Chapter 19 MasteringBiology Homework
The best flu vaccine would work to prevent people from which of the following?
Influenza A, B, and C
Classify each phrase as applying to the lytic cycle, the lysogenic cycle, or both types of reproductive cycles of phages.
Lytic Cycle- the cell is lysed (broken open), new phages are assembled from viral DNA ad proteins, the host is destroyed Lysogenic Cycle- the cell reproduces normally, the viral DNA integrates into the chromosome of the host cell Both Cycles- viral genes are replicated
Why is combination drug therapy for HIV/AIDS less likely to lead to resistance than single drug therapy?
The likelihood of one virus spontaneously mutating to be resistant to several different drugs at the same time is extremely small.
Emerging viruses arise by
-the spread of existing viruses to new host species. -mutation of existing viruses. -the spread of existing viruses more widely within their host species.
Which of the following characteristics, structures, or processes is common to both bacteria and viruses?
genetic material composed of nucleic acid
The pointer is indicating the virus's _____.
genome
Viruses are
not alive because they are not made of cells and require a host cell for reproduction.
You are an immunologist working on a new flu vaccine that attacks molecules with the same basic make-up as hemagglutinin. What is your area of expertise?
proteins
Click on the diagram to start the animation. What enzyme is responsible for the process seen here?
reverse transcriptase
HIV uses which of the following processes to synthesize a DNA strand using its RNA genome as a template?
reverse transcription
The genetic material of HIV consists of _____.
single-stranded RNA
Viruses _____.
use the host cell to copy themselves and make viral proteins
What is the most effective way to stop viral infections?
vaccines
31) Antiviral drugs that have become useful are usually associated with which of the following properties? A) ability to remove all viruses from the infected host B) interference with the viral reproduction C) prevention of the host from becoming infected D) removal of viral proteins E) removal of viral mRNAs
B) interference with the viral reproduction
24) If you already knew that the infectious agent was either bacterial or viral, which treatment would allow you to distinguish between these two possibilities? A) I B) II C) III D) IV E) either II or IV
C) III
13) In many ways, the regulation of the genes of a particular group of viruses will be similar to the regulation of the host genes. Therefore, which of the following would you expect of the genes of the bacteriophage? A) regulation via acetylation of histones B) positive control mechanisms rather than negative C) control of more than one gene in an operon D) reliance on transcription activators E) utilization of eukaryotic polymerases
C) control of more than one gene in an operon
15) Which of the following terms describes bacteriophage DNA that has become integrated into the host cell chromosome? A) intemperate bacteriophages B) transposons C) prophages D) T-even phages E) plasmids
C) prophages
9) Based on the above table, which virus meets the Baltimore requirements for a retrovirus?
D
Which group of variants was the earliest to cause H1N1 flu in over 100 patients in Taiwan?
Group 7 (black line)
Which statements about viruses are true? Select the four statements that are true.
-Enveloped viruses bud from the host cell. -A retrovirus contains RNA. -HIV contains reverse transcriptase. -The capsid enters the host cell if the virus is enveloped.
Which of these is the viral genome?
E
Which of the following can be found in bacteria, but not viruses?
a cell membrane
The H1N1 2009 outbreak is considered to have been which of the following?
a pandemic
The nucleic acid of a virus particle is enclosed in a protein coat. What is it called?
capsid
Which of the following is NOT a characteristic of living things?
creating energy
Cycle A is the _____ cycle and cycle B is the _____ cycle.
lytic ... lysogenic
Double-stranded viral DNA is incorporated into a host cell as a _____.
provirus
27) Which of the following represents a difference between viruses and viroids? A) Viruses infect many types of cells, whereas viroids infect only prokaryotic cells. B) Viruses have capsids composed of protein, whereas viroids have no capsids. C) Viruses contain introns; viroids have only exons. D) Viruses always have genomes composed of DNA, whereas viroids always have genomes composed of RNA. E) Viruses cannot pass through plasmodesmata; viroids can.
B) Viruses have capsids composed of protein, whereas viroids have no capsids
What is the source of a viral envelope?
host cell membrane
What do we call a virus that attacks a bacterium?
phage
The lytic cycle of bacteriophage infection ends with the _____.
rupture of the bacterium
10) Based on the above table, which virus meets the requirements for a bacteriophage?
A
How do prions differ from viruses?
-Unlike a virus, a prion is a single molecule. -Unlike viruses, prions are infectious proteins. -Unlike viruses, prions do not include any nucleic acids.
Referring to the phylogenetic tree in Figure 1, which variant is more closely related to A/Taiwan1018/2011 in group 9 (brown): A/Taiwan/552/2011 or A/Taiwan/8542/2009? (For help reading the phylogenetic tree, see the hint.)
A/Taiwan/552/2011; variants 1018/2011 and 552/2011 share a more recent common ancestor than is shared with variant 8542/2009.
