Deck 13: Viruses, Viroids and Prions

Question 1

The protein coat of a virus

A)is called a capsomere.
B)is called a capsid.
C)protects the nucleic acid.
D)is involved in recognition of host cell receptors.
E)is called a capsid, protects the nucleic acid AND is involved in recognition of host cell receptors.

Answer 1

E

Question 2

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 within a given preparation.

Answer 2

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 within a given preparation.

Question 3

A virion is a(n)

A)pathogenic virus.
B)subviral particle.
C)complete, extracellular virus particle.
D)enveloped virus particle.

Answer 3

C

Question 4

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.

Question 5

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 utilizes 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.

Question 6

The term filterable viruses was coined by

A)Beijerinck.
B)Iwanowsky.
C)Twort.
D)d'Herelle.

Question 7

Viruses

A)probably keep the numbers of bacteria in check.
B)have no effect on the number of bacteria.
C)increase the number of bacteria.
D)are active in passing DNA from one bacterium to another.
E)probably keep the numbers of bacteria in check AND are active in passing DNA from one bacterium to another.

Question 8

Which does not refer to the shape of a virus?

A)icosahedral (isometric)
B)helical
C)complex
D)bacillus

Question 9

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).A prime example of this is the rhinovirus (common cold virus).
C.No, because very few viruses are lethal, yet many are highly infectious.The 2 values should ALWAYS be different.
D.Yes, because what we're actually describing here is infection/killing of individual CELLS, not of entire organisms.If a cell is infected, it will always be killed.

Question 10

Is antigenic shift alone likely to lead to influenza pandemics?
A.Yes-ONLY antigenic shift can lead to the large-scale mixing of gene elements required to produce a pandemic flu strain.
B.No-ONLY antigenic DRIFT can lead to the large-scale mixing of gene elements required to produce a pandemic flu strain.
C.Perhaps-but it would most likely be a mixture of antigenic shift AND drift that would result in a pandemic strain.
D.No-antigenic SHIFT is responsible for changes in the hemagglutinin protein, while antigenic DRIFT is responsible for changes in the neuraminidase protein.You must have changes in both to lead to a pandemic strain.

Question 11

Outside of living cells, viruses are

A)scavenging glucose.
B)slowly stockpiling ATP from the mitochondria.
C)using cilia to move to the next host.
D)metabolically inert.

Question 12

The viral envelope closely resembles the

A)prokaryotic cell wall.
B)capsomere.
C)eukaryotic cell membrane.
D)cytoplasm.

Question 13

Why are viroids resistant to nucleases?
A.Having a circular RNA 'genome,' they are resistant to the digestion of most exonucleases (that nibble/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.

Question 14

Viruses that infect bacteria are referred to as

A)viralcidens.
B)bacteriocidins.
C)bacterialogens.
D)bacteriophages.

Question 15

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-so, as a person's illness progresses, these mutagenic compounds build up and are more capable of inducing a cancerous state.

Question 16

Crystallization of Tobacco Mosaic Virus was accomplished by

A)Berkley.
B)Stanley.
C)Iwanowsky.
D)Twort.

Question 17

The shape of the virus is determined by its

A)nucleic acid.
B)capsid.
C)envelope.
D)tail.

Question 18

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 utilize 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.

Question 19

Why is it virtually impossible to stamp out a disease caused by a zoonotic virus?
A.You'd 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 1 host organism, complicating control measures.
E.All of the above are correct.

Question 20

A virion is composed of

A)lipid, protein, and either RNA or DNA.
B)protein and either RNA or DNA.
C)protein and both, RNA and DNA.
D)protein, either RNA or DNA, and possibly lipid.

Question 21

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.

Question 22

The replicative form of nucleic acid in filamentous phages is

A)dsDNA.
B)dsRNA.
C)positive ssRNA.
D)negative ssDNA.

Question 23

An exit method used by viruses which does not immediately destroy the host bacterium is

A)lysis.
B)inversion.
C)extrusion.
D)excising.

Question 24

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.

Question 25

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.

Question 26

Most phages that contain single-stranded DNA

A)are extruded.
B)contain a positive-sense DNA strand.
C)have their DNA transformed to double-stranded DNA before replication and transcription occur.
D)All of the choices are correct.

Question 27

What part of the

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.

Question 28

Assembly of the T4 phage

A)may involve some self-assembly.
B)may involve the use of scaffolds.
C)is completely self-assembly.
D)is completely dependent on scaffolds.
E)may involve some self-assembly AND may involve the use of scaffolds.

Question 29

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

A)1 per host cell.
B)5 per host cell.
C)200 per host cell.
D)1000 per host cell.

Question 30

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

Question 31

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.

Question 32

Phage-encoded enzymes are

A)all produced simultaneously.
B)produced in a sequential manner.
C)strictly host enzymes.
D)used to customize the cell for viral production.
E)produced in a sequential manner AND used to customize the cell for viral production.

Question 33

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

A)T9.
B)T4.
C)beta.
D)gamma.

Question 34

The filamentous phages all contain

A)single-stranded DNA.
B)double-stranded DNA.
C)single-stranded RNA.
D)double-stranded RNA.

