Chp 8

Which of the following examples is an example of lysogenic conversion?

Vibrio cholerae bacteria produce cholera toxin when infected with a phage.

The host DNA is usually degraded during which stage?

Biosynthesis

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.

A retrovirus has a genome that consists of __________.

ssRNA

single-stranded RNA and double-stranded RNA

viruses carry their own nucleic acid polymerases (called replicases) to replicate the viral genome with no DNA intermediate.

retro-

viruses contain an RNA-dependent DNA polymerase called reverse transcriptase that is used generate a DNA intermediate.

single-stranded RNA

viruses have genome configurations that are either plus-sense or minus-sense.

double-stranded DNA

viruses have processes of replication, transcription, and translation that are the most similar to those used by cells.

single-stranded DNA

viruses have replication that involves first generating a complementary DNA strand.

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

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

Non-virophage viruses only

The genetic information of can be in the form of DNA or RNA.

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.

Lysogenic viral DNA integrating into the host genome is referred to as

a prophage.

Which of the following are viable methods of release of newly assembled viral particles?

budding or lysis of host cell

Considering T4 bacteriophage infection of a bacterial cell, which would be an example of the earliest phage proteins transcribed and translated?

enzymes for the synthesis and glucosylation of the unusual T4 base 5-hydroxymethylcytosine

double-stranded DNA

is the genetic material of virophages.

Place the steps in the bacteriophage replication cycle into the correct order.

1. Attachment ( adsorption of phage virion) 2. Penetration of viral nucleic acid 3. Synthesis of viral nucleic acid and proteins 4. Assembly and packaging of new viruses 5. Cell lysis and release of new Virions

What is the benefit for a bacteriophage to be a temperate (or lysogenic) virus?

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

What structure can the viral genome take?

All of the listed responses are correct.

The introductory passage discusses the way that virophages interfere with the ability of megaviruses to reproduce and the possible selective benefits of this. However, there are many ways that cells attempt to survive attacks by viruses. According to the chapter, what is another 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.

In which stage does formation of mature viruses occur?

Assembly

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.

Which of the following events might trigger induction of a temperate bacteriophage?

Exposure to UV light

What is the fate of the prophage during the lysogenic stage?

It is copied every time the host DNA replicates.

Based on your understanding of the chapter material and the information in the passage, which of the following best defines something as a virus? Are virophages a type of virus or something different?

It must have a capsid and a nucleic acid, which can be double-stranded or single-stranded, circular or linear, and DNA or RNA. Virophages are therefore a type of virus.

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

Penetration

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

How is the lytic cycle different from the lysogenic cycle with respect to the infected host cell?

The host cell dies during the lytic stage.

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.

Virophages only

They are always smaller than Bacteria and Archaea. They lack the genes for proteins needed to replicate themselves.

Both virophages and other viruses

They cannot replicate on their own. They do not belong to any of the three domains (Bacteria, Archaea and Eukarya). They have a protein capsid surrounding their nucleic acid.

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.

Some viruses have plus sense RNA genomes. Which of the following could describe one of those viruses?

a virus that contains RNA with the same nucleotide sequence as the functional mRNA that its host cell will translate to produce viral products

What component(s) make up the structure of a virion?

capsid and genome

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

Place the steps in retrovirus replication into the correct order on the diagram.

1. Entry and uncoating of the retrovirus 2. Reverse transcriptase activity (Two steps) 3. Viral DNA enters nucleus and intergrates into the host cell genome 4. Transcription by host RNA polymerase forms viral mRNA and genome copies 5. Translation of mRNA form viral proteins; new nucleocapsids assembled and released by budding

Virophages interfere with the life cycle of megaviruses by competing with them for replication enzymes, causing defective megaviruses to be produced. When the life cycle occurs correctly, what are the steps?

1. The virus attaches to the host cell, which can be mediated by cell surface receptors. 2. Penetration of nucleic acids into the host cell and the capsid is discarded. 3. Host cell enzymes and replicationmachinery are used to synthesize new viral genetic and capsid material. 4. Newly synthesized viral genomes and capsids are assembled into complete viral particles. 5. The host cell lyses, releasing the newly assembled virus particles.

Retroviruses become proviruses integrated into the host chromosome soon after infecting the host cell, and can remain there indefinitely. The provirus DNA can then be transcribed and translated by the host cell, making new retroviral RNA genomes, enzymes, and structural proteins. New retroviral virions can then assemble and bud through the host cell membrane continuously over long periods of time. What is one implication of this retroviral life cycle?

It is difficult to completely cure an animal host of the virus, since anti-retroviral drugs will only eliminate circulating virions, not proviruses.

Why does the structure of plant and bacterial cells illustrate the reason for having few enveloped viruses that infect these cells?

Plant and bacterial cells contain cell walls that limit the virus from budding out and obtaining the envelope.

Viruses rely on the host cell machinery to make new viruses, but they sometimes provide their own enzymes (such as reverse transcriptase, which is an RNA-dependent DNA polymerase). 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

Neither virophages nor other viruses

They generate energy through mitochondria. They use their own ribosomes to make proteins.

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

When determining the number of 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

Megaviruses have a particular life cycle in which new viral particles are produced, and then the host cell lyses, although virophages can compete with them for replication enzymes. Viruses have many types of life cycles and can go through phases during which they are actively replicating and destructive to the host cell or dormant within the host cell. These life cycles differ in different types of viruses, so the cycle of megaviruses differs from those of bacteria and animals. During which part of the bacteriophage life cycle will the viral genome be replicated in synchrony with the host cell?

lysogenic

single-stranded DNA and double-stranded DNA

viruses replicate using DNA polymerases, either their own or from those of the host.