Deck 26: Introduction to Viruses

Question 1

Which of the following statements best supports the argument that viruses are nonliving?

A) They do not carry out metabolic processes.
B) Their DNA does not encode proteins.
C) They have RNA rather than DNA.
D) They do not evolve.

Answer 1

A

Question 2

The host range of a virus is determined by whether ________.

A) the enzymes carried by the virus are compatible with the host
B) the genome of the virus is made of DNA or RNA
C) it is an enveloped or non-enveloped virus
D) the proteins on virus surface can bind with proteins on the host surface

Answer 2

D

Question 3

Use the following figure and information to answer the question. Cells were infected with approximately 1,000 copies of either virus A or virus B at the 0 time point. At five-minute intervals, a sample of the virus and cell mixture was removed. All intact cells were removed from the sample, and the number of viruses per milliliter of culture was determined.
Based on the data provided, the lytic cycle of virus B is closest to ________.

A) 15 minutes
B) 30 minutes
C) 45 minutes
D) 60 minutes

Answer 3

D

Question 4

A newly identified virus has a single-stranded RNA genome that is used as mRNA after infection. Its capsid is 25-30 nm in diameter and contains 180 identical capsomeres. Which of the following processes would be the best to follow to analyze the reproduction of this virus in a host cell?

A) DNA replication rate
B) mRNA splicing
C) translation rate
D) formation of new transcription factors

Question 5

Which of the following events or characteristics is the most likely explanation for why an individual experiences regular herpesvirus-mediated cold sore or genital sore flare-ups?

A) They have been reinfection by exposure to a different, but closely related herpesvirus strain.
B) They have been reinfection by exposure to the same herpesvirus strain.
C) Copies of the herpesvirus genome permanently maintained in host nuclei are periodically "activated."
D) Copies of herpesvirus particles that have escaped the immune system periodically experience conditions that allow them to replicate and infect cells.

Question 6

Which of the following descriptions correctly identifies a main structural difference between viruses with envelopes and viruses without envelopes?

A) Only viruses with envelopes have their contents enclosed by a layer containing lipids
B) Only viruses with envelopes package their genetic material by engulfing it.
C) Only viruses without envelopes can release their genetic material into the cytoplasm of the host.
D) Only viruses without envelopes interact with receptor proteins on the surface of the host cell.

Question 7

Since viral gene expression is regulated by the same machinery as host cell gene expression, which of the following is most likely involved in regulating expression of bacteriophage genes?

A) regulation via acetylation of histones
B) positive control mechanisms rather than negative
C) coordinate control of more than one gene in an operon
D) reliance on transcription activators

Question 8

Use the figures to answer the question. Which of the three types of viruses shown would you expect to have glycoproteins among its components?

A) I only
B) III only
C) I and II only
D) II and III only

Question 9

Which of the following correctly describes the viral assembly process?

A) Host cell chaperone proteins mediate assembly of viral components.
B) Assembly proteins coded for by the host genome mediate assembly of viral components.
C) Assembly proteins coded for by the viral genome mediate assembly of viral components.
D) New viral components self-assemble without help from cellular components.

Question 10

Use the figures to answer the question. Which of the three types of viruses shown in the figure would you expect to include a capsid(s)?

A) I only
B) III only
C) I and II only
D) I, II, and III

Question 11

Use the following information to answer the question.
Poliovirus is an RNA virus of the picornavirus group, which uses its RNA as mRNA. The RNA genome has a 5′ RNA cap instead of a 5′ methyl-G cap. This is followed by a non-translated leader sequence and then a single long protein-coding region (~7,000 nucleotides) followed by a poly-A tail. Infected cells were incubated with radioactive amino acids and viral proteins were isolated. After a short incubation with radioactive amino acids only very long viral proteins were seen, while longer periods of labeling result in several short polypeptides of different lengths.
Which of the following conclusions is most consistent with the results described?

A) Host cell ribosomes translate the viral coding region and poly-A tail at different times resulting in the different populations of proteins.
B) The RNA is first translated into a single long protein, which is then cleaved into shorter ones.
C) The RNA is translated into short polypeptides, which are then assembled into large complexes.
D) The large radioactive polypeptides are coded by the host, whereas the short ones are coded for by the virus.

Question 12

Use the following figure and information to answer the question. Cells were infected with approximately 1,000 copies of either virus A or virus B at the 0 time point. At five-minute intervals, a sample of the virus and cell mixture was removed. All intact cells were removed from the sample, and the number of viruses per milliliter of culture was determined and plotted in the graph above.
In a second experiment, 1 mL of each viral sample collected at 90 minutes post infection was mixed with new, uninfected cell cultures. Which of the following best describes these new cultures?

