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Exam 33: Viruses

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Question 1

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Why do scientists consider HIV to be an emerging virus?

A) HIV mutates so rapidly that the virus of today has very little similarity to the virus in the first AIDS patients from the early 1980s.
B) HIV used to infect only chimps, but it has mutated in such a way that it now infects humans.
C) HIV is now starting to cause diseases other than AIDS, such as rare types of cancers and pneumonias.
D) HIV infected humans long before AIDS first become a problem in the early 1980s, but it has now mutated to a more deadly form.

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Question 2

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Figure 33.1 -Which of the following statements applies to lysogeny?

A) Viral proteins are used to replicate the viral genome.
B) The viral genome integrates into the host cell's genome.
C) When the cell divides, the daughter cells are no longer infected.
D) Viral particles are produced continuously.

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Question 3

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When people die from HIV infections, it is usually because they

Which of the following is a reason why viruses are considered non- living?

You have isolated a newly discovered virus and are attempting to characterize it. You begin with its genome. You first isolate the virion- producing mRNA from culture cells infected with the virus. When you compare these mRNA with the viral genome, you find that they are complementary. What does this tell you?

Viruses use the host's machinery to make copies of themselves. However, some human viruses require a type of replication that humans do not normally do. For example, humans normally do not have the ability to convert RNA into DNA. How can these types of viruses infect humans, when human cells cannot perform a particular role that the virus requires?

Which of the following is true regarding the ambi- sense virus?

Use the following information when answering the corresponding questions) . It has been shown that there are two distinct variants of the HIV virus Bleul et al. 1997. The HIV coreceptors CXCR4 and CCR differentially regulated on human T- lymphocytes. Proceedings of the National Academy of Science 94:1925- 30) . One virus preferentially infects macrophages and is called M- tropic. The other preferentially infects T cells and is called T- tropic. The M- tropic viruses use CCR5 and CD4 as coreceptors, and the T- tropic viruses use CXCR4 and CD4 as coreceptors. The M- tropic viruses are found early in HIV infections; the T- tropic viruses are found late in infections, when AIDS symptoms are prevalent. T- tropic viruses are associated with a drastic decrease in T cells. Macrophages go to the site of wounds, where they are used to fight infections. T cells circulate in the body and fight infections at many sites. -Which receptors for HIV would you expect to find on macrophages and T cells?

Use the following information when answering the corresponding questions) . It has been shown that there are two distinct variants of the HIV virus Bleul et al. 1997. The HIV coreceptors CXCR4 and CCR differentially regulated on human T- lymphocytes. Proceedings of the National Academy of Science 94:1925- 30) . One virus preferentially infects macrophages and is called M- tropic. The other preferentially infects T cells and is called T- tropic. The M- tropic viruses use CCR5 and CD4 as coreceptors, and the T- tropic viruses use CXCR4 and CD4 as coreceptors. The M- tropic viruses are found early in HIV infections; the T- tropic viruses are found late in infections, when AIDS symptoms are prevalent. T- tropic viruses are associated with a drastic decrease in T cells. Macrophages go to the site of wounds, where they are used to fight infections. T cells circulate in the body and fight infections at many sites. -Poliovirus is an RNA virus of the picornavirus group, which uses its RNA as mRNA. At its 5' end, the RNA genome has a viral protein VPg) instead of a 5' cap. This is followed by a nontranslated leader sequence, and then a single long protein- coding region ~7000 nucleotides) , followed by a poly- A tail. Observations were made that used radioactive amino acid analogues. Short- period use of the radioactive amino acids results in labelling of only very long proteins, while longer periods of labelling result in several different short polypeptides. What conclusion is most consistent with the results of the radioactive labelling experiment?

As obligate intracellular parasites, viruses have which of these characteristics?

The HIV protease has been the target of several anti- HIV medications. This antiviral strategy is possible because

What is difference between an epidemic and a pandemic?

If a viral host cell has a mutation that interferes with the addition of carbohydrates to proteins in the Golgi, which of the following could likely result?

Which of the following viruses would have a disrupted replication cycle if their reverse- transcriptase enzyme was non- functional?

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. We expect that the plants would

Which of the following viruses would be the most likely to have reverse transcriptase?

When HIV infects people, it does not immediately induce AIDS and kill its host. When people die from HIV infections, it is usually because

HIV is inactivated in the laboratory after a few minutes of sitting at room temperature; the flu virus is still active after sitting for several hours. What are the practical consequences of these findings?

Figure 33.1 -Using the data in Figure 33.1, how long does it take for virus B to go through one lytic cycle?

You are a physician, and you suspect your patient has a viral infection that has never been seen in humans. The infection is localized in the cells along the lining of the small intestine. The cells in this area are regularly sloughed off and replaced with new cells; that is, these cells are constantly dividing. When you isolate this new virus and incubate it in culture, you discover that it does not replicate well in cultures that have slowly dividing cells, but it does much more damage in cultures that have actively dividing cells. What do these findings suggest about this new virus?