Biology, Eighth Edition (Raven)

Chapter 27: Viruses

Pre Test

Why do some viruses only interact with certain parts of the body (e.g. rabies targets nerve cells and not those of the mouth and nose?) (p. 524)
A)The immune systems around various tissues have different strengths and weaknesses depending on the types of viruses.
B)The genetic instructions differ between cell types in an individual. The viruses must capitalize on special genes that the host cells contain in order to infect them.
C)Viral infection requires that proteins of the capsid can bind to specific surface proteins on the host cell. Cells of different tissues have different types of surface proteins.
D)If a virus contacts an incompatible cell, it is likely to be engulfed and degraded.
E)Both a and c are correct.
True or false: Infection of a bacterium by a lytic phage leads to integration of the viral genome into the host's chromosome. (p. 528)
Why must the reverse transcriptase gene be encoded in the HIV genome? (p. 531)
A)The virus creates the reverse transcriptase protein while circulating in a victim's blood stream in order to be able to enter his or her cells.
B)Reverse transcriptase is used to convert the HIV genome into double-stranded DNA in order to insert into one of the victim's chromosomes.
C)Assembly of the virus is regulated by reverse transcriptase, and therefore this gene is not likely to be found in a normal, uninfected individual's genome.
D)Reverse transcriptase helps assemble the glycoproteins, such as gp120, which are required for identifying and binding to host cells.
E)Genetic expression of the virus is regulated by reverse transcriptase. Without it, the host cell would not be able to synthesize HIV proteins.
Why are particles classified as emerging viruses usually considered so threatening to public health? (p. 534)
A)They occur randomly, through mutation, and therefore cannot be anticipated by public health systems.
B)Their method of infection is airborne: that is, they emerge from the respiratory system of infected people and are therefore rapidly passed along.
C)They appear and disappear quickly in populations so they can't be tracked.
D)Emergent viruses become established in one species and, on rare occasions, mutate to infect another. This means the new species has no innate defense mechanisms so the disease is severe.
E)They emerge from the cell membrane of an infected cell without lysing it. This means that the cell produces virus particles for the duration of its life.
Which of the following would most completely degrade a viroid? (p. 536)
D)Both a and b would be required.
E)All of a, b, and c would be required for complete degradation of a viroid.
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