Chapter 19 Review
Which of the following human diseases is caused by a virus that requires reverse transcriptase to transcribe its genome inside the host cell?
AIDS
Which of the following statements best reflects what we know about how the flu virus moves between species?
An animal such as a pig is infected with more than one virus, genetic recombination occurs, the new virus mutates, the virus is passed to a new species such as a bird, and the virus mutates again and can now be transmitted to humans.
What is difference between an epidemic and a pandemic?
An epidemic is restricted to a local region; a pandemic is global.
To cause a human pandemic, the H5N1 avian flu virus would have to ____________________.
Become capable of human-to-human transmission
What is the function of reverse transcriptase in retroviruses?
It uses viral RNA as a template for DNA synthesis.
Which of the following processes can be effective in preventing the onset of viral infection in humans?
Getting vaccinated to certain viruses.
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?
The cells can undergo normal cell division.
Which of the following statements accurately describes the lysogenic cycle of lambda (λ) phage?
The phage genome is integrated into the host chromosome where it is replicated along with the host genome.
The host range of a virus is determined by ________.
The proteins on its surface and that of the host.
Viruses use the host cell's machinery to make copies of themselves. However, some human viruses require a type of replication that humans do not normally have. For example, humans normally do not have the ability to convert RNA into DNA. How can these types of viruses infect humans, when human cells cannot perform a particular role that the virus requires?
The viral genome codes for specialized enzymes not found in the host cells.
If a viral host cell has a mutation that interferes with the addition of carbohydrates to proteins in the Golgi apparatus, which of the following processes could likely result?
The viral envelope proteins would not have glycoproteins added to them and might not arrive at the host plasma membrane.
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. What would you expect to happen to the plants that were sprayed with the mixture?
The plants would develop the typical symptoms of TMV infection.
Which of the following statements correctly describes vaccines and how they help prevent viral infection?
Vaccines are inactive versions of a virus that stimulate an immune reaction in a person.
Which of the following descriptions correctly identifies the main structural differences between viruses with envelopes and viruses without envelopes?
Viruses with envelopes have a phospholipid membrane outside their capsid, whereas viruses without envelopes do not have a phospholipid membrane.
Evidence suggests that factors that contribute towards the virulence of E. coli strain O157:H7, a bacterial strain reported to cause several food poisoning deaths, are 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 the strain from harmless E. coli strains, such as those that reside in our intestines?
The virus infected the bacterium, and allowed the bacterial population to replicate with a copy of the phage genome in each new bacterium.
Which of the following statements is correct regarding viral infections in plants?
They can spread within a plant via plasmodesmata.
Which of the following processes can viruses carry out?
They can use the host cell to copy themselves and make viral proteins.
A population of viruses with similar characteristics is called a ________.
class
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 host species. D) all of the above
all of the above
RNA viruses require their own supply of certain enzymes because _________________.
host cells lack enzymes that can replicate the viral genome.
The virus genome and viral proteins are assembled into virus particles during which of the following parts of the reproductive cycle?
the lytic cycle only
The difference between vertical and horizontal transmission of plant viruses is that 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.
Use the following figure and information to answer the question(s) 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. The intact cells were removed from the sample, and the number of viruses per milliliter of culture was determined. Using the data in the figure, how long does it take for virus A to go through one lytic cycle?
45 minutes
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. The intact cells were removed from the sample, and the number of viruses per milliliter of culture was determined. Using the data in the figure, how long does it take for virus B to go through one lytic cycle?
60 minutes
Which of the following characteristics is typical of the lytic cycle of a bacteriophage?
A large number of phages are released at a time.
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 regulation mechanisms would you expect of the genes of a bacteriophage?
Control of more than one gene in an operon
Which of the following events or characteristics accounts for someone who has had regular herpesvirus-mediated cold sores or genital sore flare-ups?
Copies of the herpesvirus genome permanently maintained the host nuclei.
Which of the following characteristics, structures, or processes is common to both bacteria and viruses?
Genetic material composed of nucleic acid
Why do scientists consider HIV to be an emerging virus?
HIV suddenly became apparent and widespread in the 1980s.
Which of the following processes within viral replication is the greatest source of genetic variation in RNA virus populations?
High mutation rate due to lack of proofreading of RNA genome replication errors.
Use the figure to answer the question. In the figure, at the arrow marked II, what enzyme is being utilized?
Host cell DNA polymerase
You isolate an infectious substance capable of causing disease in plants, but you do not know whether the infectious agent is a bacterium, virus, or prion. You have four methods at your disposal to analyze the substance and determine the nature of the infectious agent. I. Treat the substance with enzymes that destroy all nucleic acids, and then determine whether the substance is still infectious. II. Filter the substance to remove all elements smaller than what can be easily seen under a light microscope. III. Culture the substance on nutritive medium, away from any plant cells. IV. Treat the sample with proteases that digest all proteins, and then determine whether the substance is still infectious. If you already know that the infectious agent was either a virus or a prion, which method(s) listed above would allow you to distinguish between these two possibilities?
