Campbell Biology in Focus, Chapter 17 Viruses

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 6,300 nucleotides. Its capsid is 25-30 nm in diameter and contains 180 identical capsomeres. If the yellow mottle virus capsid has 20 facets, how many proteins form each facet?

9

Which of the following series best reflects what we know about how the flu virus moves between species?

An animal such as a pig is infection with more than one virus, genetic recombination occurs, the new virus mutates and is passed to a new species such as a bird, and the virus mutates and can be transmitted to humans.

What is the function of reverse transcriptase in retroviruses?

It uses viral RNA as a template for DNA synthesis

*Refer to 17.2 of The Viral Reproductive Cycle* When new viruses are being assembled (IV), what mediates the assembly?

Nothing; they self-assemble

Which of the following statements describes the lysogenic cycle of the lambda phage?

The phage genome replicates along with the host genome

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. Which of the following would be expected to occur?

The plants would develop the typical symptoms of TMV infection.

Which of the following describes plant virus infections?

They are spread via the plasmodesmata.

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 the bacteriophage?

control of more than one gene in an operon

Which of the following accounts for someone who has had a herpesvirus-mediated cold sore or genital sore getting flare-ups for the rest of his or her life?

copies of the herpesvirus genome permanently maintained in host nuclei

*Refer to Figure 17.1* Which of the three types of viruses shown would you expect to include a capsid?

all three

Viral envelopes can best be analyzed with which of the following techniques?

antibodies against specific proteins not found in the host membranes

RNA viruses require their own supply of certain enzymes because

host cells lack enzymes that can replicate the viral genome.

Which of the following characteristics, structures, or processes is common to both bacteria and viruses?

genetic material composed of nucleic acid

Which of the following can be effective in preventing the onset of viral infection in humans?

getting vaccinated

Antiviral drugs that have been useful are usually associated with which of the following properties?

interference with viral replication

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

Which of the following is characteristic of the lytic cycle?

A large number of phages are released at a time.

Table 17.1 shows the results of testing five viruses (A-E) for nuclease specificity, the ability of the viral genome to act as an mRNA, and the presence (+) or absence (-) of each virus's own polymerase. Based on the table, which virus meets the Baltimore requirements for a bacteriophage?

A- Dnase sensitivity, unable to act as an mRNA, and absence of virus's own polymerase

In order to be able to remain latent in an infected live cell, HSV must be able to shut down what process?

Apoptosis of a virally infected cell.

Why do RNA viruses appear to have higher rates of mutation?

Replication of their genomes does not involve proofreading.

Table 17.1 shows the results of testing five viruses (A-E) for nuclease specificity, the ability of the viral genome to act as an mRNA, and the presence (+) or absence (-) of each virus's own polymerase. Based on the table, which virus meets the Baltimore requirements for a retrovirus?

D- Rnase sensitivity, ability to act as an mRNA, and presence of virus's own polymerase

*Refer to Figure 17.1* Which of the three types of viruses shown would you expect to include glycoproteins?

I and II ony

You isolate an infectious substance that is capable of causing disease in plants, but you do not know whether the infectious agent is a bacterium, virus, viroid, or prion. You have four methods at your disposal that you can use to analyze the substance in order to determine that nature of the infectious agent. I. treating the substance with nucleases that destroy all nucleic acids and then determining whether it is still infectious II. filtering the substance to remove all elements small than what can be easily seen under a light microscope III. culturing the substance by itself on nutritive medium, away from any plant cells IV. treating the sample with proteases that digest all proteins and then determining whether it is still infectious If you already knew that the infectious agent was either bacterial or viral, which treatment would allow you to distinguish between these two possibilities?

III. culturing the substance by itself on nutritive medium, away from any plant cells

Emerging viruses arise by

Mutation of existing viruses, the spread of existing viruses to new host species, the spread of existing viruses more widely within their host species (All of the above)

A bacterium is infected with an experimentally constructed bacteriophage composed of the T2 phage protein coat and the T4 phage DNA. The new phages produced will have

T4 protein and T4 DNA

Which of the following is the most probable fate of a newly emerging virus that causes high mortality in its host?

The newly emerging virus will die out rather quickly or will mutate to be far less lethal

In electron micrographs of HSV infection, it can be seen that they intact virus initially reacts with cell-surface proteoglycans, then with specific receptors. This is later following 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 enters into the nuclear membrane, and the genome is all that enters the nucleus.

Most molecular biologists think that viruses originated from fragments of cellular nucleic acid. Which of the following observations support this theory?

Viral genomes are usually similar to the genome of the host cell.

Which of the following is the best predictor of how much damage a virus causes?

ability of the infected cell to undergo normal cell division

A human pandemic is

an epidemic that extends around the world

You isolate an infectious substance that is capable of causing disease in plants, but you do not know whether the infectious agent is a bacterium, virus, viroid, or prion. You have four methods at your disposal that you can use to analyze the substance in order to determine that nature of the infectious agent. I. treating the substance with nucleases that destroy all nucleic acids and then determining whether it is still infectious II. filtering the substance to remove all elements small than what can be easily seen under a light microscope III. culturing the substance by itself on nutritive medium, away from any plant cells IV. treating the sample with proteases that digest all proteins and then determining whether it is still infectious If you already knew that the infectious agent was either a viroid or a prion, which treatment would allow you to distinguish between these two possibilities?

either I or IV. I. treating the substance with nucleases that destroy all nucleic acids and then determining whether it is still infectious IV. treating the sample with proteases that digest all proteins and then determining whether it is still infectious

*Refer to 17.2 of The Viral Reproductive Cycle* At the arrow marked II, what enzyme(s) are being utilized?

host cell DNA polymerase

If scientists are trying to use what they know about HSV to devise a means of protecting other people from being infection, which of the following would have the best chance of lowering the number of new cases of infection?

interference with new viral replication in preexisting cases

Which viruses have single-stranded RNA that acts as a template for DNA synthesis?

retroviruses

The host range of a virus is determined by

the proteins on its surface and that of the host