Chapter 33

Which of the following is characteristic of the lytic cycle?

A large number of phages are released at a time.

Which of the following human diseases is caused by a virus that requires reverse transcriptase to transcribe its genome inside the host cell?

AIDS

What is the difference between an epidemic and a pandemic?

An epidemic is restricted to a local region; a pandemic is global.

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

Identify the receptor this virus uses and develop an enzyme that blocks the receptor.

You believe that you have isolated a new strain of positive-sense, single-stranded RNA virus and set about studying it in your laboratory. Which of the following lines of evidence would most strongly support your hypothesis that the virus is a [+]ssRNA?

Introducing a protease inhibitor causes the virus to stop producing proteins and reproducing.

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?

It is a double-stranded DNA virus.

What is the function of reverse transcriptase in retroviruses?

It uses viral RNA as a template for DNA synthesis.

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 labeling of only very long proteins, while longer periods of labeling result in several different short polypeptides. What conclusion is most consistent with the results of the radioactive labeling experiment?

The RNA is only translated into a single long polypeptide, which is then cleaved into shorter ones.

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 have. 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?

The viral genome has genes coding for enzymes needed for its own reproduction.

Which of the following supports the argument that viruses are nonliving?

They are not cellular.

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 cultured cells infected with the virus. When you compare this mRNA to the viral genome, you find that they are complementary. What does this tell you?

This virus has a negative-sense genome.

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

an RNA-based lysogenic virus

Viral envelopes can best be analyzed with which of the following techniques?

antibodies against specific proteins not found in the host membranes

Mimivirus contains some of the genes required for protein synthesis. This is cited as support for which hypothesis about the origins of viruses?

degeneration

Which of the following characteristics, structures, or processes is common to bacteria and viruses?

genetic material composed of nucleic acids

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

have too few T cells to adequately fight infection

Effective antiviral drugs are usually associated with which of the following properties?

interference with viral replication

A biologist develops a new drug that seems to dramatically slow the onset of symptoms resulting from HIV infection. Close monitoring of HIV-infected cells reveals that the viral proteins are in the form of long polyproteins. The biologist most likely developed a ________.

protease inhibitor

A virus consisting of a single strand of RNA, which is transcribed into complementary DNA, is a ________.

retrovirus

Which viruses have single-stranded RNA that acts as a template for DNA synthesis?

retroviruses

Which of the following could use reverse transcriptase to transcribe its genome?

ssRNA

A population of viruses with similar characteristics is called a ________.

strain

The virus genome and viral proteins are assembled into virions (virus particles) during ________.

the lytic cycle only