) The phage genome replicates along with the host genome.

D) The phage DNA is copied and exits the cell as a phage.

Answer: C

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11) Which viruses have single-stranded RNA that acts as a template for DNA synthesis?

A) proviruses
B) viroids
C) bacteriophages

D) retroviruses

Answer: D

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12) What is the function of reverse transcriptase in retroviruses?

A) It uses viral RNA as a template for DNA synthesis.
B) It converts host cell RNA into viral DNA.
C) It translates viral RNA into proteins.

D) It uses viral RNA as a template for making complementary RNA strands.

Answer: A

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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 6300 nucleotides. Its capsid is 25-30 nm in diameter and contains 180 identical capsomeres.

15) If the yellow mottle virus begins its infection of a cell by using its genome as mRNA, which of the following would you expect to be able to measure?
A) replication rate
B) transcription rate

C) translation rate
D) formation of new transcription factors

Answer: C

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The herpes viruses are important enveloped DNA viruses that cause disease in vertebrates and in some invertebrates such as oysters. Some of the human forms 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 later reactivate, replicate again, and infect others.

16) 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) Viral capsids are needed for the cell to become infected; only the capsids enter the nucleus.

B) The viral envelope is not required for infectivity, since the envelope does not 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 envelope mediates entry into the cell, the capsid mediates entry into the nuclear membrane, and the genome is all that enters the nucleus.

Answer: D

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17) Poliovirus is an RNA virus of the picornavirus group, which uses its RNA as mRNA. At its 5' end, the RNA genome has a viral protein (VPg) instead of a cap. This is followed by a

nontranslated leader sequence, and then a single long protein-coding region (~7000 nucleotides), followed by a poly-A tail. Observations were made that used radioactive amino acid analogues. Short period use of the radioactive amino acids result in labeling of only very long proteins, while longer periods of labeling result in several different short polypeptides. What conclusion is most consistent with the results of the radioactive labeling experiment?

A) Host cell ribosomes only translate the viral code into short polypeptides.
B) The RNA is only translated into a single long polypeptide, which is then cleaved into shorter ones.
C) The RNA is translated into short polypeptides, which are subsequently assembled into large ones.
D) The large radioactive polypeptides are coded by the host, whereas the short ones are coded for by the virus.

Answer: B

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20) The virus genome and viral proteins are assembled into virions (virus particles) during _____.
A) the lytic cycle and the lysogenic cycle in all known host organisms
B) the lysogenic cycle only

C) the lytic cycle only
D) the lytic cycle in all host organisms but the lysogenic cycle only in bacteria

Answer: C

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21) Which of the following viruses would most likely have reverse transcriptase?

A) an RNA-based lytic virus
B) an RNA-based lysogenic virus
C) a DNA-based lytic virus

D) a DNA-based lysogenic virus

Answer: B

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22) If a viral host cell has a mutation that interferes with the addition of carbohydrates to proteins in the Golgi, which of the following could likely result?
A) The viral envelope proteins would not be glycosylated and might not arrive at the host plasma membrane.

B) The viral capsid proteins would not be glycosylated and might not arrive at the host plasma membrane.
C) The viral core proteins would not be glycosylated and might not arrive at the host plasma membrane.

D) The virus would be unable to reproduce within the host cell.

Answer: A

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23) HIV is inactivated in the laboratory after a few minutes of sitting at room temperature, but the flu virus is still active after sitting for several hours. What are the practical consequences of these findings?
A) HIV can be transmitted more easily from person to person than the flu virus

B) The flu virus can be transmitted more easily from person to person than HIV
C) This property of HIV makes it more likely to be a pandemic than the flu virus

D) Disinfecting surfaces is more important to reduce the spread of HIV than the flu

Answer: B

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24) Viruses use the host's machinery to make copies of themselves. However, some human viruses require a type of replication that humans do not normally have. For example, humans normally do not have the ability to convert RNA into DNA. How can these types of viruses infect humans, when human cells cannot perform a particular role that the virus requires?

A) The virus causes mutations in the human cells, resulting in the formation of new enzymes that are capable of performing these roles.
B) The viral genome codes for specialized enzymes not in the host.
C) The virus infects only those cells and species that can perform all the replication roles necessary.

D) Viruses can stay in a quiescent state until the host cell evolves this ability.

