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Answers to Text Questions
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Inquiry Questions

None for this chapter.

Self Test

1). Viruses consist of a ________________ core surrounded by a protein coat.
    a). RNA
    b). DNA
    c). chromosome
    d). nucleic acid
Answer: d

2). Phages infect bacterial cells by
    a). poking holes in the cell and injecting their DNA.
    b). destroying the bacterial cell wall.
    c). receptor-mediated endocytosis.
    d). exocytosis.
Answer: a

3). The end result of the viral lytic cycle is
    a). the release of new viruses.
    b). the incorporation of viral genome into the host genome.
    c). the conversion of the virus into a prophage.
    d). Both b and c are correct.
Answer: a

4). The alteration of a cell's genome by the incorporation of foreign DNA is called
    a). genetic conversion.
    b). mutation.
    c). transformation.
    d). reverse transcription.
Answer: c

5). Which of the following is a viral glycoprotein that plays a role in the infection of human cells by HIV?
    a). gp120
    b). CD4
    c). CCR5
    d). Both b and c are correct.
Answer: a

6). The HIV enzyme, ________________, produces a DNA copy of the viral genome once it is inside the host cell.
    a). DNA polymerase
    b). reverse transcriptase
    c). RNA polymerase
    d). helicase
Answer: b

7). The drug AZT and its analogs functions by
    a). inhibiting the replication of viral nucleic acid.
    b). blocking the production of envelope proteins.
    c). blocking the production of capsid proteins.
    d). blocking the binding of the virus to human cell receptors.
Answer: a

8). What is the function of the CD8+ cell antiviral factor (CAF) in human white blood cells?
    a). disables the CD4 receptor
    b). blocks replication of the HIV virus
    c). interferes with the production of viral proteins
    d). blocks the CCR5 or CXCR4 receptors
Answer: b

9). New strains of flu viruses are most likely to arise in the Far East because
    a). of overpopulation in these areas.
    b). adequate sanitation is lacking.
    c). common hosts (ducks, chickens, pigs) live in close proximity to humans.
    d). of environmental mutagens that cause changes in viral RNA.
Answer: c

10). Which of the following infectious agents does not contain protein?
    a). viruses
    b). viroids
    c). prions
    d). none of these
Answer: b

Test Your Visual Understanding

1). Describe the overall shape of each of the viruses in the figure, either as helical, isometric, or icosahedral.
Answer: (a) This bacteriophage has a spherical head so it is isometric but the head is made up of triangular facets and so the head is also icosahedral in shape. The tail region is helical. (b) This tobacco mosaic virus is helical in shape. (c) This HIV virus is isometric and although not visible, it is most likely composed of triangular facets (as most viruses are) and is therefore also icosahedral.

2). List which of these viruses attacks:
    a). animals
    b). plants
    c). bacteria
    a). animals?(c) Human immunodeficiency virus (HIV)
    b). plants? (b) Tobacco mosaic virus (TMV)
    c). bacteria? (a) Bacteriophage

Apply Your Knowledge

1). AIDS was first identified in 1981 in the United States, and in 2002, an estimated 495,000 cases of AIDS and/or HIV had been reported. The total U.S. population at the end of 2002 was approximately 290 million. What percent of the population was living with AIDS and/or HIV?
Answer: To find the percent of individuals with AIDS in the total population, divide the number of individuals with AIDS and/or HIV by the total population and multiply by 100 or:
(495,000 / 290,000,000) x 100 = 0.17%

2). In what ways might the early, self-replicating particles that gave rise to the first organisms have resembled, or differed from, viruses?
Answer: In order to be self-replicating, these early precursors to organisms had to contain a molecule that could be replicated, most likely RNA- or DNA-like viruses. Unlike viruses, these early precursors to organisms most likely encased their nucleic acid in a lipid membrane rather than a protein coat as viruses do. The temperatures of early earth were very hot and would most likely have denatured proteins. In the hot, aquatic environment a lipid membrane would offer more protection for the nucleic acid than protein.

3). If a viral disease such as influenza could kill 22 million people over 18 months in 1918–1919, why do you suppose the killing ever stopped? What prevented the flu virus from continuing its lethal assault on humanity?
Answer: Just as mutation and recombination gives rise to new, more lethal strains of flu viruses, they can also make the virus more easily attacked by the human immune system. Point mutations of the surface proteins occur in 1 in every 100,000 viruses and although a strain of viruses may be particularly lethal, the viruses of that strain continue to mutate and undergo recombinations. Eventually, the virus may change in a way that the human immune system can now kill it, making the virus less lethal. After 18 months, the viruses most likely mutated and underwent recombination to the point where they were less lethal and the infected individuals could fight off the disease.

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