A) The new culture infected with virus A will require 60 minutes before new viral particles will be released into the culture.
B) The new culture infected with virus A will result in more infected cells than the new culture infected with virus B.
C) The new culture infected with virus B will have a shorter lytic cycle than seen in the original virus B culture.
D) The new culture infected with virus B will plateau with approximately 50,000 viral particles per milliliter of culture.

Question 13

The virus genome and viral proteins are assembled into virus particles during which of the following parts of the reproductive cycle?

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

Question 14

Electron micrographs of herpes simplex virus (HSV) infection show the following progression; the intact virus first interacts with cell-surface proteoglycans and then with specific receptors, viral capsids dock with nuclear pores, and, finally, capsids go from being full to being "empty." Which of the following statements best fits these observations?

A) Viral capsids are needed for the cell to become infected; its proteins mediate binding with specific cells.
B) The viral envelope is not required for infectivity; its components do not enter the nucleus.
C) Only the genetic material of the virus is involved in infection; it is injected into the cytoplasm like the genome of a phage.
D) The viral envelope mediates entry into the cell; the viral genome is all that enters the nucleus.

Question 15

Viruses can carry out which of the following processes?

A) They can manufacture their own ATP, proteins, and nucleic acids.
B) They can use the host cell machinery to make copies of viral genomes and viral proteins.
C) They can use the host cell as a source of energy allowing viral machinery to replicate the virus.
D) They can replicate while within a host cell as well as when they are between host cells.

Question 16

Use the following figure and information to answer the question below. Cells were infected with approximately 1,000 copies of either virus A or virus B at the 0 time point. At five-minute intervals, a sample of the virus and cell mixture was removed. All intact cells were removed from the sample, and the number of viruses per milliliter of culture was determined.
Based on the data provided, the lytic cycle of virus A is closest to ________.

A) 15 minutes
B) 30 minutes
C) 45 minutes
D) 90 minutes

Question 17

Which of the following characteristics is typical of the lytic cycle of a bacteriophage?

A) Viral DNA incorporates into the host genome.
B) The viral genome replicates without destroying the host.
C) The host membrane ruptures, releasing many phages.
D) The host sequesters viral particles in the lysosome.

Question 18

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

A) The viral genes immediately turn the host cell into a lambda-producing factory. Then the host lyses.
B) The product of one prophage gene is made and it activates most of the other prophage genes.
C) The phage genome is integrated in the host chromosome where it is passed on to daughter cells through binary fission.
D) The phage DNA is copied and accumulates in the cytoplasm. Then a trigger causes capsid proteins to be made and phages are assembled.

Question 19

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 more viral RNA strands.

Question 20

Which of the following characteristics correctly describes retroviruses?

A) They are not destroyed or deactivated by heating.
B) They can only reproduce by infecting bacteria.
C) They have a single-stranded DNA that is integrated into the host cell genome.
D) They have a single-stranded RNA that acts as a template for DNA synthesis.

Question 21

A researcher is studying a single plant infected with tobacco mosaic virus (TMV). She crushes three of the plant's leaves in a small amount of water and stores the sample in the refrigerator overnight. The next day she sprays the mixture onto a new set of tobacco plants she had recently trimmed and repotted. Which of the following results will most likely occur?

A) The plant cuticle would protect them from infection and they would continue growing as before.
B) The plants would develop the typical symptoms of TMV infection and would be able to transmit the disease.
C) These plants would not show any disease symptoms but vertical transmission would cause their offspring to be diseased.
D) The plants would become infected with TMV, but extracts from these plants would be unable to infect other plants.

Question 22

The difference between vertical and horizontal transmission of plant viruses is that vertical transmission ________.

A) transfers viruses from a parent plant to its progeny, and horizontal transmission transfers viruses from one plant to another plant
B) spreads viruses from upper leaves to lower leaves of the plant, and horizontal transmission spreads viruses among leaves at the same general level
C) spreads viruses from trees and tall plants to bushes and other smaller plants, and horizontal transmission spreads viruses among plants of similar size
D) transfers DNA from a plant of one species to a plant of a different species, and horizontal transmission spreads viruses among plants of the same species

Question 23

Which of the following statements correctly describes vaccines and how they help prevent viral infection?

A) Vaccines are active versions of a virus that stimulate an immune reaction in a person.
B) Vaccines are inactive versions of a virus that stimulate an immune reaction in a person.
C) Vaccines are infectious proteins that stimulate an immune reaction in a person.
D) Vaccines are functional pathogens that stimulate an immune reaction in a person.

Question 24

Which of the following correctly describes a strategy that bacteria have evolved to defend against infection by phage?

A) The CRISPR-Cas system allows bacteria to recognize phage strains that have previously infected that bacterial lineage and targets the phage DNA for destruction.
B) Bacteria secrete enzymes that diffuse away from the cell and digest phage capsid proteins so the virus cannot infect the cells.
C) Bacteria methylate phage DNA as it enters the cell, targeting it for destruction by restriction enzymes.
D) The lysogenic cycle allows bacteria evolve inhibitors that bind with the phage DNA they contain so their daughter cells will no longer be infected.

