chapter 19 bio
52.Which of the following human diseases is caused by a virus that requires reverse transcriptase to transcribe its genome inside the host cell?
AIDS
41.What is difference between an epidemic and a pandemic?
An epidemic is restricted to a local region; a pandemic is global.
38.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.
2.What is the function of reverse transcriptase in retroviruses?
It uses viral RNA as a template for DNA synthesis.
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
48.What is the main structural difference between enveloped and nonenveloped viruses?
Enveloped viruses have a phospholipid membrane outside their capsid, whereas nonenveloped viruses do not have a phospholipid membrane.
22.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 nontranslated leader sequence, and then a single long protein-coding region (~7000 nucleotides), followed by a poly-A tail. Observations were made that used radioactive amino acid analogues. 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.
17.Which of the following statements describes the lysogenic cycle of lambda (λ) phage?
The phage genome replicates along with the host genome.
36.How do prions differ from viruses?
Unlike a virus, a prion is a single molecule.Unlike viruses, prions do not include any nucleic acids.Unlike viruses, prions are infectious proteins.
18.Which of the following represents a difference between viruses and viroids?
Viruses have capsids composed of protein, whereas viroids have no capsids.
62.Which of the following supports the argument that viruses are nonliving?
They are not cellular.
50.Why are viruses called obligate intracellular parasites?
They must use a host cell's metabolic enzymes and pathways to obtain energy.They must use a host cell's amino acids to synthesize proteins.They must use a host cell's nucleotides for transcription and replication.They must use a host cell's ribosomes to synthesize proteins.
5.Identify all correct statements about how viroids differ from viruses.
Unlike viruses, viroids do not encode proteins.
10.Why are retroviruses considered a special class of viruses?
They transcribe RNA to DNA using reverse transcriptase.
61.The H1N1 2009 outbreak is considered to have been which of the following?
a pandemic
35.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 a bacteriophage?
control of more than one gene in an operon
57.Which of the following accounts for someone who has had regular herpesvirus-mediated cold sore or genital sore flare-ups?
copies of the herpesvirus genome permanently maintained in host nuclei
34.Which of the following characteristics, structures, or processes is common to both bacteria and viruses?
genetic material composed of nucleic acid
23.Which of the following can be effective in preventing the onset of viral infection in humans?
getting vaccinated
8.If scientists are trying to use what they know about HSV to devise a means of protecting other people from being infected, which of the following would have the best chance of lowering the number of new cases of infection?
interfere with new viral replication in pre existing cases of HSV
7.The virus genome and viral proteins are assembled into virions (virus particles) during _____
the lytic cycle only
15.Emerging viruses arise by
the spread of existing viruses to new host species. the spread of existing viruses more widely within their host species. mutation of existing viruses.
46.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 6300 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?
translation rate
42.Cells were infected with approximately 1000 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 above, how long does it take for virus A to go through one lytic cycle?
45 minutes
47.Cells were infected with approximately 1000 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 above, how long does it take for virus B to go through one lytic cycle?
60 minutes
12.Which of the following is characteristic of the lytic cycle?
A large number of phages are released at a time.
30.Which of the following 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.
25.Why is it ineffective to treat viral disease with antibiotics?
Antibiotics inhibit enzymes specific to bacteria and have no effect on virally encoded enzymes.
19.Why do scientists consider HIV to be an emerging virus?
HIV suddenly became apparent and widespread in the 1980s.
28.Which of the three types of viruses shown above would you expect to include glycoproteins?
I and II only
58.Which of the three types of viruses shown above would you expect to include a capsid(s)?
I, II, and III
39.What happens first when a phage infects a bacterial cell and is going to enter a lysogenic cycle?
Linear DNA circularizes.
37.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.
45.How do prions, which are misfolded proteins, infect organisms?
Prions enter brain cells and cause normal form of the protein to refold into the prion form.
20.Why do RNA viruses appear to have higher rates of mutation?
Replication of their genomes does not involve proofreading.
3.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
33.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. 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 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.
40.If a viral host cell has a mutation that interferes with the addition of carbohydrates to proteins in the Golgi, which of the following could likely result?
The viral envelope proteins would not be glycosylated and might not arrive at the host plasma membrane.
29.Viruses use the host'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 in the host.
6.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.
27.Which of the following viruses would most likely have reverse transcriptase?
an RNA-based lysogenic virus
4.The first class of drugs developed to treat AIDS, such as AZT, were known as reverse transcriptase inhibitors. They worked because they _____.
bonded to the viral reverse transcriptase enzyme, thus preventing the virus from making a DNA copy of its RNA genome
24.A person is most likely to recover from a viral infection if the infected cells _____.
can undergo normal cell division
59.Viral infections in plants _____.
can spread within a plant via plasmodesmata
49.The nucleic acid of a virus particle is enclosed in a protein coat. What is it called?
capsid
54.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. We expect that the plants would _____.
develop the typical symptoms of TMV infection
If you already know that the infectious agent was either a viroid or a prion, which method(s) listed above would allow you to distinguish between these two possibilities?
either I or IV
55.In the figure, at the arrow marked II, what enzyme(s) are being utilized?
host cell DNA polymerase
16.Effective antiviral drugs are usually associated with which of the following properties?
interference with viral replication
13.What are prions?
misfolded versions of normal protein that can cause disease
60.To make a vaccine against mumps, measles, or rabies, which type of viruses would be useful?
negative-sense ssRNA viruses
11.In the figure, when new viruses are being assembled at the point marked IV, what mediates the assembly?
nothing; they self-assemble
21.What do we call a virus that attacks a bacterium?
phage
51.A virus consisting of a single strand of RNA, which is transcribed into complementary DNA, is a _____.
retrovirus
14.Which viruses have single-stranded RNA that acts as a template for DNA synthesis?
retroviruses
43.HIV uses which of the following processes to synthesize a DNA strand using its RNA genome as a template?
reverse transcription
56.Which of the following could use reverse transcriptase to transcribe its genome?
ssRNA
9.A population of viruses with similar characteristics is called a _____.
strain
1. The host range of a virus is determined by _____.
the proteins on its surface and that of the host
32.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
53.Viruses _____.
use the host cell to copy themselves and make viral proteins
44.What is the most effective way to stop viral infections?
vaccines