I only
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)?
I, II, and III
Use the figures to answer the question. Which of the three types of viruses shown would you expect to include glycoproteins?
II only
You isolate an infectious substance capable of causing disease in plants, but you do not know whether the infectious agent is a bacterium, virus, or prion. You have four methods at your disposal to analyze the substance and determine the nature of the infectious agent. I. Treat the substance with enzymes that destroy all nucleic acids and then determine whether the substance is still infectious. II. Filter the substance to remove all elements smaller than what can be easily seen under a light microscope. III.Culture the substance on a nutritive medium, away from any plant cells. IV.Treat the sample with proteases that digest all proteins, and then determine whether the substance is still infectious. If you already know that the infectious agent was either bacterial or viral, which method(s) listed above would allow you to distinguish between these two possibilities?
II or III
The herpes viruses are important 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 three 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 again, and infect others. If scientists are trying to use what they know about the herpes simplex virus to devise a means of protecting other people from being infected, which of the following treatments would have the best chance of lowering the number of new cases of infection?
Interfere with new viral replication in preexisting cases of herpes simplex virus.
Effective antiviral drugs are usually associated with which of the following properties?
Interference with viral replication.
Use the figure to answer the question. In the figure, when new viruses are being assembled at the point marked IV, what mediates the assembly?
No mediator is required; the new viruses self-assemble
Will treating a viral infection with antibiotics affect the course of the infection?
No; antibiotics work by inhibiting enzymes specific to bacteria. Antibiotics have no effect on eukaryotic or virally encoded enzymes.
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 breeding ground 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 of why this virus contained sequences from bird, pig, and human viruses?
Related viruses can undergo genetic recombination if the RNA genomes mix and match during viral assembly.
Why do RNA viruses appear to have higher rates of mutation?
Replication of their genomes does not involve proofreading.
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 ____________.
T4 protein and T4 DNA
Poliovirus is an RNA virus of the picornavirus group, which uses its RNA as mRNA. At its 5′ end, the RNA genome has a viral protein (VPg) instead of a 5′ 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. Observations were made that used radioactive amino acids similar in structure to those that are found in viruses and other organisms. Short-period use of the radioactive amino acids result in labeling of only very long proteins, while longer periods of labeling result in several different short polypeptides. What conclusion is most consistent with the results of the radioactive labeling experiment?
The RNA is only translated into a single long polypeptide, which is then cleaved into shorter ones.
The first class of antiviral drugs developed to treat HIV infection, such as AZT, were known as reverse transcriptase inhibitors. How did these drugs carry out their functions?
The drug molecules bonded to the viral reverse transcriptase enzyme, thus preventing the virus from making a DNA copy of its RNA genome.
HIV is inactivated in the laboratory after a few minutes of sitting at room temperature, but the flu virus is still active after sitting for several hours. What are the practical consequences of these findings?
The flu virus can be transmitted more easily from person to person than HIV.
The herpesviruses are important 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 three 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 again, and infect others. In electron micrographs of HSV infection, it can be seen that the intact virus initially reacts with cell-surface proteoglycans, then with specific receptors. This is later followed by viral capsids docking with nuclear pores. Afterward, the capsids go from being full to being "empty." Which of the following statements best fits these observations?
The viral envelope mediates entry into the cell, the capsid mediates entry into the nuclear membrane, and the genome is all that enters the nucleus.
Which of the following statements supports the argument that viruses are nonliving?
They do not carry out metabolic processes.
Which of the following characteristics correctly describes retroviruses?
They have a single-stranded RNA that acts as a template for DNA synthesis.
Some viruses can be crystallized and their structures analyzed. One such virus is yellow mottle virus, which infects beans. This virus has a single-stranded RNA genome containing about 6,300 nucleotides. Its capsid is 25-30 nm in diameter and contains 180 identical capsomeres. If the yellow mottle virus begins its infection of a cell by using its genome as mRNA, which of the following would you expect to be able to measure when analyzing the reproduction of this virus?
Translation rate
Which of the following statements correctly describes a difference between viruses and prions?
Viruses generally cause disease symptoms quickly, whereas prions generally take many years to cause disease symptoms.
Which of the following viruses would most likely have reverse transcriptase inside them?
an RNA-based lysogenic virus
What are prions?
misfolded versions of normal protein that can cause disease
A virus consisting of a single strand of RNA, which is reverse transcribed into complementary DNA, is referred to as a ________.
retrovirus
Which of the following types of viral genomes could be transcribed using reverse transcriptase?
ssRNA