Complete Test Bank Chapter 13 Viruses, Viroids, And Prions

Nester’s Microbiology, 9e (Anderson)

Chapter 13 Viruses, Viroids, and Prions

1) Viruses that infect bacteria are referred to as

A) viralcidens.

B) bacteriocidins.

C) bacterialogens.

D) bacteriophages.

E) virophages.

2) A virion is a(n)

A) pathogenic virus.

B) subviral particle.

C) complete, extracellular virus particle.

D) enveloped virus particle.

E) non-enveloped virus particle.

3) A virion is composed of

A) lipid, protein, and either RNA or DNA.

B) protein, either RNA or DNA, and possibly lipid.

C) protein and either RNA or DNA, but no lipid.

D) protein and both RNA and DNA, but no lipid.

E) protein, and possibly lipid.

4) Which of the following BEST describes the protein coat of a virus? It

A) is called a capsomere, AND is involved in the recognition of host cell receptors by non-enveloped viruses.

B) is called a capsid, AND is involved in the recognition of host cell receptors by non-enveloped viruses.

C) protects the nucleic acid, AND is involved in the recognition of host cell receptors by non-enveloped viruses.

D) is called a capsomere, protects the nucleic acid, AND is involved in the recognition of host cell receptors by non-enveloped viruses.

E) is called a capsid, protects the nucleic acid, AND is involved in the recognition of host cell receptors by non-enveloped viruses.

5) Which does not refer to the shape of a virus?

A) Bacillus

B) Icosahedral

C) Helical

D) Complex

E) These are all virus shapes.

6) The shape of the virus is determined by its

A) nucleic acid.

B) capsid.

C) envelope.

D) tail.

E) spikes.

7) The viral envelope closely resembles the

A) prokaryotic cell wall.

B) capsomere.

C) eukaryotic cytoplasmic membrane.

D) cytoplasm.

E) eukaryotic cell wall.

8) The protein projections on the surface of a virus that are involved in attachment to the host cell are called

A) suckers.

B) pili.

C) cilia.

D) spikes.

E) hooks.

9) Outside of living cells, viruses are

A) scavenging glucose.

B) gaining ATP from the mitochondria.

C) metabolically inert.

D) using cilia to move to the next host.

E) replicating by binary fission.

10) What part of the attached bacteriophage enters through the host cell wall?

A) The entire virus.

B) Only the enzymes necessary for replication.

C) The nucleic acid.

D) The nucleic acid and capsid.

E) The capsid only.

11) A phage that replicates inside the host cell and then lyses its host during its release is a

A) virulent or lytic phage.

B) latent phage.

C) lysogenic phage.

D) dormant phage.

E) temperate phage.

12) The correct order for the stages of a phage infection is

A) penetration, transcription, attachment, replication of nucleic acid and protein, assembly, release.

B) attachment, penetration, transcription, replication of nucleic acid and protein, assembly, release.

C) attachment, replication of nucleic acid and protein, penetration, transcription, assembly, release.

D) transcription, attachment, replication of nucleic acid and protein, assembly, penetration, release.

E) attachment, replication of nucleic acid and protein, assembly, penetration, transcription, release.

13) Phages that can either replicate and cause cell lysis or can integrate their DNA into the host DNA are called

A) temperate phages.

B) lytic phages.

C) virulent phages.

D) segmented phages.

E) bacteriophages.

14) One of the most intensively studied virulent phages which infects E. coli is ________.

A) T9

B) T4

C) beta

D) gamma

E) lambda

15) During attachment of phage to E. coli, the phage

A) actively seeks out the bacteria AND attaches to proteins or carbohydrates on the bacterial surface.

B) randomly bumps into the bacteria AND attaches to proteins or carbohydrates on the bacterial surface.

C) randomly bumps into the bacteria AND attaches to the bacterial RNA.

D) randomly bumps into the bacteria AND attaches to the bacterial DNA.

E) actively seeks out the bacteria AND attaches to the bacterial DNA.

16) What part of the E. coli T4 phage attaches to the host cell receptors?

A) Capsid fragments around the nucleic acid.

B) Protein fibers at the end of the phage tail.

C) Pili of the envelope.

D) Spikes of the envelope.

E) Spikes of the cell wall.

17) During penetration of E. coli by the T4 phage,

A) lysozyme is used to allow entry of the phage capsid.

B) the tail acts as a "hypodermic needle," injecting the phage DNA into the cell.

C) the protein fibers digest a hole in the cell wall.

D) the bacterial receptor molecules open a hole through the cell wall.

E) the intact phage enters the host by endocytosis.

18) Phage-encoded proteins are

A) coded for by host DNA.

B) coded for by phage DNA.

C) proteins normally present in the uninfected cell.