Question 25

Which of the following types of viral genomes could be copied using reverse transcriptase?

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

Question 26

A population of viruses with similar characteristics is called a ________.

A) class
B) species
C) type
D) genome

Question 27

Which of the following viruses would most likely contain 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

Question 28

Humans have harmless E. coli strains that reside in the intestines. O157:H7 is an E. coli strain reported to cause several food poisoning deaths. Evidence suggests that the virulence of O157:H7 is caused by genes from a virus that infects bacteria. Considering this evidence, which of the following statements most likely explains how the O157:H7 population acquired the genetic variation that distinguishes it from the harmless E. coli strains?

A) The virus entered the bacterial cell, allowing the bacteria's cellular machinery to create new viruses.
B) Viral envelope proteins bound receptors on the bacteria, allowing the viral genetic material to enter the cytoplasm and be translated into proteins that increased that bacterium's virulence.
C) The virus entered the cell and reassorted to acquire specific genes from the bacteria to increase the virulence of the virus.
D) The virus infected the bacterium, and the bacterial population replicated with a copy of the phage genome in each new bacterium.

Question 29

Which of the following responses explain why the apparent high rate of mutation in RNA viruses?

A) RNA nucleotides are more unstable than DNA nucleotides.
B) RNA virus genome replication does not involve proofreading.
C) RNA viruses can incorporate a variety of nonstandard bases.
D) RNA viruses are more sensitive to mutagens.

Question 30

Which of the following best defines prions?

A) mobile segments of DNA that can disrupt host gene expression
B) 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 proteins that can cause disease

Question 31

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

Question 32

Viruses require host cell's machinery to make copies of themselves. However, some viruses that infect humans require mechanisms that do not normally occur in human cells. Which of the following describes how the viruses can replicate in human cells?

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 found in the host cells.
C) The virus can enter these cells but new viruses will not be made until an environmental change triggers a switchover.
D) Viruses can stay in a quiescent state until the host cell evolves this ability.

Question 33

If a viral host cell has a mutation that interferes with the addition of carbohydrates to proteins during processing in the Golgi apparatus, which of the following processes is most likely to occur?

A) Viruses released by that cell would have a decreased ability to infect cells than the virus that originally infected the cell.
B) Viruses released by that cell are novel and would result in infections with higher mortality rates.
C) The virus-encoded protease would be unable to cleave large viral proteins into smaller, functional polypeptides.
D) The virus would be unable to reproduce within the host cell.

Question 34

A virus consisting of a single strand of RNA, which is reverse transcribed into complementary DNA, is referred to as a ________.

A) protease
B) retrovirus
C) bacteriophage
D) non-enveloped virus

Question 35

If a viral host cell has a mutation that interferes with the addition of carbohydrates to proteins during processing in the Golgi apparatus, which of the following processes is most likely to occur?

A) The viral envelope proteins would not have glycoproteins added to them and might not arrive at the host plasma membrane.
B) The viral capsid proteins would not have glycoproteins added to them and might not arrive at the host plasma membrane.
C) The viral core proteins would not have glycoproteins added to them and might not arrive at the host plasma membrane.
D) The virus would be unable to reproduce within the host cell.

Question 36

Azidothymidine (AZT) is a reverse transcriptase inhibitor that was part of the first class of antiviral drugs developed to treat HIV infection. Which of the following correctly describes how these drugs inhibited HIV infection?

A) The drugs targeted and destroyed the viral genome before it could be reverse transcribed into DNA.
B) The drugs bonded to the viral dsDNA and prevented it from being able to be used as a template for replication.
C) The drug bonded to the viral reverse transcriptase enzyme and prevented it from making a DNA copy of viral RNA.
D) The drugs prevented host cells from producing the enzymes used by the virus to replicate its genome.

Question 37

A few minutes of incubation at room temperature in the laboratory will inactivate HIV, but the flu virus is still active after incubating for several hours. What are the practical consequences of these findings?

A) The flu virus is more sensitive to changes in temperature than HIV.
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 will have more of an effect on reducing the spread of HIV than on reducing the spread of the flu.

Question 38

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

A) taking vitamins before being exposed to various viruses
B) getting vaccinated to certain viruses
C) taking antibiotics to inhibit bacterial growth
D) taking drugs that inhibit transcription

Question 39

Which of the following statements correctly describes a characteristic of viral infections in plants?

A) They can be controlled with antibiotics.
B) They can spread within a plant via plasmodesmata.
C) They have little effect on plant growth.
D) They are not spread by animals.

