Chapter 19

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1) What characteristics of electron microscopes make them most useful for studying viruses?
A) high energy electrons with high penetrance
B) requirement that specimens be viewed in a vacuum
C) necessity for specimens to be dry and fixed
qE) use of magnetic fields to focus electrons

D) shorter wavelengths providing higher resolution

2) Viral genomes vary greatly in size and may include from four genes to several hundred genes.
Which of the following viral features is most apt to correlate with the size of the genome?
A) size of the viral capsomeres
B) RNA versus DNA genome
C) double versus single strand genomes
D) size and shape of the capsid
E) glycoproteins of the envelope

D) size and shape of the capsid

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

B) antibodies against specific proteins not found in the host membranes

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

A) the proteins on its surface and that of the host.

5) Why are viruses referred to as obligate parasites?
A) They cannot reproduce outside of a host cell.
B) Viral DNA always inserts itself into host DNA.
C) They invariably kill any cell they infect.
D) They can incorporate nucleic acids from other viruses.
E) They must use enzymes encoded by the virus itself.

A) They cannot reproduce outside of a host cell

6) Which of the following molecules make up the viral envelope?
A) glycoproteins
B) proteosugars
C) carbopeptides
D) peptidocarbs
E) carboproteins

A) glycoproteins

7) Most human-infecting viruses are maintained in the human population only. However, a
zoonosis is a disease that is transmitted from other vertebrates to humans, at least sporadically,
without requiring viral mutation. Which of the following is the best example of a zoonosis?
A) rabies
B) herpesvirus
C) smallpox
D) HIV
E) hepatitis virus

A) rabies

Use the following information to answer the following questions.
In 1971, David Baltimore described a scheme for classifying viruses based on how the virus
produces mRNA.
The table below shows the results of testing five viruses for nuclease specificity, the ability of
the virus to act as an mRNA, and presence (+) or absence (-) of its own viral polymerase.
Virus Nuclease Sensitivity Genome as mRNA Polymerase
A Dnase - -
B Rnase + -
C Dnase - +
D Rnase - +
E Rnase + -
8) Given Baltimore's scheme, a positive sense single-stranded RNA virus such as the polio virus
would be most closely related to which of the following?
A) T-series bacteriophages
B) retroviruses that require a DNA intermediate
C) single-stranded DNA viruses such as herpesviruses
D) nonenveloped double-stranded RNA viruses
E) linear double-stranded DNA viruses such as adenovirus

B) retroviruses that require a DNA intermediate

9) Based on the above table, which virus meets the Baltimore requirements for a retrovirus?

D

10) Based on the above table, which virus meets the requirements for a bacteriophage?

A

11) A linear piece of viral DNA of 8 kb can be cut with either of two restriction enzymes (X and
Y). These are subjected to electrophoresis and produce the following bands:
Cutting the same 8 kb piece with both enzymes together results in bands at 4.0, 2.5, 1.0, and 0.5.
Of the possible arrangements of the sites given below, which one is most likely?

B

12) 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 life?
A) re-infection by a closely related herpesvirus of a different strain
B) re-infection by the same herpesvirus strain
C) co-infection with an unrelated virus that causes the same symptoms
D) copies of the herpesvirus genome permanently maintained in host nuclei
E) copies of the herpesvirus genome permanently maintained in host cell cytoplasm

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

13) 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) 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
E) utilization of eukaryotic polymerases

C) control of more than one gene in an operon

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

D) A large number of phages is released at a time.

15) Which of the following terms describes bacteriophage DNA that has become integrated into
the host cell chromosome?
A) intemperate bacteriophages
B) transposons
C) prophages
D) T-even phages
E) plasmids

C) prophages

16) Which of the following statements describes the lysogenic cycle of lambda (_) 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) 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.

C) The phage genome replicates along with the host genome

17) 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 the proofreading steps of DNA replication.
C) RNA viruses replicate faster.
D) RNA viruses can incorporate a variety of nonstandard bases.
E) RNA viruses are more sensitive to mutagens.

B) Replication of their genomes does not involve the proofreading steps of DNA replication.

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

E) Viral genomes are usually more similar to the genome of the host cell than to the genomes of
viruses that infect other cell types.

19) 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 some but not all of the symptoms of the TMV infection.
B) The plants would develop symptoms typically produced by viroids.
C) The plants would develop the typical symptoms of TMV infection.
D) The plants would not show any disease symptoms.
E) The plants would become infected, but the sap from these plants would be unable to infect
other plants.

C) The plants would develop the typical symptoms of TMV infection.

20) What is the name given to viruses that are single-stranded RNA that acts as a template for
DNA synthesis?
A) retroviruses
B) proviruses
C) viroids
D) bacteriophages
E) lytic phages

A) retroviruses

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

B) It uses viral RNA as a template for DNA synthesis.

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

A) getting vaccinated

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
23) Which treatment could definitively determine whether or not the component is a viroid?
A) I
B) II
C) III
D) IV
E) first II and then III

A) I

24) 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) I
B) II
C) III
D) IV
E) either II or IV

C) III

25) Which treatment would you use to determine if the agent is a prion?
A) I only
B) II only
C) III only
D) IV only
E) either I or IV

D) IV only

26) Which of the following describes plant virus infections?
A) They can be controlled by the use of antibiotics.
B) They are spread throughout a plant by passing through the plasmodesmata.
C) They have little effect on plant growth.
D) They are seldom spread by insects.
E) They can never be inherited from a parent.

B) They are spread throughout a plant by passing through the plasmodesmata.

27) 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 contain introns; viroids have only exons.
D) Viruses always have genomes composed of DNA, whereas viroids always have genomes
composed of RNA.
E) Viruses cannot pass through plasmodesmata; viroids can.

B) Viruses have capsids composed of protein, whereas viroids have no capsids

28) The difference between vertical and horizontal transmission of plant viruses is that
A) 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.
B) vertical transmission is 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.

A) 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.

29) What are prions?
A) misfolded versions of normal brain protein
B) tiny molecules of RNA that infect plants
C) viral DNA that has had to attach itself to the host genome
D) viruses that invade bacteria
E) a mobile segment of DNA

A) misfolded versions of normal brain protein

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

A) ability of the infected cell to undergo normal cell division

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

B) interference with the viral reproduction

32) Which of the following series best reflects what we know about how the flu virus moves
between species?
A) 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) The flu virus in a pig is mutated and replicated in alternate arrangements so that humans who
eat the pig products can be infected.
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 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, the virus mutates and can be transmitted to humans.

E) 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, the virus mutates and can be transmitted to humans.

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

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