Viruses Chapter 19 Christopher Gregg Louisiana State University Questions prepared by Christopher Gregg Louisiana State University Louise Paquin McDaniel College

Which of the following is characteristic of the lytic cycle? Viral DNA is incorporated into the host genome. The virus-host relationship usually lasts for generations. A large number of phages is released at a time. Many bacterial cells containing viral DNA are produced. The viral genome replicates without destroying the host. Answer: c

What is the function of reverse transcriptase in retroviruses? It converts host cell RNA into viral DNA. It hydrolyzes the host cell's DNA. It uses viral RNA as a template for making complementary RNA strands. It translates viral RNA into proteins. It uses viral RNA as a template for DNA synthesis. Answer: e

What characteristics of electron microscopes make them most useful for studying viruses? high energy electrons with high penetrance requirement that specimens be viewed in a vacuum necessity for specimens to be dry and fixed shorter wavelengths providing higher resolution use of magnetic fields to focus electrons Answer d

Why are viruses referred to as obligate parasites? They cannot reproduce outside of a host cell. Viral DNA always inserts itself into host DNA. They invariably kill any cell they infect. They can incorporate nucleic acids from other viruses. They must use enzymes encoded by the virus itself. Answer a

Which of the following is a property of life shared by prokaryotic cells, eukaryotic cells, but not viruses? nucleic acids used to store hereditary information order and complexity in arrangement of biological molecules the ability to process energy through metabolic reactions the capacity to evolve Answer: c This question covers information in Concept 19.2 and can be used to start the lecture.

Which of the following molecules make up the viral envelope? glycoproteins proteosugars carbopeptides peptidocarbs carboproteins Answer: a

You have isolated viral particles from a patient, but you are not sure whether they are rhinoviruses or influenza viruses. The presence of which class of biological molecules would allow you to distinguish between the two types of virus? RNA phospholipids proteins glycoproteins DNA Answer: b Students will need to recognize that influenza viruses have an envelope, but rhinoviruses do not. Refer to Figure 19.3 and Table 19.1.

People with nonfunctional chemokine membrane receptors on their helper T cells as a result of a genetic mutation are immune to HIV infection. Why? HIV cannot enter the host cell. Reverse transcriptase cannot transcribe RNA to DNA. Viral mRNA cannot be transcribed from the integrated provirus. Viruses cannot bud from the host cell. Answer: a This question examines the concept that viruses are able to recognize and attach to host cells via receptor proteins and recognition molecules on the plasma membrane.

Bacteriophages were grown in a medium containing radioactive sulfur (35S) and radioactive phosphorous (32P), which are incorporated into proteins and DNA, respectively. If these phages were used to infect a bacterial culture, which isotope would be detected within the infected bacteria? 35S 32P both neither Answer: b This question relates to the Hershey and Chase experiment. Students should be able to apply the results to viral reproduction.

AZT is a nucleoside analog used to treat HIV infections AZT is a nucleoside analog used to treat HIV infections. It is a thymine (T) nucleoside with an azide group instead of the hydroxyl group found in typical thymine nucleosides. Which step does AZT hamper in the reproductive cycle of the HIV virus? entry into the cell reverse transcription of DNA from RNA transcription of RNA from proviral DNA viral assembly within the cell Answer: b Because AZT is a thymine nucleoside, it will specifically block reverse transcription from RNA to DNA.

You have isolated a sample from an animal suffering from an unknown disease. Which of the following tests would allow you to determine that the animal has a prion disease? Pass the sample through a filter to remove bacteria and see if the filtrate is still infectious. Treat the sample with nuclease and see if it is still infectious. Treat the sample with protease and see if it is still infectious. Heat the sample to normal cooking temperatures and see if it is still infectious. Answer: c You may need to explain what proteases and nucleases are before the students answer the question.

Which of the following most likely describes the vertical transmission of a plant virus? The plant shows symptoms of disease after being grazed on by herbivores. Sap from one plant is rubbed on the leaves of a second plant; both plants eventually show disease symptoms. Seeds are planted and reared under protected conditions, but mature plants show disease symptoms. After a gardener prunes several plants with the same shears, they all show disease symptoms. Answer: c Students will need to distinguish between horizontal transmission of disease and vertical transmission.