Deck 33: Viruses

Question 1

Figure 33.1
Cells were infected with approximately 1000 copies of either virus A or virus B at the 0 time point. At 5- 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 Figure 33.1, how long does it take for virus A to go through one lytic cycle?

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

Answer 1

C

Question 2

When people die from HIV infections, it is usually because they

A) divert too much energy toward replicating the virus.
B) have too many T cells, and this overwhelms their immune systems.
C) have too many HIV particles in their lymphatic system, which causes it to shut down.
D) have too few T cells to adequately fight infection.

Answer 2

D

Question 3

What is a significant difference between lytic and lysogenic viral growth?

A) In lysogenic growth, there is a continuous release of mature viral particles throughout the infection.
B) In lysogenic growth, the viral genome gets incorporated into the host genome.
C) In lytic growth, the host cells are not destroyed.
D) In lytic growth, there are no mature viruses produced.

Answer 3

B

Question 4

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?

A) The viral envelope proteins will not be glycosylated and may not arrive at the host plasma membrane.
B) The viral core proteins will not be glycosylated and may not arrive at the host plasma membrane.
C) The viral capsid proteins will not be glycosylated and may not arrive at the host plasma membrane.
D) None of the above will happen.

Question 5

The first class of drugs developed to treat AIDS-such as AZT-were known as reverse transcriptase inhibitors. What was the mechanism by which they worked to treat HIV infections?

A) They bonded to the viral reverse transcriptase enzyme, thus preventing the virus from making a DNA copy of its RNA genome.
B) They bonded to the dsDNA genome of the virus in such a way that it could not separate in order for replication to occur.
C) They targeted and destroyed the viral genome before it could be reverse transcribed into DNA.
D) They prevented host cells from producing the enzymes used by the virus to replicate its genome.

Question 6

What is difference between an epidemic and a pandemic?

A) An epidemic is an actual disease, whereas a pandemic is a worldwide human response to treating that disease.
B) An epidemic is a disease with a fairly low mortality rate, whereas a pandemic has a much higher mortality rate.
C) An epidemic is a disease that is restricted to a small area and does not appear to be spreading or becoming more common, whereas a pandemic is a disease that is spreading wider throughout a population.
D) An epidemic is a disease in a local region that is widening, whereas a pandemic is a disease that is widening to an international scale.

Question 7

You just discovered a new virus. This virus infects heart muscle, where it causes inflammation. This virus has a very high mutation rate. Which of the following is the best strategy for finding a treatment for this virus?

A) Develop a drug that blocks the host's ribosomes, which the virus uses to produce its proteins.
B) Encourage infected individuals to engage in heart- strengthening exercise.
C) Identify the receptor this virus uses and develop an antibody against that receptor.
D) Develop a vaccine from living viruses.

Question 8

Figure 33.1
Which of the following statements applies to lysogeny?

A) Viral proteins are used to replicate the viral genome.
B) The viral genome integrates into the host cell's genome.
C) When the cell divides, the daughter cells are no longer infected.
D) Viral particles are produced continuously.

Question 9

The HIV protease has been the target of several anti- HIV medications. This antiviral strategy is possible because

A) the HIV protease is easily precipitated out of the cell by combining with certain salt solutions.
B) the HIV protease cleaves at specific places in viral polypeptides, which results in the formation of active viral proteins.
C) these drugs are very specific to the active site of the HIV protease.
D) both A and B apply.
E) both B and C apply.

Question 10

What is the main structural difference between enveloped and nonenveloped viruses?

A) Enveloped viruses have their genetic material enclosed by a protein or phospholipid coat.
B) Enveloped viruses have a phospholipid membrane outside their capsid, whereas nonenveloped viruses do not.
C) Nonenveloped viruses have only a phospholipid membrane, while enveloped viruses have two membranes, the other one being a protein capsid.
D) Both viruses have a capsid and phospholipid membrane, but, in the nonenveloped virus, the genetic material is between these two membranes, while in the enveloped virus the genetic material is inside both membranes.