11) A linear piece of viral DNA of 8 kb can be cut with either of two restriction enzymes (X and Y). These are subjected to electrophoresis and produce the following bands: Cutting the same 8 kb piece with both enzymes together results in bands at 4.0, 2.5, 1.0, and 0.5. Of the possible arrangements of the sites given below, which one is most likely?
B
1) What characteristics of electron microscopes make them most useful for studying viruses? A) high energy electrons with high penetrance B) requirement that specimens be viewed in a vacuum C) necessity for specimens to be dry and fixed qE) use of magnetic fields to focus electrons
D) shorter wavelengths providing higher resolution
What is the function of reverse transcriptase in retroviruses?
It uses viral RNA as a template for DNA synthesis.
Do all of the groups have the same number of branches or branch tips? What does this result indicate?
No; some groups experienced a higher mutation rate than others.
What kind of cell can recognize infected cells and kill them directly?
T cells
Which of the following supports the argument that viruses are nonliving?
They are not cellular.
Identify all correct statements about how viroids differ from viruses.
Unlike viruses, the genetic material of a viroid is protein.
Effective antiviral drugs are usually associated with which of the following properties?
interference with viral replication
A disease that spreads rapidly around the world is called a(n) ___________.
pandemic
Viral DNA makes mRNA by the process of _____.
transcription
Refer to the treatments listed below to answer the following questions. You isolate an infectious substance that is capable of causing disease in plants, but you do not know whether the infectious agent is a bacterium, virus, viroid, or prion. You have four methods at your disposal that you can use to analyze the substance in order to determine the nature of the infectious agent. I. treating the substance with nucleases that destroy all nucleic acids and then determining whether it is still infectious II. filtering the substance to remove all elements smaller than what can be easily seen under a light microscope III. culturing the substance by itself on nutritive medium, away from any plant cells IV. treating the sample with proteases that digest all proteins and then determining whether it is still infectious 23) Which treatment could definitively determine whether or not the component is a viroid? A) I B) II C) III D) IV E) first II and then III
A) I
5) Why are viruses referred to as obligate parasites? A) They cannot reproduce outside of a host cell. B) Viral DNA always inserts itself into host DNA. C) They invariably kill any cell they infect. D) They can incorporate nucleic acids from other viruses. E) They must use enzymes encoded by the virus itself.
A) They cannot reproduce outside of a host cell
30) Which of the following is the best predictor of how much damage a virus causes? A) ability of the infected cell to undergo normal cell division B) ability of the infected cell to carry on translation C) whether the infected cell produces viral protein D) whether the viral mRNA can be transcribed E) how much toxin the virus produces
A) ability of the infected cell to undergo normal cell division
7) Most human-infecting viruses are maintained in the human population only. However, a zoonosis is a disease that is transmitted from other vertebrates to humans, at least sporadically, without requiring viral mutation. Which of the following is the best example of a zoonosis? A) rabies B) herpesvirus C) smallpox D) HIV E) hepatitis virus
A) rabies
20) What is the name given to viruses that are single-stranded RNA that acts as a template for DNA synthesis? A) retroviruses B) proviruses C) viroids D) bacteriophages E) lytic phages
A) retroviruses
4) The host range of a virus is determined by A) the proteins on its surface and that of the host. B) whether its nucleic acid is DNA or RNA. C) the proteins in the host's cytoplasm. D) the enzymes produced by the virus before it infects the cell. E) the enzymes carried by the virus.
A) the proteins on its surface and that of the host.
A new disease emerges and exists only as a free-floating virus. Which of the following will make antibodies against this?
B cells
21) What is the function of reverse transcriptase in retroviruses? A) It hydrolyzes the host cell's DNA. B) It uses viral RNA as a template for DNA synthesis. C) It converts host cell RNA into viral DNA. D) It translates viral RNA into proteins. E) It uses viral RNA as a template for making complementary RNA strands.
B) It uses viral RNA as a template for DNA synthesis.
17) Why do RNA viruses appear to have higher rates of mutation? A) RNA nucleotides are more unstable than DNA nucleotides. B) Replication of their genomes does not involve the proofreading steps of DNA replication. C) RNA viruses replicate faster. D) RNA viruses can incorporate a variety of nonstandard bases. E) RNA viruses are more sensitive to mutagens.
B) Replication of their genomes does not involve the proofreading steps of DNA replication.
26) Which of the following describes plant virus infections? A) They can be controlled by the use of antibiotics. B) They are spread throughout a plant by passing through the plasmodesmata. C) They have little effect on plant growth. D) They are seldom spread by insects. E) They can never be inherited from a parent.
B) They are spread throughout a plant by passing through the plasmodesmata.