D) early proteins.

E) coded for by phage DNA AND early proteins.

19) Phage-encoded enzymes are

A) all produced simultaneously AND are used to customize the cell for viral production.

B) produced in a sequential manner AND are used to destroy the host cell.

C) are strictly host enzymes AND are used to customize the cell for viral production.

D) produced in a sequential manner AND are used to customize the cell for viral production.

E) all produced simultaneously AND are used to destroy the host cell.

20) Assembly of the T4 phage

A) is completely self-assembly 

B) is completely dependent on scaffolds.

C) may involve some self-assembly AND may involve the use of scaffolds.

D) may involve some self-assembly AND is completely dependent on scaffolds.

E) is completely self-assembly AND is never dependent on scaffolds.

21) In the case of T-even phages, the burst size is about

A) 1 per host cell.

B) 5 per host cell.

C) 20 per host cell.

D) 200 per host cell.

E) 1,000 per host cell.

22) The time from absorption to release for T-even phage is about

A) 1 day.

B) 30 minutes.

C) 10 minutes.

D) 1 minute.

E) 45 seconds.

23) The replicative form of nucleic acid in filamentous phages is

A) dsDNA.

B) dsRNA.

C) positive ssRNA.

D) negative ssDNA.

E) positive ssDNA.

24) Filamentous phages

A) only infect E. coli that have pili.

B) only infect E. coli lacking pili.

C) infect E. coli regardless of the presence of pili.

D) do not infect E. coli.

E) only infect Gram-negative E. coli.

25) Which is a filamentous phage?

A) M13

B) T4

C) Lambda

D) TMV

E) T2

26) The bacterial viruses that are released by a process termed extrusion are called

A) lysogenic viruses.

B) temperate phages.

C) filamentous phages.

D) lambda viruses.

E) helical phages.

27) The filamentous phages all contain

A) single-stranded DNA.

B) double-stranded DNA.

C) single-stranded RNA.

D) double-stranded RNA.

E) single-stranded RNA, OR single-stranded DNA.

28) An exit method used by viruses that does not immediately destroy the host bacterium is

A) lysis.

B) inversion.

C) extrusion.

D) excising.

E) endocytosis.

29) In the replication of phage containing positive-sense DNA,

A) the host's enzymes are used to make dsDNA.

B) the host's DNA polymerase uses the phage RNA as a template to make negative-sense DNA.

C) a phage-encoded DNA polymerase is used to make negative-sense RNA using the phage positive-sense RNA as a template.

D) a phage-encoded DNA polymerase is used to make DNA using the phage positive-sense RNA as a template.

E) a phage-encoded RNA polymerase is used to make DNA using the phage positive-sense RNA as a template.

30) Which statement about most phages that contain single-stranded DNA is NOT true?

A) They are extruded from the host cell.

B) They contain a negative-sense DNA strand.

C) Their DNA is transformed to dsDNA before replication and transcription occur.

D) All of the choices are correct.

E) None of the choices is correct.

31) Which statement regarding phage replication is TRUE?

A) A lysogen is a bacterial cell with an integrated prophage.

B) When integrated into host DNA, phage DNA is called a virophage.

C) Lambda is a good example of a lytic phage.

D) Lambda can be a lytic or a temperate phage.

E) A lysogen is a virus that has bacterial DNA in it.

32) A temperate phage

A) may be lysogenic.

B) may be lytic.

C) enters a lysogenic or lytic life cycle shortly after entering the host cell.

D) may be lytic AND enters a lysogenic or lytic life cycle shortly after entering the host cell.

E) may be lysogenic AND enters a lysogenic or lytic life cycle shortly after entering the host cell.

33) The integration of phage DNA into the bacterial chromosome occurs because of

A) the phage's ability to synthesize an enzyme that integrates its DNA into the host's chromosome.

B) the phage's ability to synthesize enzymes that allow it to enter the bacterium.

C) similarity in RNA nucleotides in both the phage and the bacterial host.

D) the similarity in enzyme metabolism in the phage and the bacterial cell.

E) the phage's ability to synthesize enzymes to enter the bacterium AND similar RNA nucleotides in both.

34) Once integrated, phage DNA can remain in the prophage state as long as

A) the bacteria is frequently plated on new media.

B) certain phage genes are excised.

C) certain phage genes are repressed.

D) bacterial repressor genes are activated.

E) bacterial repressor genes are deactivated.

35) The activation of the SOS system in a bacterium infected with a prophage results in

A) destruction of certain bacterial genes AND destruction of the viral repressor through host protease activity.

B) destruction of the viral repressor through host protease activity AND complete lysis of the bacterial culture.

C) destruction of the viral repressor through host protease activity AND mutation of the DNA 

D) complete lysis of the bacterial culture, destruction of the viral genes, AND mutation of the DNA.

