Questions For Chapter 15

1 What features of the viral replication cycle are shared by measles virus, vesicular stomatitis virus, and influenza virus?

2 When the genomes of negative-sense RNA viruses are purified and introduced into cells that are permissive to the original intact virus, what will occur?

3 The Rhabdoviridae are typical negative-sense RNA viruses and must carry out two types of RNA synthesis during infection: transcription and replication. Briefly describe each of these modes of viral RNA synthesis.

4 Sin Nombre virus is the causative agent of the outbreak of hantavirus-associated disease that was first identified in a cluster of cases originating in the Four Corners area of the southwestern United States.

  • a) To which virus family does this virus belong?
  • b) Which animal is the vector for transmission of this virus to humans?
  • a) Which of these features justify inclusion of SpFV in the Orthomyxoviridae family?
  • b) Which of these features justify your proposal that SpFV should be considered a new genus of this family?
  • c) What feature of the disease caused by this virus makes it different from other members of its genus?

5 Bunyavirus gene expression includes three different solutions to the problem of presenting the host cell with a "monocistronic" mRNA. For each of the genome segments (L, M, and S), describe in a simple drawing or in one sentence how this problem is solved.

6 Your laboratory has now become the world leader in research on the spring fever virus (SpFV), especially the debilitating variant SpFV-4 that causes senioritis. Your team has determined that these viruses are members of the family Orthomyxoviridae, but an international commission on virus nomenclature has suggested that they be assigned to a subgenus of the influenza viruses. While you agree with the family designation, you are convinced that they belong to a new genus that you have tentatively called the Procrastinoviruses.

The following table list properties of SpFV strains that your laboratory has investigated.

You have just received an isolate of SpFV-4 obtained from a severe outbreak of senioritis at a large East Coast university. The epidemic began among a group of students who had just returned from a semester abroad in Paris.

Viral function

Results for SpFV

A

Virion membrane glycoproteins

Two major proteins, one with hemagglutinin activity and the other with neuraminidase activity

B

Matrix proteins in virion

One matrix protein

C

Genome segments

Eight single-stranded RNA molecules

D

Viral mRNA synthesis

Nuclear location, with cap scavenging from host mRNA precursors and RNA splicing to produce some species of viral mRNA

E

Nonstructural (NS) proteins in infected cells

Three NS proteins, two encoded by RNA segment 8 and one encoded by RNA segment 6

F

Site of infection

Generalized neuromuscular locations, ultimately targeting higher neural functions associated with and memory motivation

  • c) As an expert virologist, which viral proteins do you predict are most likely to distinguish this isolate of SpFV-4 from those you have investigated in your laboratory?
  • d) What phenomenon could account for these differences?

7 What are two differences between the members of the Hantavirus genus and members of the other genera of the family Bunyaviridae?

8 Influenza virus will not grow in a cell from which the nucleus has been removed. Although influenza virus does not have a DNA intermediate in its life cycle, there is still a requirement for nuclear functions.

  • a) In isolates of influenza virus H and N numbers refer to the genotypes of the hemagglutinin and neuraminidase, respectively. Suppose that virus 1 is found to be H1N1 and virus 2 is found to be H2N3. What would be the designation for virus 3?
  • b) The antiviral drug amantidine is used to stop or slow down an influenza virus infection. Virus 1 is sensitive to amantidine, while virus 2 is resistant to this antiviral agent. Your mentor predicts that you will find virus 3 to be sensitive to amantidine. What evidence in this electropherogram leads your mentor to suggest this?
  • c) By what genetic mechanism (typical for the Orthomyxoviridae) did virus 3 arise?
  • a) List two molecular events during the influenza virus life cycle that require something provided by the host cell nucleus.
  • b) For which of these events is the physical presence of the nucleus in the cell absolutely required? Why?

9 The data shown in the figure below were obtained for three different isolates of influenza type A virus. The three viruses (designated 1, 2, and 3) were grown in cell culture in the presence of radioactive RNA precursors. The radiolabeled RNA genome segments were then separated by electrophoresis through a polyacrylamide gel. The drawing below shows the relative migration in this gel of each of the genome segments. In addition, the segment number and the viral gene product or products produced by that segment are shown.

10 Reovirus is the prototype member of the family Reoviridae. Describe the features of this virus that make it different from other RNA genome viruses.

11 Hepatitis delta virus (HDV) is classed as a subviral entity. What is a unique feature of the genome replication of this agent?

12 Viroids are infectious agents of plants and are circular, single-stranded RNA molecules. Describe the features of infection of a plant with this kind of agent.

13 In what sense can a prion be described as a "self-replicating entity?"

RNA Gene segment product

PB1 PA PB2

HA NP

8 NS1, NS2

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