3) Viral envelopes can best be analyzed with which of the following techniques? A) transmission electron microscopy B) antibodies against specific proteins not found in the host membranes C) staining and visualization with the light microscope D) use of plaque assays for quantitative measurement of viral titer E) immunofluorescent tagging of capsid proteins
B) antibodies against specific proteins not found in the host membranes
Which of these is reverse transcriptase?
C
16) Which of the following statements describes the lysogenic cycle of lambda (_) phage? A) After infection, the viral genes immediately turn the host cell into a lambda-producing factory, and the host cell then lyses. B) Most of the prophage genes are activated by the product of a particular prophage gene. C) The phage genome replicates along with the host genome. D) Certain environmental triggers can cause the phage to exit the host genome, switching from the lytic to the lysogenic. E) The phage DNA is incorporated by crossing over into any nonspecific site on the host cell's DNA.
C) The phage genome replicates along with the host genome
19) A researcher lyses a cell that contains nucleic acid molecules and capsomeres of tobacco mosaic virus (TMV). The cell contents are left in a covered test tube overnight. The next day this mixture is sprayed on tobacco plants. Which of the following would be expected to occur? A) The plants would develop some but not all of the symptoms of the TMV infection. B) The plants would develop symptoms typically produced by viroids. C) The plants would develop the typical symptoms of TMV infection. D) The plants would not show any disease symptoms. E) The plants would become infected, but the sap from these plants would be unable to infect other plants.
C) The plants would develop the typical symptoms of TMV infection.
14) Which of the following is characteristic of the lytic cycle? A) Many bacterial cells containing viral DNA are produced. B) Viral DNA is incorporated into the host genome. C) The viral genome replicates without destroying the host. D) A large number of phages is released at a time. E) The virus-host relationship usually lasts for generations.
D) A large number of phages is released at a time.
25) Which treatment would you use to determine if the agent is a prion? A) I only B) II only C) III only D) IV only E) either I or IV
D) IV only
12) Which of the following accounts for someone who has had a herpesvirus-mediated cold sore or genital sore getting flare-ups for the rest of life? A) re-infection by a closely related herpesvirus of a different strain B) re-infection by the same herpesvirus strain C) co-infection with an unrelated virus that causes the same symptoms D) copies of the herpesvirus genome permanently maintained in host nuclei E) copies of the herpesvirus genome permanently maintained in host cell cytoplasm
D) copies of the herpesvirus genome permanently maintained in host nuclei
2) Viral genomes vary greatly in size and may include from four genes to several hundred genes. Which of the following viral features is most apt to correlate with the size of the genome? A) size of the viral capsomeres B) RNA versus DNA genome C) double versus single strand genomes D) size and shape of the capsid E) glycoproteins of the envelope
D) size and shape of the capsid
33) Which of the following is the most probable fate of a newly emerging virus that causes high mortality in its host? A) It is able to spread to a large number of new hosts quickly because the new hosts have no immunological memory of them. B) The new virus replicates quickly and undergoes rapid adaptation to a series of divergent hosts. C) A change in environmental conditions such as weather patterns quickly forces the new virus to invade new areas. D) Sporadic outbreaks will be followed almost immediately by a widespread pandemic. E) The newly emerging virus will die out rather quickly or will mutate to be far less lethal.
E) The newly emerging virus will die out rather quickly or will mutate to be far less lethal.
Once a group of variants had a peak number of infections, did members of that same group cause another wave of infection?
No, each group of variants caused only one wave of infection.
As a result of the lytic cycle, _____.
the host cell's DNA is destroyed
Why is it ineffective to treat viral disease with antibiotics?
Antibiotics inhibit enzymes specific to bacteria and have no effect on virally encoded enzymes.
Which of the following represents a difference between viruses and viroids?
Viruses have capsids composed of protein, whereas viroids have no capsids.
Homeostasis is a living organism's
ability to maintain constant internal conditions even when environmental conditions change.
Which of these binds to receptor molecules on the host cell membrane?
A
Which of the following is characteristic of the lytic cycle?
A large number of phages are released at a time.
22) Which of the following can be effective in preventing viral infection in humans? A) getting vaccinated B) taking nucleoside analogs that inhibit transcription C) taking antibiotics D) applying antiseptics E) taking vitamins
A) getting vaccinated
6) Which of the following molecules make up the viral envelope? A) glycoproteins B) proteosugars C) carbopeptides D) peptidocarbs E) carboproteins
A) glycoproteins
All of the statements below are true. Select the statement that best supports the view of most biologists that viruses are nonliving.
An isolated virus is unable to replicate its genes or regenerate ATP.