E) destruction of certain bacterial genes AND complete lysis of the bacterial culture.

36) Which is true of lysogenized cells?

A) They are immune to any further infection by any virus.

B) They are immune to infection by the same virus.

C) They may have new properties AND they respond to infection with the SOS response.

D) They respond to infection with the SOS response.

E) They are immune to infection by the same virus AND may have new properties.

37) The phenomenon responsible for the ability of Corynebacterium diphtherium to produce the virulent toxin responsible for the devastating effects of diphtheria is called

A) self-assembly.

B) matrix conversion.

C) lysogenic conversion.

D) prion protein.

E) phase variation.

38) Transducing virulent phages do not lyse the cells they invade because

A) transformation is taking place in the phage and this is transferred to the bacterium.

B) bacterial DNA has replaced critical viral DNA in the phage.

C) their virulence is dependent on the bacteria and virus replicating together.

D) the lytic genes are unable to enter during penetration and are shed outside the host.

E) viral DNA has replaced critical bacterial DNA in the phage.

39) A limiting factor for viral infection of animals cells is

A) presence of specific receptor molecules on the host cell.

B) internal metabolic temperature of the host cell.

C) nutrition of the host cell.

D) stage of cell cycle of the host cell.

E) culture conditions of the host cell.

40) If the infecting phage lacks some critical pieces of DNA necessary for replication, it is called

A) incomplete.

B) mutated.

C) defective.

D) vegetative.

E) carcinogenic.

41) All of the statements about specialized transduction are correct EXCEPT

A) it involves the random transmission of any gene.

B) it involves the transfer of a few specific genes.

C) it involves a defective virus.

D) it only involves genes near the viral DNA integration site.

E) it involves temperate phages.

42) Once inside the host cell, phage DNA

A) is replicated.

B) is transcribed.

C) may get degraded by bacterial nucleases.

D) may integrate into the host chromosome.

E) All of the choices are correct.

43) Using phages to treat a bacterial infection is an interesting idea because

A) a single type of phage can destroy a wide range of strains of the same pathogen.

B) of the increasing problem of antibiotic resistance in pathogens.

C) lysed bacteria pose no threat to a person's health.

D) a single phage can be genetically engineered to infect many different species of bacteria.

E) of the increasing problem of antibiotic resistance in people.

44) A lysogenic cell contains viral DNA (a prophage) integrated into the host chromosome.

45) The integration of phage DNA into host DNA occurs in much the same fashion as seen in transformation, transduction, or conjugation.

46) What are two ways that phage can replicate without directly lysing their host cell?

A) Conjugation and lysogeny

B) Lysogeny and transduction

C) Extrusion and transformation

D) Extrusion and lysogeny

E) Extrusion and lysis

47) What is a defective phage?

A) A virus that has lost some of its genetic material, and therefore cannot infect a new target cell.

B) A virus that has lost some of its genetic material, and therefore cannot replicate within a new target cell.

C) A virus that lacks the ability to replicate independently of its host cell and cannot survive.

D) A virus that cannot attach to its host cell and therefore cannot enter the target cell.

E) A virus that lacks a prophage, cannot enter a host cell, and cannot survive.

48) A filamentous phage is incapable of causing a lytic infection.

49) Completed filamentous phages are often found in the cytoplasm of infected bacteria.

50) Virulent as well as temperate phages can serve as generalized transducing phages.

51) Transduction often involves defective virus.

52) The host range of a virus depends on the presence of host receptor molecules.

53) The nucleocapsid is composed of

A) DNA and RNA and protein.

B) DNA or RNA, and protein.

C) protein located in the nucleus.

D) nucleic acid in the ribosome.

E) DNA or RNA, lipid, and protein.

54) Enveloped viruses

A) never use spikes for attachment to host cells.

B) have a lipid bilayer membrane containing various proteins.

C) are surrounded by an additional layer of carbohydrate.

D) surround the boundary of a host cell.

E) are difficult to destroy using detergents.

55) The term "segmented" refers to viruses that

A) may contain several pieces of RNA.

B) have an icosahedral-shaped capsid.

C) are linked together before budding out.

D) have an envelope that has several components.

E) may contain RNA with undefined regions in it.

56) The terms helical, icosahedral, and complex refer to

A) viral life cycles.

B) forms of nucleic acid.

C) types of viral envelopes.

D) shapes of viruses.

E) types of bacteriophages.

57) Animal viruses are divided into a number of families whose names end in

A) -virus.

B) -viridae.

C) -viscous.

D) -eieio.

E) -virum.

58) There are ________ major families of DNA-containing viruses that infect vertebrates.

