Exam 33: Viruses

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. -What would the result be if a drug that blocks the action of RNA polymerase was introduced into a virus- infected organism?

Does treating a viral infection with antibiotics affect the course of the infection?

Figure 33.1 -Cells were infected with approximately 1000 copies of either virus A or virus B at the 0 time point. At 5- minute intervals, a sample of the virus and cell mixture was removed. The intact cells were removed from the sample, and the number of viruses per milliliter of culture was determined. Using the data in Figure 33.1, how long does it take for virus A to go through one lytic cycle?

What is the main structural difference between enveloped and nonenveloped viruses?

You have isolated the genome from a novel virus and would like to determine its composition. You have three tu each containing one of these substances: 1) a protein that degrades dsDNA DNase, tube 1) 2) a protein that degrades ssRNA RNase, tube 2) 3) a protease that degrades viral proteins tube 3) You add some of your novel genome to tubes 1, 2, and 3. The genome is degraded in tube 2, but not in tube 1 or t 3) Based on your knowledge of genome types that have been found in viruses, what could the genome's composition be?

In doing gene therapy, researchers frequently use attenuated viruses. The goal of gene therapy is to insert a normal copy of the mutated, disease- causing gene into the patient's genome, so that they will start producing normal protein. Which type of virus is suited to this application?

It is believed that HIV has passed from chimps to humans more than once. This is very telling since it suggests that animal- to- human viral transmissions may be more common than previously thought. What is the best evidence in support of the conclusion that HIV made the chimp- to- human leap more than once?

The first class of drugs developed to treat AIDS-such as AZT-were known as reverse transcriptase inhibitors. What was the mechanism by which they worked to treat HIV infections?

Which of the following is the most important reason that developing treatments and vaccines, as well as staging an effective immune response for HIV infections, has been so difficult compared with other viruses?

To make a vaccine against mumps, measles, or rabies, which type of viruses would be useful?

You just discovered a new virus. This virus infects heart muscle, where it causes inflammation. This virus has a very high mutation rate. Which of the following is the best strategy for finding a treatment for this virus?

What is a significant difference between lytic and lysogenic viral growth?

Which of the following plays an important role in the ability of an enveloped virus to fuse with the host cell?

You have isolated the genome from a novel virus and would like to determine its composition. You have three tu each containing one of these substances: 1) a protein that degrades dsDNA DNase, tube 1) 2) a protein that degrades ssRNA RNase, tube 2) 3) a protein that degrades other proteins protease, tube 3) You add some of your novel genome to tubes 1, 2, and 3. The genome is not degraded in tube 1, 2, or 3. Based on your knowledge of genome types that have been found in viruses, what could the genome's composition be?

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 6300 nucleotides. Its capsid is 25 -30 nanometres in diameter and contains 180 identical capsomeres. If the yellow mottle virus begins its infection of a cell by using its genome as mRNA, which of the following would you expect to be able to measure?