Question 11

Figure 33.1
Using the data in Figure 33.1, how long does it take for virus B to go through one lytic cycle?

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

Question 12

As obligate intracellular parasites, viruses have which of these characteristics?

A) After entering a cell, they use their own protein- synthesizing machinery to make more viral proteins that are used to assemble more copies of themselves.
B) After entering a cell, they use the host cell's machinery to make more copies of themselves using host proteins.
C) After entering a cell, they manufacture their own ATP and carbon- containing compounds, like proteins and nucleic acids, in order to survive.

Question 13

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 do. 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?

A) Viruses can stay in a quiescent state until the host cell evolves this ability.
B) The virus infects only those cells and species that can perform all the replication roles necessary.
C) The virus causes mutations in the human cells, resulting in the formation of new enzymes that are capable of performing these roles.
D) The virus has in its own genome the code for any specialized enzymes that the host does not have.
E) All of the above have been frequently observed.

Question 14

HIV is inactivated in the laboratory after a few minutes of sitting at room temperature; the flu virus is still active after sitting for several hours. What are the practical consequences of these findings?

A) HIV can be transmitted from person to person by sexual contact or injection of infected blood products.
B) The flu virus can be transmitted from person to person by contact with a contaminated surface.
C) The flu virus can be transmitted from person to person by direct physical contact.
D) Both A and B apply.
E) All of the above answers apply.

Question 15

In doing gene therapy, researchers frequently use attenuated viruses. The goal of gene therapy is to insert a normal copy of the mutated, disease- causing gene into the patient's genome, so that they will start producing normal protein. Which type of virus is suited to this application?

A) lytic viruses
B) lysogenic viruses
C) either lytic or lysogenic viruses

Question 16

Does treating a viral infection with antibiotics affect the course of the infection?

A) Yes; antibiotics can prevent viral entry into the cell by binding to host- receptor proteins.
B) Yes; antibiotics activate the immune system, and this decreases the severity of the infection.
C) No; antibiotics do not kill viruses, because viruses use host proteins to replicate and antibiotics affect bacterial proteins.
D) No; antibiotics do not kill viruses, because viruses self- assemble into active particles.

Question 17

Which of the following viruses would be the most likely to have reverse transcriptase?

A) a DNA- based lysogenic virus
B) an RNA- based lysogenic virus
C) an RNA- based lytic virus
D) a DNA- based lytic virus

Question 18

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

A) not show any disease symptoms.
B) develop symptoms typically produced by viroids.
C) develop some but not all of the symptoms of the TMV infection.
D) develop the typical symptoms of TMV infection.
E) become infected, but the sap from these plants would be unable to infect other plants.

Question 19

When HIV infects people, it does not immediately induce AIDS and kill its host. When people die from HIV infections, it is usually because

A) the virus induces a coma and then eventually stops the heart muscle.
B) they have too many T cells, and this overwhelms their immune systems.
C) they have too many HIV particles in their lymph system, which causes it to shut down.
D) the virus starts destroying cells as it divides and causes massive internal hemorrhaging that leads to shock and eventually death.
E) they have too few T cells and become susceptible to secondary infections and cancers.

Question 20

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 nanometres 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?

A) accumulation of new ribosomes
B) transcription rate
C) translation rate
D) formation of new transcription factors
E) replication rate

Question 21

Why do scientists consider HIV to be an emerging virus?

A) HIV mutates so rapidly that the virus of today has very little similarity to the virus in the first AIDS patients from the early 1980s.
B) HIV used to infect only chimps, but it has mutated in such a way that it now infects humans.
C) HIV is now starting to cause diseases other than AIDS, such as rare types of cancers and pneumonias.
D) HIV infected humans long before AIDS first become a problem in the early 1980s, but it has now mutated to a more deadly form.

Question 22

It is believed that HIV has passed from chimps to humans more than once. This is very telling since it suggests that animal- to- human viral transmissions may be more common than previously thought. What is the best evidence in support of the conclusion that HIV made the chimp- to- human leap more than once?

