Chapter 21 Questions

Prions are responsible for variant Creutzfeldt-Jakob Disease, which has resulted in over 100 human deaths in Great Britain during the last 10 years. How do humans obtain this disease?

This prion based disease is transmitted through human consumption of infected meat

Influenza virus is packaged in a viral envelope that fuses with the plasma membrane. This way, the virus can exit the host cell without killing it. What advantage does the virus gain by keeping the host cell alive?

The host cell can continue to make new virus particles.

Which statement is true of viral replication? a. In the process of apoptosis, the cell survives. b. During attachment, the virus attaches at specific sites on the cell surface. b. The viral capsid helps the host cell produce more copies of the viral genome. d. mRNA works outside of the host cell to produce enzymes and proteins.

B

Which statement is true? a. A virion contains DNA and RNA. b. Viruses are acellular. c. Viruses replicate outside of the cell. d. Most viruses are easily visualized with a light microscope.

B

Which of the following statements is false? a. In the lytic cycle, new phage are produced and released into the environment. b. In the lysogenic cycle, phage DNA is incorporated into the host genome. c. An environmental stressor can cause the phage to initiate the lysogenic cycle. d. Cell lysis only occurs in the lytic cycle. vary in shape

c

Which is true of DNA viruses? a. They use the host cell's machinery to produce new copies of their genome. b. They all have envelopes. c. They are the only kind of viruses that can cause cancer. d. They are not important plant pathogens.

A

Which statement is true of viroids? a. They are single-stranded RNA particles. b. They reproduce only outside of the cell. c. They produce proteins. d. They affect both plants and animals.

A

Which of the following is NOT used to treat active viral disease? a. vaccines b. antiviral drugs c. antibiotics d. phage therapy

C

Which of the following is not associated with prions? a. replicating shapes b. mad cow disease c. DNA d. toxic proteins

C

Which statement is true of reverse transcriptase? a. It is a nucleic acid. b. It infects cells. C. It transcribes RNA to make DNA. D. It is a lipid.

C

A bacteriophage can infect ________. a. the lungs b. viruses c. prions d. bacteria

D

Oncogenic virus cores can be_______. a. RNA b. DNA c. neither RNA nor DNA d. either RNA or DNA

D

The viral ________ plays a role in attaching a virion to the host cell. a. core b. capsid c. envelope d. both b and c

D

Vaccines_______. a. are similar to viroids b. are only needed once c. kill viruses d. stimulate an immune response

D

Viruses_______. a. all have a round shape b. cannot have a long shape c. do not maintain any shape c. vary in shape

D

Which of the following statements about virus structure is true? a. All viruses are encased in a viral membrane. b. The capsomere is made up of small protein subunits called capsids. c. DNA is the genetic material in all viruses. d. Glycoproteins help the virus attach to the host cell.

D

Which statement is not true of viral replication? a. A lysogenic cycle kills the host cell. b. There are six basic steps in the viral replication cycle. c. Viral replication does not affect host cell function. d. Newly released virions can infect adjacent cells.

D

Although plant viruses cannot infect humans, what are some of the ways in which they affect humans?

Plant viruses infect crops, causing crop damage and failure, and considerable economic losses.

Why is immunization after being bitten by a rabid animal so effective and why aren't people vaccinated for rabies like dogs and cats are?

Rabies vaccine works after a bite because it takes weeks for the virus to travel from the site of the bite to the central nervous system, where the mosts ever symptoms of the disease occur. Adults are not routinely vaccinated for rabies for two reasons: first, becauset he routine vaccination of domestic animals makes it unlikely that humans will contract rabies from an animal bite; second, if one is bitten by a wild animal or a domestic animal that one cannot confirm has been immunized, there is still time to give the vaccine and avoid the often fatal consequences of the disease.

One of the first and most important targets for drugs to fight infection with HIV (a retrovirus) is the reverse transcriptase enzyme. Why?

Reverse transcriptase is needed to make more HIV-1 viruses, so targeting the reverse transcript ase enzyme maybe away to inhibit the replication of the virus. Importantly, by targeting reverse transcriptase, we do little harm to the host cell, since host cells do not make reverse transcriptase. Thus, we can specifically attack the virus and not the host cell when we use reverse transcriptase inhibitors.

Why can't dogs catch the measles?

The virus can't attach to dog cells, because dog cells do not express the receptors for the virus and/or there is no cell within the dog that is permissive for viral replication.

How are viroids like viruses?

They both replicate in a cell, and they both contain nucleic acid.

The first electron micrograph of a virus (tobacco mosaic virus) was produced in 1939. Before that time, how did scientists know that viruses existed if they could not see them?

Viruses pass through filters that eliminated all bacteria that were visible in the light microscopes at the time. As the bacteria-free filtrate could still cause infections when given to a healthy organism, this observation demonstrated the existence of very small infectious agents. These agents were later shown to be unrelated to bacteria and were classified as viruses