Question 35

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

Question 36

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

A)lysogenic phages.
B)lytic phages.
C)virulent phages.
D)segmented phages.

Question 37

Which is a filamentous phage?

A)M13
B)T4
C)lambda
D)phi X174

Question 38

Bacteria infected with filamentous phages are termed

A)temperate cells.
B)plaque-producing cells.
C)virulent strains.
D)carrier cells.

Question 39

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.

Question 40

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

A)1 minute.
B)10 minutes.
C)30 minutes.
D)1 day.

Question 41

The RNA phages contain only a single positive-sense strand of RNA.

Question 42

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.
C)lysed bacteria pose no threat.
D)a single phage can be genetically engineered to infect many different species of bacteria.

Question 43

Lysogenized cells

A)are immune to any further infection by any virus.
B)are immune to infection by the same virus.
C)may have new properties.
D)respond to infection with the SOS response.
E)are immune to infection by the same virus AND may have new properties.

Question 44

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

A)incomplete.
B)mutated.
C)defective.
D)vegetative.

Question 45

A lysogenic cell contains viral DNA, a prophage, integrated into the host chromosome.

Question 46

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.

Question 47

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

Question 48

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.

Question 49

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

A)identical DNA sequences in both.
B)the phage's ability to synthesize enzymes to enter the bacterium.
C)similar RNA nucleotides in both.
D)the similarity in enzyme metabolism.
E)the phage's ability to synthesize enzymes to enter the bacterium AND similar RNA nucleotides in both.

Question 50

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

Question 51

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

Question 52

Regarding phage replication,

A)the majority of phages are temperate.
B)when integrated into host DNA, the phage DNA is called a prophage.
C)lambda is a good example of a temperate phage.
D)All of the choices are correct.

Question 53

A limiting factor for viral infection is

A)internal metabolic temperature of the host cell.
B)nutrition of the host cell.
C)stage of cell cycle of the host cell.
D)presence of specific receptor molecules on the host cell.

Question 54

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)prion protein.
D)lysogenic conversion.

Question 55

Filamentous virus is incapable of causing a lytic infection.

Question 56

DNA is protected from restriction enzymes by being

A)sequestered in a lysosome.
B)turned into RNA.
C)methylated.
D)made into double stranded RNA.

Question 57

Once inside the host cell, phage DNA

A)is replicated.
B)is transcribed.
C)may get degraded by bacterial nucleases.
D)All of the choices are correct.

Question 58

Specialized transduction

A)involves the random transmission of any gene.
B)involves the transfer of a few specific genes.
C)utilizes a defective virus.
D)only involves genes near the viral DNA integration site.
E)involves the transfer of a few specific genes, utilizes a defective virus AND only involves genes near the viral DNA integration site.

Question 59

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

A)destruction of the viral genes.
B)complete lysis of the bacterial culture.
C)mutation of the DNA.
D)destruction of the viral repressor through host protease activity.
E)complete lysis of the bacterial culture AND destruction of the viral repressor through host protease activity.

Question 60

RNA phages usually contain

A)dsRNA.
B)dsDNA.
C)ssRNA.
D)ssDNA.

Question 61

Transduction often involves defective virus.

Question 62

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

A)-virus.
B)-viridae.
C)-viscous.
D)-eieio.

Question 63

The restriction-modification system always has two genes involved, the cutting enzyme and the methylating enzyme.

Question 64

The family to which the Rhinovirus belongs is the

A)Picornaviridae.
B)Enterovirus.
C)Enteroviridae.
D)Picornavirus.

Question 65

There are _______ families of DNA containing viruses that infect vertebrates.

A)two
B)four
C)five
D)seven

Question 66

Enveloped viruses

A)just require a stamp.
B)have an outer lipid bilayer membrane containing various proteins.
C)are surrounded by an additional layer of carbohydrate.
D)envelope a cell.

Question 67

Resistance of some animals to certain viral diseases is based on

A)lack of spikes for attachment.
B)phagocytosis of the virus by the host cell.
C)the presence of the viral envelope.
D)lack of specific receptors on the host cell.

Question 68

The terms isometric, icosahedral and pleomorphic refer to

A)viral life cycles.
B)forms of nucleic acid.
C)types of viral envelopes.
D)shapes of viruses.

Question 69

All single-stranded DNA phages are extruded.

Question 70

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

Question 71

A key feature of all viral infections is the

A)integration of viral DNA into host DNA.
B)disintegration of host DNA.
C)addition of a lipid membrane to the virus.
D)separation of viral nucleic acid from the capsid.

Question 72

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.

Question 73

Viruses are commonly referred to by their _________ name.

A)locale
B)genus
C)disease
D)species
E)disease AND species

Question 74

The common species name of the virus is 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.

Question 75

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

Question 76

There are _______ families of RNA containing viruses that infect vertebrates.

A)two
B)five
C)seven
D)fourteen

Question 77

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

A)a tail.
B)the envelope.
C)a capsid.
D)spikes.

Question 78

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

A)acute.
B)balanced.
C)determinant.
D)persistent.

Question 79

The receptors to which animal virus attachment proteins usually bind are

A)proteins.
B)carbohydrates.
C)nucleic acid.
D)lipids.
E)glycoproteins.

Question 80

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.