A) 7

B) 5

C) 4

D) 2

E) 6

59) There are ________ major families of RNA containing viruses that infect vertebrates.

A) 2

B) 5

C) 7

D) 13

E) 6

60) Viruses are commonly referred to by their ________ name.

A) locale AND genus

B) genus AND species

C) disease AND species

D) disease AND locale

E) disease AND genus

61) The common species name of the virus is frequently based on the

A) presence or absence of a nuclear membrane.

B) type of nucleic acid it contains.

C) disease the virus causes.

D) geographic area it is found.

E) shape of the viral nucleocapsid.

62) The family to which the Rhinovirus belongs is the

A) Picornaviridae.

B) Enterovirus.

C) Enteroviridae.

D) Picornavirus.

E) Rhinoviridae.

63) A key feature of all viral infections is the

A) integration of viral DNA into host DNA.

B) separation of viral nucleic acid from the capsid.

C) disintegration of host DNA.

D) addition of a lipid membrane to the virus.

E) lysis of the host cell.

64) An infection in which the virus is continually present in the body is referred to as

A) acute.

B) balanced.

C) determinant.

D) persistent.

E) fatal.

65) Attachment of animal viruses to the host cell may be by means of

A) a tail.

B) the envelope.

C) spikes.

D) a capsid.

E) a membrane.

66) The receptors to which animal virus attachment proteins usually bind are

A) glycoproteins.

B) proteins.

C) carbohydrates.

D) nucleic acid.

E) lipids.

67) Resistance of some animals to certain viral diseases is based on

A) lack of spikes for attachment.

B) lack of specific receptors on the host cell.

C) phagocytosis of the virus by the host cell.

D) the presence of the viral envelope.

E) immunity in the host cell.

68) When a non-enveloped animal virus adsorbs to the host cell with its protein spikes, the virions are taken into the cell by the process of

A) penetration.

B) production.

C) endocytosis.

D) fusion.

E) budding.

69) Entry of bacteriophages and animal viruses into host cells

A) is by endocytosis.

B) is by fusion.

C) involve entry of the entire nucleocapsid.

D) differs because bacteriophages leave the capsid outside the cell, while animal virus entry involves the entry of the whole nucleocapsid.

E) differs because animal viruses leave the capsid outside the cell, while bacteriophage entry involves the entry of the whole nucleocapsid.

70) For which of the following processes are enzymes not required?

A) Replication

B) Self-assembly

C) Translation

D) Maturation

E) All of the answer choices are correct.

71) Cells infected with animal viruses lyse because

A) the release of the virions depletes the cell of energy.

B) the virus releases enzymes that lyse the cell.

C) functions necessary for cell survival are not carried out and the cell dies.

D) the virus RNA and cellular protein interact to kill the cell.

E) the viruses release lysozyme which destroys the host cell wall.

72) In addition to lysis, animal viruses may exit the host cell by

A) extrusion.

B) budding.

C) fission.

D) fusion.

E) endocytosis.

73) In the region of budding, the inside of the cytoplasmic membrane becomes coated with

A) enzymes.

B) carbohydrates.

C) steroids.

D) matrix proteins.

E) phospholipids.

74) In the region of budding, the cytoplasmic membrane acquires

A) carbohydrates AND spike proteins.

B) spike proteins AND enzymes.

C) spike proteins AND matrix proteins.

D) matrix proteins AND carbohydrates.

E) enzymes AND matrix proteins.

75) The enveloped viruses typically obtain their envelope

A) from the host cytoplasmic membrane as they exit the host.

B) from a newly constructed viral-derived membrane.

C) from the nuclear membrane as they exit the host.

D) from endoplasmic reticulum in the host.

E) from the host peptidoglycan as they exit.

76) Carriers

A) may have a persistent infection.

B) may be a source of infection.

C) usually show symptoms of the disease AND may be a source of infection.

D) have been cured of the infection.

E) may have a persistent infection AND may be a source of infection.

77) In latent infections, the virions are

A) constantly produced.

B) only produced during reactivation.

C) produced very slowly.

D) continually being slowly budded out.

E) always detectable in the infected person.

78) The best known chronic infection involves

A) hepatitis B.

B) hepatitis A.

C) chickenpox.

D) herpes.

E) influenza.

79) The genome of retroviruses is made of

A) ssDNA.

B) dsDNA.

C) ssRNA.

D) dsRNA.

E) protein and RNA.

80) The best-known examples of viruses that cause latent infections are

A) polio AND herpes.

B) herpes AND measles.

C) measles AND chickenpox.

D) chickenpox AND polio.

E) herpes AND chickenpox.

81) Diseases of short duration frequently followed by long-term immunity are referred to as

A) intermittent infections.

B) chronic infections.

C) acute infections.