A) HIV has appeared on multiple continents.
B) Human- to- human transmission of HIV requires direct personal contact that simply could not have resulted in the widespread outbreak we see today.
C) Several species are known to have similar viruses resulting in immunodeficiency diseases.
D) HIV has multiple strains, and the virus does not appear to be able to leap from humans back to chimps.

Question 23

Use the following information when answering the corresponding questions).
It has been shown that there are two distinct variants of the HIV virus Bleul et al. 1997. The HIV coreceptors CXCR4 and CCR differentially regulated on human T- lymphocytes. Proceedings of the National Academy of Science 94:1925- 30). One virus preferentially infects macrophages and is called M- tropic. The other preferentially infects T cells and is called T- tropic. The M- tropic viruses use CCR5 and CD4 as coreceptors, and the T- tropic viruses use CXCR4 and CD4 as coreceptors. The
M- tropic viruses are found early in HIV infections; the T- tropic viruses are found late in infections, when AIDS symptoms are prevalent. T- tropic viruses are associated with a drastic decrease in T cells. Macrophages go to the site of wounds, where they are used to fight infections. T cells circulate in the body and fight infections at many sites.
Which receptors for HIV would you expect to find on macrophages and T cells?

A) CXCR4 and CD4 on macrophages; CCR5 and CD4 on T cells
B) CD4 and CXCR4 on macrophages; CXCR4 and CD4 on T cells
C) CCR5 and CD4 on macrophages; CXCR4 and CD4 on T cells
D) CCR5 and CXCR4 on macrophages; CD4 and CXCR4 on T cells

Question 24

Use the following information when answering the corresponding questions).
It has been shown that there are two distinct variants of the HIV virus Bleul et al. 1997. The HIV coreceptors CXCR4 and CCR differentially regulated on human T- lymphocytes. Proceedings of the National Academy of Science 94:1925- 30). One virus preferentially infects macrophages and is called M- tropic. The other preferentially infects T cells and is called T- tropic. The M- tropic viruses use CCR5 and CD4 as coreceptors, and the T- tropic viruses use CXCR4 and CD4 as coreceptors. The
M- tropic viruses are found early in HIV infections; the T- tropic viruses are found late in infections, when AIDS symptoms are prevalent. T- tropic viruses are associated with a drastic decrease in T cells. Macrophages go to the site of wounds, where they are used to fight infections. T cells circulate in the body and fight infections at many sites.
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 results in labelling of only very long proteins, while longer periods of labelling result in several different short polypeptides. What conclusion is most consistent with the results of the radioactive labelling experiment?

A) The RNA is translated into short polypeptides, which are subsequently assembled into large ones.
B) The large radioactive polypeptides are coded by the host, whereas the short ones are coded for by the virus.
C) The RNA is only translated into a single long polypeptide, which is then cleaved into shorter ones.
D) Host- cell ribosomes only translate the viral code into short polypeptides.

Question 25

You have isolated the genome from a novel virus and would like to determine its composition. You have three tu each containing one of these substances:
1) a protein that degrades dsDNA DNase, tube 1)
2) a protein that degrades ssRNA RNase, tube 2)
3) a protease that degrades viral proteins tube 3)
You add some of your novel genome to tubes 1, 2, and 3. The genome is degraded in tube 2, but not in tube 1 or t
3) Based on your knowledge of genome types that have been found in viruses, what could the genome's composition be?

A) ssDNA
B) ssRNA
C) dsDNA
D) protein
E) None of the above seem likely.

Question 26

Use the following information when answering the corresponding questions).
It has been shown that there are two distinct variants of the HIV virus Bleul et al. 1997. The HIV coreceptors CXCR4 and CCR differentially regulated on human T- lymphocytes. Proceedings of the National Academy of Science 94:1925- 30). One virus preferentially infects macrophages and is called M- tropic. The other preferentially infects T cells and is called T- tropic. The M- tropic viruses use CCR5 and CD4 as coreceptors, and the T- tropic viruses use CXCR4 and CD4 as coreceptors. The
M- tropic viruses are found early in HIV infections; the T- tropic viruses are found late in infections, when AIDS symptoms are prevalent. T- tropic viruses are associated with a drastic decrease in T cells. Macrophages go to the site of wounds, where they are used to fight infections. T cells circulate in the body and fight infections at many sites.
What would the result be if a drug that blocks the action of RNA polymerase was introduced into a virus- infected organism?

