Chapter 8 Study Questions

What are the minimal components needed for a virion?

capsid and genome

Mutations contribute to the vast diversity of viruses. What viral genetic type has the most stable genome and the lowest mutation rate?

double-stranded DNA virus

Viruses go through phases during which they are actively replicating and destructive to the host cell, or dormant within the host cell. During which part of the bacteriophage life cycle will the viral genome be replicated in synchrony with the host cell?

lysogenic phase

Viral structural proteins and proteins involved in the release of new viral particles that are synthesized after genomic replication begins would be considered

middle and late proteins

A retrovirus has a genome that consists of __________.

ssRNA

What is the benefit, for a virus, to be a temperate or lysogenic virus?

A single infection event can produce millions of new viral particles instead of hundreds of viral particles.

If viruses were able to infect the vast majority of host cells, evolution would have stalled. According to the chapter, what is one way that cells have evolved to avoid viral infection?

An attachment receptor on the host cell surface that is recognized by the virus is mutated, making the host resistant to infection.

In which stage does formation of mature viruses occur?

Assembly

When determining the number of bacterial virus particles in a suspension, why is the number obtained always less than the actual viral titer?

Because all of the virus particles do not infect with 100% efficiency.

The host DNA is usually degraded during which stage?

Biosynthesis

Some viruses, especially animal viruses, have an envelope surrounding their nucleocapsid. This envelope may have viral proteins embedded in it. Why are the viral proteins more readily recognized and targeted by the immune system than the envelope?

Enveloped viruses are often coated with animal cell membrane as they leave the cell. This membrane is a major component of the viral envelope. The viral proteins are more readily recognized by the immune system, as they are more distinct from the materials normally found in and on the cells. However, the envelope can contain several types of viral components as well.

Differentiate between persistent and latent animal virus infections.

In a persistent infection, the host cell is continually releasing new viral particles slowly. In a latent infection, there are periods of time where the virus is not replicating and creating new viral particles.

In which stage is the viral DNA introduced into the cell?

Penetration

Which of the following types of enzymes would a virus need to provide in order to replicate within a cell? In other words, which of these enzymes would not normally be found in a cell unless a virus provided it?

RNA replicases (RNA-dependent RNA polymerases) for RNA viruses

Which of the following groups contains some representatives with genomes that are so small that they may have as few as two genes?

RNA viruses

Retroviruses mutate relatively rapidly. What is one of the reasons?

Reverse transcriptase lacks the proofreading function found in many DNA polymerases, so mutations accumulate more easily.

How is penetration different in animal viruses as compared to bacterial viruses?

The entire viral particle penetrates an animal cell, while only the viral genome penetrates a bacterial cell.

Plaque assays are often used to estimate the number of virions in a sample of a particular volume (the titer). The count is given as plaque-forming units. Which of the following is NOT generally a concern that must be considered in evaluating the results of plaque assays?

The largest problem is that single viruses may create multiple plaques, resulting in overestimates of the number of viruses present.

What would be the fate of a lytic bacteriophage if the host cell died prior to the assembly stage?

The virus would not be able to infect new hosts.

How are viruses different from cells?

They require a host in order to reproduce.

What is the function of the structural elements of a virus?

To package and protect the viral genome

Which of the following accurately describe viruses?

Viruses are as old as Bacteria and Archaea. Viruses are unable to perform replication on their own. Viruses are smaller than Bacteria and Archaea. The genetic information of a virus can be in the form of RNA or DNA. Viruses cannot replicate on their own. Viruses do not belong to any of the three domains: Bacteria, Archaea, and Eukarya.

Which of the following is true about viral infection?

Viruses are very specific in which cells they infect. For a virus to be taken up by a cell, it must find a cell with appropriate receptors on the surface. It cannot be taken up by cells without the appropriate receptors.

Based on what is currently thought about lytic versus lysogenic life cycles, which of the following viruses would be most likely to be found as a prophage?

a virus that is found in a low-density population of host bacteria deep in the ocean