D) persistent infections.

E) nonacute infections.

82) Retroviruses are unique in that they

A) replicate in nervous system cells.

B) use RNA as a template to make DNA.

C) do not have a capsid.

D) use DNA as a template to make RNA.

E) use RNA as a template to make more RNA.

83) Genetic exchange in segmented viruses that allows a zoonotic virus to infect humans is an example

A) antigenic shift.

B) hemagglutination.

C) genetic reassortment.

D) antigenic drift.

E) mutagenesis.

84) Which statement(s) about cells taken from a tumor is/are true?

A) They may be used to grow viruses.

B) They may be used to grow bacteriophages.

C) They divide 50 times and then die.

D) They may be used to grow viruses AND they may be used to grow bacteriophages.

E) They divide 50 times and then die AND they may be used to grow bacteriophages.

85) Viruses are not cultivated in

A) live organisms.

B) embryonated chicken eggs.

C) tissue culture.

D) blood agar.

E) plants.

86) The changes that occur in virally infected cells are characteristic for a particular virus and are referred to as the

A) cytopathic effect.

B) phenotypic effect.

C) genotypic expression.

D) cytology.

E) symptomatic effect.

87) Normal tissue taken from animals and prepared immediately as a medium for viral growth is termed a(n)

A) advantageous group.

B) monolayer culture.

C) primary culture.

D) plaque.

E) virus culture.

88) If reasonably pure preparations of virus are available, the number of virus present may be determined by

A) photocolorimetry.

B) electron microscopy.

C) gas chromatography.

D) light microscopy.

E) spectrophotometry.

89) The approximate viral concentration of a sample may be determined by

A) quantal assay.

B) endpoint assay.

C) the titer.

D) the lysate assay.

E) cytopathic assay.

90) The concentration of virus that infects or kills 50% of the host cells is referred to as the

A) LD50

B) ID50

C) ID100

D) LD100 AND ID100

E) LD50 AND ID50

91) One group of animal viruses that are able to agglutinate red blood cells are the

A) coronaviruses.

B) orthomyxoviruses.

C) retroviruses.

D) reoviruses.

E) rhinoviruses.

92) The site at which a virus has infected and subsequently lysed the infected cell, releasing its progeny to infect and lyse surrounding cells, thereby forming a "clear zone," is

A) a burst area.

B) a lyse area.

C) a plaque.

D) a dead zone.

E) a zone of inhibition.

93) Which of the following is not a characteristic of normal cells?

A) They grow as a monolayer.

B) They grow as multiple layers.

C) They undergo a limited number of divisions and then die.

D) They stick tightly to the surface of glass culture dishes.

E) These are all characteristics of normal cells.

94) Plant viruses enter the host plant via

A) wound sites.

B) specific receptors.

C) nonspecific receptors.

D) seeds.

E) endocytosis.

95) Plant viruses may be transmitted by

A) worms.

B) contaminated seeds.

C) humans.

D) insects.

E) All of the choices are correct.

96) Which of the following is NOT true of prions?

A) Prions replicate by converting normal host prion proteins into abnormal prion proteins.

B) Prions responsible for "mad cow disease" can cause a similar disease in humans.

C) Prions can be transmitted by consumption of dried food or cooked food.

D) Prions that cause spongiform encephalopathies have a different amino acid sequence from PrPc.

E) All of the answer choices are correct.

97) Prions

A) consist of a special nucleocapsid.

B) are made of protein only.

C) are made of RNA only.

D) are made of dsRNA and protein.

E) consist of proteins and phospholipids.

98) Prions affect the

A) respiratory system.

B) gastrointestinal tract.

C) nervous system.

D) lymphatic system.

E) urogenital system.

99) Viroids characteristically are composed of

A) ssRNA.

B) dsRNA.

C) ssDNA.

D) dsDNA.

E) protein only.

100) Viroids cause disease in

A) animals.

B) plants.

C) bacteria.

D) fungi.

E) plants and fungi.

101) Prions are

A) a form of RNA virus.

B) a form of DNA virus.

C) a viroid.

D) an infectious protein.

E) an infected protein.

102) Spongiform encephalopathy occurs in all of the following EXCEPT

A) plants.

B) humans.

C) cattle.

D) sheep.

E) cattle AND sheep.

103) Bacteriophages, unlike animal viruses, often have special viral-specific enzymes carried in the capsid, which enter the host cell at the same time as the nucleic acid.

104) The structure of plant, animal, and bacterial viruses are each, fundamentally, very different from one another.

105) Capsids are made of a number of capsomeres that are covalently bonded to one another.

106) Non-enveloped and enveloped viruses both may enter the host via endocytosis.

107) All viruses must separate the nucleic acid from the capsid before replication.