Answer: B

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25) The first class of drugs developed to treat AIDS, such as AZT, were known as reverse transcriptase inhibitors. They worked because they _____.
A) targeted and destroyed the viral genome before it could be reverse transcribed into DNA B) bonded to the dsDNA genome of the virus in such a way that it could not separate for replication to occur

C) bonded to the viral reverse transcriptase enzyme, thus preventing the virus from making a DNA copy of its RNA genome
D) prevented host cells from producing the enzymes used by the virus to replicate its genome

Answer: C

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26) A virus consisting of a single strand of RNA, which is transcribed into complementary DNA, is a _____.
A) protease
B) retrovirus

C) RNA replicase virus
D) nonenveloped virus

Answer: B

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27) Which of the following could use reverse transcriptase to transcribe its genome?

A) ssRNA
B) dsRNA
C) ssDNA

D) dsDNA

Answer: A

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28) To make a vaccine against mumps, measles, or rabies, which type of viruses would be useful?
A) dsDNA viruses
B) negative-sense ssRNA viruses

C) positive-sense ssRNA viruses
D) dsRNA viruses

Answer: B

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29) Which of the following human diseases is caused by a virus that requires reverse transcriptase to transcribe its genome inside the host cell?
A) herpes
B) AIDS

C) smallpox
D) influenza

Answer: B

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30) Why do RNA viruses appear to have higher rates of mutation?

A) RNA nucleotides are more unstable than DNA nucleotides.
B) Replication of their genomes does not involve proofreading.

C) RNA viruses can incorporate a variety of nonstandard bases.

D) RNA viruses are more sensitive to mutagens.

Answer: B

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31) 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. We expect that the plants would _____.
A) develop some but not all of the symptoms of the TMV infection
B) develop the typical symptoms of TMV infection
C) not show any disease symptoms
D) become infected, but the sap from these plants would be unable to infect other plants

Answer: B

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32) Which of the following can be effective in preventing the onset of viral infection in humans?

A) taking vitamins
B) getting vaccinated
C) taking antibiotics

D) taking drugs that inhibit transcription

Answer: B

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33) Viral infections in plants _____.
A) can be controlled with antibiotics
B) can spread within a plant via plasmodesmata C) have little effect on plant growth
D) are not spread by animals

Answer: B

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34) Which of the following represents a difference between viruses and viroids?
A) Viruses infect many types of cells, whereas viroids infect only prokaryotic cells.
B) Viruses have capsids composed of protein, whereas viroids have no capsids.
C) Viruses have genomes composed of RNA, whereas viroids have genomes composed of DNA.

D) Viruses cannot pass through plasmodesmata, whereas viroids can.

Answer: B

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35) The difference between vertical and horizontal transmission of plant viruses is that vertical transmission is _____.
A) transmission of a virus from a parent plant to its progeny, and horizontal transmission is one plant spreading the virus to another plant

B) the spread of viruses from upper leaves to lower leaves of the plant, and horizontal transmission is the spread of a virus among leaves at the same general level
C) 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

D) 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

Answer: A

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36) What are prions?
A) mobile segments of DNA
B) tiny circular molecules of RNA that can infect plants
C) viral DNA that attaches itself to the host genome and causes disease

D) misfolded versions of normal protein that can cause disease

Answer: D

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37) A person is most likely to recover from a viral infection if the infected cells _____.

A) can undergo normal cell division
B) can carry on translation, at least for a few hours
C) produce and release viral protein

D) transcribe viral mRNA

Answer: A

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38) Effective antiviral drugs are usually associated with which of the following properties?

A) interference with viral replication
B) prevention of the host from becoming infected
C) removal of viral proteins

D) removal of viral mRNAs

Answer: A

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39) Which of the following 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) A flu virus from a human epidemic or pandemic infects birds; the birds replicate the virus differently and then pass it back to humans.
C) 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.

D) An animal such as a pig is infected with more than one virus, genetic recombination occurs, the new virus mutates, the virus is passed to a new species such as a bird, and the virus mutates again and can now be transmitted to humans.

Answer: D

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You isolate an infectious substance 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 to analyze the substance and determine the nature of the infectious agent.

I. Treat the substance with enzymes that destroy all nucleic acids and then determine whether the substance is still infectious.
II. Filterthesubstancetoremoveallelementssmallerthanwhatcanbeeasilyseenunderalight microscope.

III. Culture the substance on nutritive medium, away from any plant cells.
IV. Treat the sample with proteases that digest all proteins and then determining whether the substance is still infectious.

