Viruses can vary with respect to all of the following characteristics except _____. (eText Overview)
A)the presence or absence of a membranous envelope
B)the presence or absence of metabolic machinery
C)single- or double-stranded nucleic acids
D)the type of host cell it can infect
E)DNA or RNA as the genetic material
B
A microbiologist analyzes chemicals obtained from an enveloped RNA virus that infects monkeys. He finds that the viral envelope contains a protein characteristic of monkey cells. Which of the following is the most likely explanation? ( Concept 19.1)
A)The viral envelope forms as the virus leaves the host cell.
B)The virus fools its host by mimicking its proteins.
C)The virus forced the monkey cell to make proteins for its envelope.
D)The virus is a prophage.
E)Its presence is a result of the monkey's immunological response.
A
Which of the following, if any, may be a component of a virus? ( Concept 19.1)
A)phospholipid bilayer
B)double-stranded (ds) DNA
C)protein
D)single-stranded (ss) RNA
E)All of the listed responses are correct.
E
Viruses that infect bacteria are called _____. ( Concept 19.1)
A)bacterioviruses
B)retroviruses
C)proviruses
D)bacteriophages
E)capsomeres
D
HIV, the virus that causes AIDS, only infects certain cells within the immune system. This is because _____. ( Concept 19.2)
A)the virus gets into all cells, but the viral RNA is immediately destroyed in all but a small number of immune system cells
B)infection requires the presence of a specific DNA sequence that is only present in the genome of certain immune system cells
C)the virus is not very mobile within the body and only comes into contact with a limited number of immune cells
D)other cells produce toxins that destroy the virus before infection can take place
E)the virus binds to specific receptors that are only present on certain immune cells
E
Cancer cells often have protein receptor molecules on their surfaces that differ from those on normal body cells. Given this fact, how might viruses be used to treat cancer? ( Concept 19.2)
A)Viruses could be engineered to infect only cancer cells by altering viral surface proteins to recognize only the receptors on cancer cells.
B)Viruses could be engineered to attach to the surface receptors on cancer cells to alert the immune system to the presence of cancer.
C)Viruses are pathogenic and will infect the host. This treatment will not work.
D)Viruses could be used to carry genes exclusively to the normal body cells. These genes could encode proteins that would help destroy the cancer cells.
E)Viruses sometimes cause cancer. This is a bad idea.
A
Why are phages useful in treating bacterial infections in humans? ( Concept 19.2)
A)Because of their host specificity, they only attack bacteria. They do not affect eukaryotic cells.
B)Because of their specificity, a phage can be used that will only infect the pathogenic bacteria, leaving helpful bacteria alone.
C)Because phages are free to evolve, bacteria are less likely to develop a lasting resistance to them.
D)They are not useful, and the practice has been banned in all countries.
E)The first three answers are correct.
E
Which of the following can a virus do without a host cell? ( Concept 19.2)
A)transcribe DNA
B)produce ATP for energy
C)produce nucleotides for use in replication and transcription
D)synthesize proteins
E)None of the listed responses is correct.
E
When a virus infects an E. coli cell, what part of the virus enters the bacterial cytoplasm? ( Concept 19.2)
A)only the nucleic acid
B)the tail fibers
C)the protein capsid and enclosed nucleic acid
D)the entire virus
E)the protein capsid only
A
The phage reproductive cycle that kills the bacterial host cell is a _____ cycle, and a phage that always reproduces this way is a _____ phage. ( Concept 19.2)
A)lysogenic ... virulent
B)lysogenic ... temperate
C)lytic ... lysogenic
D)virulent ... lytic
E)lytic ... virulent
E
In the lytic life cycle of phages _____. ( Concept 19.2)
A)the entire phage is taken into the bacterium
B)DNA replication is not part of the life cycle
C)phage DNA is incorporated into the host cell's genome
D)the viral capsid is assembled according to the genetic information of the bacterium
E)the cell typically dies, releasing many copies of the virus
E
Restriction enzymes help defend bacteria against viral infections by _____. ( Concept 19.2)
A)preventing entry of the viral DNA into the cell
B)preventing the synthesis of viral capsomeres in the cell
C)preventing the binding of the virus to the cell surface
D)cutting viral DNA once it has entered the cell
E)preventing integration of the viral genome into the host chromosome
D
A phage that inserts itself into the host DNA is called _____. ( Concept 19.2)
A)lysogenic
B)a bud
C)semipermeable
D)a bacteriophage
E)a capsomere
A
A prophage is a(n) _____. ( Concept 19.2)
A)prion that has been integrated into a bacterial cell's chromosome
B)emerging virus
C)type of retrovirus
D)virus that infects bacteria
E)viral genome that has been incorporated into a bacterial cell's chromosome
E
In the lysogenic cycle of phages _____. ( Concept 19.2)
A)only a small number of the viral genes are expressed
B)the viral nucleic acid is replicated along with the host DNA
C)the nucleic acid core of the phage is all that enters the host cell
D)the viral nucleic acid inserts itself into the host chromosome
E)All of the listed responses are correct.