108) If a virus utilizes a lytic life cycle of reproduction, it will not induce tumors.

109) Viruses that cause acute infection result in productive infections.

110) Electron microscopy is useful for counting viruses and distinguishing between infective and non-infective virions.

111) Infective and non-infective viruses may be distinguished by growth on MacConkey's agar.

112) An antibiotic is added to a culture of E. coli, resulting in death of the cells. Bacteriophages are then added. Would the phages replicate in the E. coli cells? Why or why not?

A) Yes, because the cellular machinery of the bacteria is most likely still active. The bacteriophages could use that machinery to replicate new virus particles.

B) No, because the bacteriophages would depend too much on having the active machinery of a living host cell for replication. 

C) Yes, because bacteriophages are capable of reanimating dead cells to force them to produce more virus particles.

D) No, because entry of the bacteriophages into the target cell is dependent on the cell being alive to conduct endocytosis of the virus.

E) No, because dead E. coli cells do not have any receptors on their cell walls to which the bacteriophages can attach for entry into the host cell by fusion.

113) Most temperate phages integrate into the host chromosome, whereas some replicate as plasmids. Which kind of relationship do you think would be more likely to maintain the phage in the host cell, and why?

A) Plasmids; they're smaller, so they would be easier to replicate by the host cell.

B) Integrated; the host cell would be less likely to view this DNA as "foreign" on subsequent rounds of replication, and would retain it more easily.

C) Plasmids; these structures often carry other genes that may give the host cell a selective advantage over cells that don't have them.

D) Integration, because plasmids are frequently lost during cell division, which could leave a daughter cell without the virus genome.

E) Either plasmids or integration because once a virus genome is in a host cell, there is not way for that genome to be removed from the infected cell.

114) You add an unknown phage to a mixture of F+ and F− cells of E. coli and plate out the bacteria. The bacterial colonies that grow are all F−. How can you explain this phenomenon?

A) The phage bound to a receptor on the sex pilus, and therefore only infected the F+ cells (leaving the F− cells alone).

B) The phage bound to a receptor on the F− cells, leaving only them alive and allowing the F+ cells to die off.

C) The phage integrated (lysogenized) the F− cells, giving them a selective advantage over the F+ cells.

D) F+ cells are uniquely susceptible to phage attack for unknown reasons.

E) F+ are well known to die in the presence of any type of bacteriophage.

115) Why do animal viruses have envelopes and phages rarely do?

A) Since bacteria don't have cell membranes, the bacterial viruses (phages) don't pick them up when they leave the target cells.

B) Phages acquire an outer surrounding that is a part of the cell wall of the bacterium they were created in, rather than an outer surrounding of plasma membrane.

C) Animal viruses will often use the envelope in order to fuse with the plasma membrane of a new target cell, gaining entry into the cytoplasm.

D) Animal viruses build the envelope inside of the target cell as they are being replicated, but before the cell breaks open and releases them into the extracellular environment. The envelope is a remnant of this building process.

E) This is a trick question. Plenty of bacteriophages have envelopes that they acquire when they bud through the lipopolysaccharide layer of the bacterial host.

116) Explain why HIV becomes resistant so quickly when a single drug is used therapeutically.

A) The virus is an RNA genome virus. By using host RNA polymerase to directly copy the genome to make more virus particles, there's no proofreading capability. This leads to a high rate of mutation of the viral genome and increased chance for drug resistance.

B) HIV uses reverse transcriptase to make a cDNA version of its RNA genome. This polymerase is "'sloppy," with a high rate of error and lack of a proofreading capability. This leads to a high rate of mutation of the viral genome and increased chance for drug resistance.

C) HIV synthesizes a protein enzyme that directly cleaves anti-HIV drugs, giving it a characteristically high rate of resistance to a single drug type.

D) HIV is constantly changing its genetic structure by swapping genetic elements with other virus strains. This leads to a high rate of mutation of the viral genome and increased chance for drug resistance.

E) Like bacteria, HIV undergoes spontaneous mutation in the presence of antibiotics, so multiple medications are used simultaneously to reduce the chance of this happening.

117) Why is it not surprising that AIDS patients frequently suffer a viral-induced tumor?

A) HIV genomes integrate into the host cell chromosome. This integration might result in loss of control of the cell cycle (also known as cancer).

B) The immune system's CD4+ T cells are directly responsible for elimination of tumor cells. HIV attacks them and eliminates them, making a person more susceptible to cancer.

C) The therapies for HIV are highly mutagenic, which may lead to cancerous states in people taking the drug regimen.

D) Products of an active HIV infection are highly mutagenic; as a person's illness progresses, these compounds build up and induce a cancerous state.

E) The DNA polymerases of people with AIDS lose any proofreading ability, so any mistakes that happen during DNA replication automatically lead to development of cancer.