A) The newly formed virions virus particles) would be unable to leave the host cell.
B) The viral proteins would not be made, and the virus would not be able to reproduce.
C) Viral proteins and viral DNA particles would not be able to assemble.
D) The virus would not be able to enter new host cells.

Question 27

Which of the following is a reason why viruses are considered non- living?

A) They contain different nucleotides in their DNA and RNA.
B) They do not have ribosomes or tRNAs.
C) They are surrounded by polysaccharides.
D) They do not contain a nuclear membrane.

Question 28

Which of the following viruses would have a disrupted replication cycle if their reverse- transcriptase enzyme was non- functional?

A) double- stranded RNA viruses
B) retroviruses
C) positive- sense single- stranded RNA viruses
D) negative- sense single- stranded RNA viruses
E) double- stranded DNA viruses

Question 29

Which of the following is true regarding the ambi- sense virus?

A) The base sequences in the genome are complementary to those in viral mRNAs.
B) The genome contains the same sequences as the mRNA required to produce viral proteins.
C) Some sections of the genome are positive, while others are negative- sense.

Question 30

You have isolated a newly discovered virus and are attempting to characterize it. You begin with its genome. You first isolate the virion- producing mRNA from culture cells infected with the virus. When you compare these mRNA with the viral genome, you find that they are complementary. What does this tell you?

A) This virus has a negative- sense genome.
B) This virus has an ambisense genome.
C) The data are inconclusive.
D) This virus has a positive- sense genome.

Question 31

Which of the following is the most important reason that developing treatments and vaccines, as well as staging an effective immune response for HIV infections, has been so difficult compared with other viruses?

A) The virus has few, if any, replication- correcting enzymes, and consequently mutates at a high rate.
B) Researchers probably have not yet identified the actual cause of AIDS and, thus, cannot target their drug development accordingly.
C) The virus has no recognizable antigens and, thus, cannot be identified easily by the host's immune system.
D) The virus evades the immune system and drugs by hiding inside cells of the immune system, such as helper T cells.

Question 32

Which of the following plays an important role in the ability of an enveloped virus to fuse with the host cell?

A) Presence of capsid protein shell on the outermost layer of the virus.
B) Presence of the same phospholipid bilayer structure in both virus and host cell.
C) Presence of antibodies on the host cell surface that recognize the virus.
D) Answers A and B

Question 33

You have isolated the genome from a novel virus and would like to determine its composition. You have three tu each containing one of these substances:
1) a protein that degrades dsDNA DNase, tube 1)
2) a protein that degrades ssRNA RNase, tube 2)
3) a protein that degrades other proteins protease, tube 3)
You add some of your novel genome to tubes 1, 2, and 3. The genome is not degraded in tube 1, 2, or 3. Based on your knowledge of genome types that have been found in viruses, what could the genome's composition be?

A) dsDNA that is resistant to DNase
B) dsRNA
C) ssDNA
D) It could be any of the above.

Question 34

To make a vaccine against mumps, measles, or rabies, which type of viruses would be useful?

A) positive- sense ssRNA viruses
B) dsRNA viruses
C) retroviruses
D) negative- sense ssRNA viruses
E) dsDNA viruses

Question 35

You are a physician, and you suspect your patient has a viral infection that has never been seen in humans. The infection is localized in the cells along the lining of the small intestine. The cells in this area are regularly sloughed off and replaced with new cells; that is, these cells are constantly dividing. When you isolate this new virus and incubate it in culture, you discover that it does not replicate well in cultures that have slowly dividing cells, but it does much more damage in cultures that have actively dividing cells. What do these findings suggest about this new virus?

A) It is a double- stranded DNA virus.
B) It is a double- stranded RNA virus.
C) It is a negative- sense, single- stranded RNA virus.
D) It is a single- stranded DNA virus.