E
What is the origin of the phospholipid membrane that envelops many animal viruses? ( Concept 19.2)
A)It is assembled from free phospholipids floating in the cell's cytoplasm.
B)It is assembled in the ER based on signals sent out by the viral genome.
C)It is "stolen" from the host cell, but it contains some proteins encoded by the viral genome.
D)It is "stolen" from the host cell and contains only host cell proteins and phospholipids.
E)It is produced by viral enzymes and contains only viral proteins and phospholipids.
C
Why can flare-ups of herpesvirus infection recur throughout a person's life? ( Concept 19.2)
A)Herpesvirus is very common in the environment, so it is easy for a person to become re-infected.
B)The herpesvirus always kills its host cell when it leaves. Cycles of cell death cause the recurring flare-ups.
C)Herpesvirus may cloak itself in a cell's nuclear envelope, making it very difficult for the immune system to recognize it.
D)The herpesvirus becomes a prophage during the lysogenic cycle of the infection, so the viral genome is recombined with the host DNA.
E)Herpesvirus can leave its DNA behind as minichromosomes in nerve cell nuclei. Stress can trigger another round of virus production, producing characteristic blisters and sores.
E
How do retroviruses, such as HIV, differ from other viruses? ( Concept 19.2)
A)They contain DNA that is used as a template to make RNA.
B)They can transcribe a DNA copy from a RNA template.
C)They contain nucleic acids that code for proteins.
D)They can reproduce only inside living cells.
E)They have much simpler reproductive cycles than other RNA viruses.
B
Reverse transcription, carried out by retroviruses, is the process by which _____. ( Concept 19.2)
A)information is copied from a protein molecule into RNA
B)RNA information is "read" to form a protein molecule
C)DNA information is copied into RNA
D)DNA is duplicated
E)RNA information is copied into DNA
C
Which statement below is a correct comparison of a "regular" RNA virus and an RNA retrovirus? ( Concept 19.2)
A)Only the regular RNA virus produces DNA from an RNA template.
B)Only the regular RNA virus performs transcription.
C)Only the RNA retrovirus performs translation.
D)Both produce protein coats via translation of mRNA.
E)Only RNA retroviruses produce DNA using DNA replicase.
D
When comparing DNA and RNA viruses, which mutate more quickly, and why? ( Concept 19.2)
A)DNA viruses, because the host cell's proofreading enzymes do not work on viral DNA
B)They all mutate at the same rate.
C)RNA viruses, because no proofreading is done on RNA molecules
D)DNA viruses, because they usually have larger genomes and thus more loci for mutations to occur
E)RNA viruses, because RNA is single-stranded and thus more prone to mutations
C
The symptoms of a viral infection in a person can be caused by _____. ( Concept 19.3)
A)the death of infected cells
B)toxic viral components, such as envelope proteins
C)the reaction of the individual's immune system to the infection
D)the production of toxins by infected cells
E)All of the listed responses are correct.