118) Would you expect the number of virions to be the same if you measured them by the plaque assay or by counting using the electron microscope? Why?

A) Yes—both methods measure the total number of virus particles in a solution.

B) No—the plaque assay only measures viable virus particles, while the electron microscope cannot distinguish between defective and viable virus.

C) No—you cannot count virus particles by using a plaque assay. You can only get a relative difference in quantity from one preparation of virus particles to another with this method.

D) Yes—only fully functioning viruses will be released from a host cell, so the quantified number of virus particles in a plaque assay should be identical to the number of free virus particles counted by electron microscopy.

119) Why are viroids resistant to nucleases?

A) Having a circular RNA "genome," they are resistant to most exonucleases (that digest the free ends of RNA or DNA).

B) Having a circular RNA "genome," with no protein shell, they are resistant to the protein-degrading activities of nucleases.

C) Nucleases will only digest DNA, not RNA, so viroids are protected.

D) Viroids have only been identified in plants. Plant nucleases cannot digest RNA.

E) Viroids are composed of single stranded RNA; nucleases only act on double-stranded molecules.

120) Would ID50 and LD50 necessarily be the same for a given virus? Why or why not?

A) Yes, because the number of viruses that infect 50% of a test population should also kill 50% of that test population.

B) No, because a virus may be highly infectious (very low ID50 value) but only marginally lethal (very high LD50 value), for example the rhinovirus (common cold virus).

C) No, because very few viruses are lethal, yet many are highly infectious. The two values should ALWAYS be different.

D) Yes, because what we're actually describing here is the infection/ killing of individual cells, not of entire organisms. If a cell is infected, it will always be killed.

E) Yes, because ID50 and LD50 are actually measurements of the same thing: effectiveness of a virus in entering and damaging a host cell.

121) Why is it virtually impossible to eradicate a disease caused by a zoonotic virus?

A) You would have to drive the vector organism extinct to do so.

B) Many vector organisms have multiple stages of their life cycle that can carry a zoonotic virus, which complicates controlling the vector-borne transmission.

C) Many viruses transmitted in this manner may utilize more than one vector organism.

D) Many zoonotic viruses may be able to reside in more than one host organism, complicating control measures.

E) All of the answer choices are correct.

You are a volunteer for Nurses Without Borders and are being sent to a country in Africa. You are excited, because you will have opportunities to go on safari, but you are also somewhat concerned because you have learned from the CDC website that there is currently cholera in the country to which you are going. Patients with cholera experience vomiting and severe diarrhea, producing several liters of liquid stool in a day. This results in signs of dehydration, including sunken eyes, muscle cramps, and in a few cases, convulsions and death. Cholera is caused by the bacterium Vibrio cholerae. You make a list of questions about V. cholerae that you answer with the help of your nursing school study group.

122) The signs and symptoms of cholera are caused by cholera toxin that is synthesized and secreted by the bacteria. The toxin causes chloride and other electrolytes to leave the intestinal cells. Water follows the electrolytes, resulting in an outpouring of water into the intestinal lumen. The gene for cholera toxin is a bacteriophage gene. This situation is an example of ________.

A) lysogenic conversion

B) DNA-mediated transformation

C) mutation

D) vertical gene transfer

E) indirect selection

123) The phage from which the cholera toxin gene originates is a ________ phage.

A) filamentous

B) lytic

C) temperate

D) Gram-positive

E) double-stranded RNA

124) A lysogen is

A) a bacteriophage that carries bacterial DNA integrated into its genome.

B) an insect that carries virus DNA in its genome.

C) a temperate phage that can insert its DNA into the host's DNA.

D) a bacterium that carries phage DNA (a prophage) integrated into its genome.

E) a bacteriophage that lyses its host as a result of its replication cycle.

125) Please select the TRUE statement regarding bacteriophage life cycles.

A) Temperate phages lyse their host cells, whereas lytic phages either lyse their host or integrate their DNA into the host cell's genome.

B) Lytic phages lyse their host cells, whereas temperate phages either lyse their host or integrate their DNA into the host cell's genome.

C) In the bacteriophage life cycle, the entire virus enters the host bacterial cell through a hole in the cell wall.

D) Phage particles seek out their bacterial hosts by means of chemotaxis and then attach to random receptors on the host's cell wall.

E) The burst size is the number of bacterial cells that are lysed as a result of being infected by a bacteriophage such as T4.

126) All bacteriophages must be able to:

1. inject their DNA into the host cell

2. cause a genetic change in the host cell

3. kill the host cell

4. replicate in the absence of a host

5. exit a host cell by extrusion

A) 1, 2, and 4

B) 2 and 3

C) 1, 4, and 5

D) 2 only

E) 1 only

127) In order to treat cholera, antiviral medication must be given to get rid of the bacteriophage that carries the cholera toxin gene.