Use the following information to answer the following questions. In 1971, David Baltimore described a scheme for classifying viruses based on how the virus produces mRNA. The table below shows the results of testing five viruses for nuclease specificity, the ability of the virus to act as an mRNA, and presence (+) or absence (-) of its own viral polymerase. Virus Nuclease Sensitivity Genome as mRNA Polymerase A Dnase - - B Rnase + - C Dnase - + D Rnase - + E Rnase + - 8) Given Baltimore's scheme, a positive sense single-stranded RNA virus such as the polio virus would be most closely related to which of the following? A) T-series bacteriophages B) retroviruses that require a DNA intermediate C) single-stranded DNA viruses such as herpesviruses D) nonenveloped double-stranded RNA viruses E) linear double-stranded DNA viruses such as adenovirus
B) retroviruses that require a DNA intermediate
32) Which of the following series best reflects what we know about how the flu virus moves between species? A) An avian flu virus undergoes several mutations and rearrangements such that it is able to be transmitted to other birds and then to humans. B) The flu virus in a pig is mutated and replicated in alternate arrangements so that humans who eat the pig products can be infected. C) A flu virus from a human epidemic or pandemic infects birds; the birds replicate the virus differently and then pass it back to humans. D) An influenza virus gains new sequences of DNA from another virus, such as a herpesvirus; this enables it to be transmitted to a human host. E) An animal such as a pig is infected with more than one virus, genetic recombination occurs, the new virus mutates and is passed to a new species such as a bird, the virus mutates and can be transmitted to humans.
E) An animal such as a pig is infected with more than one virus, genetic recombination occurs, the new virus mutates and is passed to a new species such as a bird, the virus mutates and can be transmitted to humans.
18) Most molecular biologists think that viruses originated from fragments of cellular nucleic acid. Which of the following observations supports this theory? A) Viruses contain either DNA or RNA. B) Viruses are enclosed in protein capsids rather than plasma membranes. C) Viruses can reproduce only inside host cells. D) Viruses can infect both prokaryotic and eukaryotic cells. E) Viral genomes are usually more similar to the genome of the host cell than to the genomes of viruses that infect other cell types.
E) Viral genomes are usually more similar to the genome of the host cell than to the genomes of viruses that infect other cell types.
How do prions, which are misfolded proteins, infect organisms?
Prions enter brain cells and cause normal forms of the protein to refold into the prion form.
A plant that has been raised in a sterile environment shows symptoms of a viral infection. How would you explain this?
The viral infection was acquired by vertical transmission.
Sort the items according to whether they may be found only in free virus particles, only in uninfected host cells, or in both viruses and host cells.
Viruses only- Capsid, Capsomere (core protein), Envelope with glycoproteins Host cell only- Ribosome Both- Protein, RNA, DNA
How does a virus differ from a bacterium?
Viruses, unlike bacteria, lack metabolic enzymes.
In the lysogenic cycle _____.
viral DNA is replicated along with host DNA
The pointer is indicating the _____.
viral protein coat
29) What are prions? A) misfolded versions of normal brain protein B) tiny molecules of RNA that infect plants C) viral DNA that has had to attach itself to the host genome D) viruses that invade bacteria E) a mobile segment of DNA
A) misfolded versions of normal brain protein
28) The difference between vertical and horizontal transmission of plant viruses is that A) vertical transmission is transmission of a virus from a parent plant to its progeny, and horizontal transmission is one plant spreading the virus to another plant. B) vertical transmission is the spread of viruses from upper leaves to lower leaves of the plant, and horizontal transmission is the spread of a virus among leaves at the same general level.
A) vertical transmission is transmission of a virus from a parent plant to its progeny, and horizontal transmission is one plant spreading the virus to another plant.
What is the function of reverse transcriptase?
It catalyzes the formation of DNA from an RNA template.
Which of the following statements describes the lysogenic cycle of lambda (λ) phage?
The phage genome replicates along with the host genome.
Which of the following statements about viruses is FALSE?
The widespread use of antibiotics has led to resistant strains of viruses.
Groups 9, 10, and 11 all had H1N1 variants that caused a large number of infections at the same time in Taiwan. Does this mean that the scientists' hypothesis, that new variants cause new waves of infection, was incorrect? Explain your answer.
Their hypothesis was still supported; these three groups arose along different lineages but emerged to cause illness during the same wave.
One variant in the green groups (Groups 1, 3, and 6) was used to make a vaccine that was distributed very early in the pandemic. Based on the graphed data, does it look like the vaccine was effective? Why or why not?
Yes, it was effective; the green line never reaches 100 on the y-axis.
Suppose you were in charge of sending an unmanned space probe to a new planet in search of life. The probe would be able to collect and test samples and make observations, but the planet is too far away for the probe to be able to bring samples back to Earth. The probe is small and would only be able to run a few tests, so you want to pick a test for evidence of life that is broad enough to incorporate all forms of life as we know it. Which one of the following tests would be the best to use in this situation?
a test for the presence of cells that contain DNA
What are prions?
misfolded versions of normal protein that can cause disease