40) If you already know that the infectious agent was either bacterial or viral, which method(s) listed above would allow you to distinguish between these two possibilities?
A) I
B) II

C) II or III
D) IV

Answer: C

35

You isolate an infectious substance 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 to analyze the substance and determine the nature of the infectious agent.

I. Treat the substance with enzymes that destroy all nucleic acids and then determine whether the substance is still infectious.
II. Filterthesubstancetoremoveallelementssmallerthanwhatcanbeeasilyseenunderalight microscope.

III. Culture the substance on nutritive medium, away from any plant cells.
IV. Treat the sample with proteases that digest all proteins and then determining whether the substance is still infectious.

41) If you already know that the infectious agent was either a viroid or a prion, which method(s) listed above would allow you to distinguish between these two possibilities?
A) I only
B) II only

C) IV only
D) either I or IV

Answer: D

36

The herpes viruses are important enveloped DNA viruses that cause disease in vertebrates and in some invertebrates such as oysters. Some of the human forms 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 later reactivate, replicate again, and infect others.

42) 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) vaccinate of all persons with preexisting cases of HSV
B) interfere with new viral replication in preexisting cases of HSV
C) treat HSV lesions to shorten the breakout
D) educate people about avoiding sources of infection

Answer: B

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43) What is difference between an epidemic and a pandemic?
A) An epidemic is a disease; a pandemic is a treatment.
B) An epidemic is restricted to a local region; a pandemic is global.
C) An epidemic has low mortality; a pandemic has higher mortality.
D) An epidemic is caused by a bacterial infection; a pandemic is caused by a viral infection.

Answer: B

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44) Will treating a viral infection with antibiotics affect the course of the infection?
A) No; antibiotics work by inhibiting enzymes specific to bacteria. Antibiotics have no effect on eukaryotic or virally encoded enzymes.
B) No; antibiotics do not kill viruses because viruses do not have DNA or RNA.
C) Yes; antibiotics activate the immune system, and this decreases the severity of the infection. D) Yes; antibiotics can prevent viral entry into the cell by binding to host-receptor proteins.

Answer: A

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45) Why do scientists consider HIV to be an emerging virus?
A) HIV infected humans long before the 1980s, but it has now mutated to a more deadly form.

B) HIV mutates rapidly making the virus very different from HIV in the early 1980s.
C) HIV suddenly became apparent and widespread in the 1980s.
D) HIV is now starting to cause diseases other than AIDS, such as rare types of cancers and pneumonias.

Answer: C

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46) A population of viruses with similar characteristics is called a _____.

A) strain
B) species
C) type

D) genome

Answer: A

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47) Evidence suggests that factors which contribute towards the virulence of E. coli strain O157:H7, a bacterial strain reported to cause several food poisoning deaths, are caused by genes from a virus that infects bacteria. Considering this evidence, which statement most likely explains how the O157:H7 population acquired the genetic variation that distinguishes the strain from harmless E. coli strains, such as those that reside in our intestines?
A) The virus entered the bacterial cell and incorporated its DNA into the bacterial genome, allowing the bacteria’s cellular machinery to create new viruses.
B) Viral envelope proteins bind to receptors on the bacterial membrane, allowing the viral genetic material to enter the bacterium and become translated into proteins.
C) The virus entered the cell and acquired specific genes from the bacteria to increase the virulence of the virus.
D) The virus infected the bacterium, and allowed the bacterial population to replicate with a copy of the phage genome in each new bacterium.

Answer: D

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48) Which of the following processes within viral replication is the greatest source of genetic variation in RNA virus populations?
A) High mutation rate due to lack of proofreading of RNA genome replication errors.
B) Transcription from the host cell RNA polymerase introduces numerous mutations.

C) Capsid proteins from the host cell can replace the viral capsid.

D) Viral RNA is translated by host cell ribosomes.

Answer: A

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49) In 2009, a flu pandemic was believed to have originated when viral transmission occurred from pig to human, thereby earning the designation, "swine flu." Although pigs are thought to have been the breeding ground for the 2009 virus, sequences from bird, pig, and human viruses were all found within this newly identified virus. What is the most likely explanation of why this virus contained sequences from bird, pig, and human viruses?

A) The virus was descended from a common ancestor of bird, pig, and human flu viruses.

B) The infected individuals happened to be infected with all three virus types.
C) Related viruses can undergo genetic recombination if the RNA genomes mix and match during viral assembly.

D) The human was likely infected with various bacterial strains that contained all three RNA viruses.

Answer: C