E
Vaccines for viral diseases are _____ and help prevent infection by _____. ( Concept 19.3)
A)protease inhibitors ... preventing synthesis of envelope proteins
B)harmless derivatives of pathogenic viruses ... stimulating the immune system to mount a defense against the actual pathogen
C)antibiotic formulations ... specifically killing infected cells
D)antibiotic formulations ... killing bacteria that assist viruses in infecting animal cells
E)nucleoside inhibitors ... inhibiting the replication of the viral genome
B
Emerging viruses can originate from which of the following sources? ( Concept 19.3)
A)animal viruses
B)the mutation of existing human viruses
C)viruses previously confined to small, isolated populations that can now spread due to technological or social changes such as the development of affordable international travel
D)All of the listed responses are correct.
E)None of the listed responses is correct.
D
What is the function of hemagglutinin in the influenza virus? ( Concept 19.3)
A)Hemagglutinin is the name of the reverse transcriptase enzyme in the influenza virus.
B)Hemagglutinin is part of the protein capsid of the influenza virus.
C)Hemagglutinin is the protein that helps the influenza virus attach to host cells.
D)Hemagglutinin is involved in assembling the membrane envelope that the virus uses as a cloak when it leaves an infected cell.
E)Hemagglutinin helps release new viruses from infected cells.
C
Birds act as a natural _____ for the influenza _____ virus.( Concept 19.3)
A)pandemic ... B
B)reservoir ... C
C)buffer ... B
D)defense ... A
E)reservoir ... A
E
Which of the following is an example of vertical transmission of a virus in plants? ( Concept 19.3)
A)Two neighboring plants touch each other, allowing viruses present in one plant to infect the other plant.
B)Viral particles are carried from one plant to another by a pair of pruning shears.
C)Viral particles are carried by the wind from one plant to another.
D)An infected plant produces seeds that contain the virus, giving rise to infected progeny.
E)All of the listed responses are correct.
D
Plant viruses spread throughout the plant by way of _____. ( Concept 19.3)
A)the lymphatic system
B)vertical transmission
C)central vacuoles
D)chloroplasts
E)plasmodesmata
E
Circular RNA molecules that function like a virus in plants are termed _____. ( Concept 19.3)
A)prion
B)rhabdovirus
C)viroid
D)retrovirus
E)None of the listed responses is correct.
C
Prions are _____ that are thought to cause disease by _____. ( Concept 19.3)
A)an abnormal type of capsid ... dramatically enhancing the rate of viral infection
B)RNA molecules ... encoding toxic proteins
C)abnormally shaped proteins ... inducing similar but normally shaped proteins in the brain to adopt the abnormal form
D)DNA molecules ... jumping around the genome and mutating genes
E)mutant DNA molecules ... encoding toxic proteins
C
A new pathogenic form of influenza A can emerge when _____.( Concept 19.3)
A)All of the listed factors likely contribute to the emergence of a new pathogenic strain of influenza A.
B)a virus with a novel genetic makeup recombines with viruses that circulate widely among humans
C)a mutation occurs in a virus as it passes from one host to another
D)the genomes of two or more influenza A strains mix and match during viral assembly within a host
E)there is a concurrent infection of a pig or bird by two or more different strains of influenza A
A
What is the prevailing hypothesis for the surprisingly low infection and mortality rate among people over 64 years of age during the 2009 H1N1 pandemic? ( Concept 19.3)
A)Older people do not breathe as deeply as younger people and therefore fewer viral particles reach the lower lung where infection is most likely to occur.
B)Older people were likely exposed to earlier H1N1 viruses that primed their immune systems for the virus of the 2009 pandemic.
C)A weaker immune system of older people protected them from the hyper-immune response that H1N1 infection triggers in younger people, which led to more pronounced illness and greater likelihood of mortality in the younger age group.
D)The higher overall metabolic rate in younger people provides for greater replication rates of the H1N1 virus, causing a more severe and systemic infection that contributes to a higher mortality rate.
E)Being less active and spending more time indoors, older people had fewer encounters with sick people and fewer opportunities to contract the virus.
B
The avian flu virus H5N1 is considered a greater long-term threat than the swine flu virus H1N1 because _____. ( Concept 19.3)
A)it has a significantly higher mortality rate
B)H5N1 has a greater tendency to become a prophage
C)more people eat chicken meat than pork
D)H5N1 is a DNA virus and the similarity of genome chemistry can promote greater virulence and therefore likelihood of death in humans.
E)it is more readily transmitted between human hosts
A