Question 40

Which of the following statements correctly describes a difference between viruses and prions?

A) Viruses infect many types of cells, whereas prions infect only prokaryotic cells.
B) Viruses have protein capsids surrounding nucleic acids, whereas prions are made only of nucleic acids.
C) Viruses have genomes composed of RNA, whereas prions have genomes composed of DNA.
D) Viruses replicate using its host's DNA replication machinery, whereas prions replicate using host's translation machinery.

Question 41

Which of the following methods would be best to use for distinguishing between an infectious agent that is a virus and one that is a prion?

A) Treat the substance with enzymes that destroy all nucleic acids, and then determine whether the substance is still infectious.
B) Filter the substance to remove all elements smaller than what can be easily seen under a light microscope.
C) Culture the substance on nutritive medium, away from any cells.
D) Treat the sample with proteases that digest all proteins, and then determine whether the substance is still infectious.

Question 42

Which of the following characteristics, structures, or processes is common to both bacteria and viruses?

A) metabolism
B) ribosomes
C) genetic material composed of nucleic acid
D) cell division

Question 43

To cause a human pandemic, the H5N1 avian flu virus would have to ________.

A) spread to primates such as chimpanzees
B) develop into a virus with a different host range
C) become capable of human-to-human transmission
D) become much more pathogenic

Question 44

RNA viruses require their own supply of certain enzymes because ________.

A) host cells rapidly destroy the viruses
B) host cells lack enzymes that can replicate the viral genome
C) these enzymes translate viral mRNA into proteins
D) these enzymes penetrate host cell membranes

Question 45

A person is most likely to recover from a cold due to viral infection if the infected cells are able to perform which of the following processes?

A) normal cell division
B) absorption of antibiotics
C) production and release viral protein
D) transcription of viral mRNA

Question 46

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.

Question 47

An infectious substance capable of causing disease in plants is isolated and researchers want to determine whether the substance is a bacterium or a virus. Which of the following methods will best allow them to determine the type of infectious agent they have isolated?

A) Treat the substance with enzymes that destroy all nucleic acids, and then determine whether the substance is still infectious.
B) Culture the substance with plant cells, and then determine whether the cells lyse.
C) Treat the sample with proteases that digest all proteins, and then determine whether the substance is still infectious.
D) Culture the substance on nutritive medium, away from any plant cells.

Question 48

A bacterium is infected with an experimentally constructed bacteriophage composed of the T2 phage protein coat and T4 phage DNA. The new phages produced would have ________.

A) T2 protein and T4 DNA
B) T4 protein and T2 DNA
C) T2 protein and T2 DNA
D) T4 protein and T4 DNA

Question 49

Which of the following statements best reflects what we know about how influenza virus moves between species?

A) In an animal, such as a pig, the influenza virus is mutated and replicated in alternate arrangements so that humans who eat the pig products can be infected.
B) An influenza virus from a human epidemic or pandemic infects birds; the birds replicate mutant versions of that virus and then pass the new forms back to humans.
C) An influenza virus fuses with a different type of virus (like HSV) and gains new DNA which enable the new virus to be transmitted to a wider variety of host species.
D) An animal, such as a pig, is infected with more than one strain of the influenza virus and the genomes reassort into new combinations that can facilitate spread to other species.

Question 50

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 host 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 for the presence of 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) The RNA of related viruses can reassort during viral assembly resulting in new genetic combinations.
D) The human was likely infected with various bacterial strains that contained all three RNA viruses.

Question 51

Emerging viruses arise by ________.

A) mutation of existing viruses
B) the spread of existing viruses to new host species
C) the spread of existing viruses more widely within their hostspecies
D) all of the above

Question 52

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) RNA genomes are less stable than DNA genomes and the RNA breaks introduce mutations.
D) Viral RNA is translated by host cell ribosomes and viruses use slightly different codons.

Question 53

Use the following information to answer the question.
The herpes viruses are 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 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, and infect others.
Which of the following treatments would have the best chance of lowering the number of new cases of infection?

A) Vaccinate of all persons with preexisting cases of herpes simplex virus.
B) Interfere with new viral replication in preexisting cases of herpes simplex virus.
C) Treat herpes simplex virus lesions to shorten the breakout.
D) Educate people about ways to disinfect surfaces that came in contact with herpes simplex virus.

Question 54

Which of the following correctly explain the effect that treating a viral infection with antibiotics has on the course of the infection?

A) The infection's length will remain the same because antibiotics have no effect on eukaryotic or virally encoded enzymes.
B) The infection's length will remain the same because viruses do not have DNA or RNA, and so antibiotics do not affect them.
C) The infection's length will be shorter because antibiotics activate the immune system, and this decreases the severity of the infection.
D) The infection's length will be shorter because antibiotics can prevent viral entry into the cell by binding to host-receptor proteins.