You are graduating from nursing school in three months and have already lined up a new job. However, your employer informs you that before you start your job, it is mandatory for you to be vaccinated against hepatitis B, a double-stranded DNA virus that can cause the disease hepatitis. Your boyfriend, a biology major, wonders why you need to get the vaccine. You aced your microbiology class and you know a lot about both viruses and vaccines, so you understand why getting this vaccination is essential. You give your boyfriend a mini lesson on this by answering a few of his questions.

128) Your boyfriend asks how animal viruses enter a host cell. You tell him that they can use one of two mechanisms:

A) exocytosis OR fusion

B) endocytosis OR fusion

C) fusion OR phagocytosis

D) endocytosis OR budding

E) budding OR fusion

129) To give more information on virus replication strategies, you explain to your friend the difference between a DNA virus and a RNA virus in terms of replication. You tell him that

A) RNA virus replication always requires a virally encoded RNA polymerase that is an RNA-dependent RNA polymerase; this enzyme uses an RNA template to synthesize a new strand of RNA. DNA viruses use DNA-dependent DNA polymerase in replication.

B) RNA virus replication always requires a virally encoded DNA polymerase, that is an RNA-dependent DNA polymerase; this enzyme uses a DNA template to synthesize a new strand of RNA. DNA viruses use DNA-dependent DNA polymerase in replication.

C) RNA viruses always encode an enzyme called reverse transcriptase, which is an RNA-dependent DNA polymerase that synthesizes DNA from an RNA template. DNA viruses use DNA-dependent RNA polymerase in replication.

D) DNA viruses replicate their genome by means of an RNA-dependent DNA polymerase that synthesizes DNA from an RNA template. RNA viruses replicate their genome by means of a virally encoded replisome.

E) DNA viruses must always first enzymatically degrade one DNA strand before they are able to replicate the remaining strand using the enzyme DNA-dependent RNA polymerase. RNA viruses are single-stranded, so can replicate their genome directly.

130) Your boyfriend wonders whether hepatitis B is really a problematic disease. He says that the job of your immune system is to get rid of viruses and virus-infected cells. You tell him that hepatitis B causes an infection in which the causative agent remains in the body for years or even a lifetime, often without causing symptoms of disease. This type of infection is characterized by the continuous low-level production of viral particles and is called a(n) ________ infection.

A) persistent only

B) persistent AND latent

C) chronic only

D) latent only

E) persistent AND chronic

131) You friend wonders whether the same type of virus can cause both an acute and a persistent infection? You answer

A) Yes—the initial infection might be acute but the virus can later become latent by becoming integrated into the host cell genome. 

B) No—a virus causes either an acute infection or a persistent infection, but never both. 

C) No—if the initial infection is acute, the virus would have to mutate in the host before being able to cause a persistent infection.

D) Yes—acute and persistent infections are really the same thing except that people with persistent infections recover more quickly than those with acute infections.

E) Yes—acute and persistent infections are really the same thing except that people with acute infections recover more quickly than those with persistent infections.

132) You tell your friend that you are happy to be receiving your vaccination because hepatitis B is associated with hepatocellular carcinoma (liver cancer). Select the FALSE statement regarding viruses and cancer. 

A) Viruses that lead to cancer formation are called oncogenic viruses.

B) The most common viral causes of tumors are certain DNA viruses such as hepatitis B virus.

C) Some viruses carry an oncogene—infection with these viruses interferes with the host cell's own growth-control mechanisms.

D) The majority of tumors are caused by oncogenic viruses but some may be caused by mutations in host genes that regulate cell growth.

E) Viruses that insert their genome into the host cell's chromosome may cause changes at the insertion site, converting a proto-oncogene into an oncogene.

133) Most enveloped viruses, like hepatitis B, are released by budding, a process whereby the virus acquires its envelope. Before budding occurs, virally encoded protein spikes insert into specific regions of the host cell's membrane. Given this information, which of the following would you tell your friend best describes the structure of the viral envelope?

A) Phospholipid bilayer

B) Phospholipid bilayer with host-derived proteins.

C) Phospholipid bilayer studded with both virus- and host-derived proteins.

D) Protein layer with host-derived spikes.

E) Phospholipid monolayer studded with virus- and host-derived proteins.

134) If you had three tubes of flu viruses and you exposed tube 1 to protease, tube 2 to protease and RNase, and tube 3 to protease and DNase, and the contents of tube 2 were be degraded, you would be able to conclude that

A) an RNA virus.

B) a DNA virus.

C) a protein virus.

D) resistant to proteases.

E) an opportunist.