Viruses

Figure 21.5 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.

 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? 

Figure 21.10 Which of the following statements is false? 

a. In the lytic cycle, new phages 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. 

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. 

The viral ________ play(s) a role in attaching a virion to the host cell. 

a. core

b. capsid

c. envelope

d. both b and c

Viruses_______. 

a. all have a round shape

b. cannot have a long shape

c. do not maintain any shape

d. vary in shape 

The observation that the bacteria genus Chlamydia contains species that can only survive as intracellular parasites supports which viral origin hypothesis? 

a. Progressive 

b. Regressive 

c. Self-replicating 

d. Virus-first 

A scientist discovers a new virus with a linear, RNA genome surrounded by a helical capsid. The virus is most likely a member of which family based on structure classification? 

a. Rabies virus 

b. Herpesviruses 

c. Retroviruses 

d. Influenza viruses 

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. 

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. 

c. 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. 

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. 

Oncogenic virus cores can be_______. 

a. RNA 

b. DNA 

c. neither RNA nor DNA 

d. either RNA or DNA 

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 bacteriophage can infect ________. 

a. the lungs 

b. viruses 

c. prions 

d. bacteria 

People with the $CCR5\Delta 32$ mutation of a $T$-cell surface protein can be exposed to some strains of$HIV-1$ without becoming sick. What step of the virus life cycle is likely to be inhibited with this mutation? 

a. Release 

b. Reverse transcription 

c. Uncoating 

d. Attachment 

An apple grower notices that several of his apple trees with fungi growing on their trunks have developed necrotic ring spots, while other trees in the orchard that lack fungi appear healthy. What is the most likely conclusion the farmer can make about the virus infecting his apple trees? 

a. The apple trees were infected by horizontal transmission. 

b. The fungi carry disease. 

c. The fungi attract disease-carrying insects. 

d. The apple trees were infected by vertical transmission.

Which of the following is Not used to treat active viral disease? 

a. Vaccines 

b. Antiviral drugs 

c. Antibiotics 

d. Phage therapy 

Vaccines_______. 

a. are similar to viroid's 

b. are only needed once 

c. kill viruses 

d. stimulate an immune response 

A patient presents at the clinic with an acute viral infection. Assays that analyze the viral life cycle classify the virus into Group V with a segmented genome. Which virus is the most likely diagnosis for the patient? 

a. Rabies virus 

b. Picornavirus 

c. HIV-1 

d. Influenza A virus 

Which of the following is not associated with prions? 

a. Replicating shapes 

b. Mad cow disease 

c. DNA 

d. Toxic proteins 

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. 

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? (Hint: Early scientists called viruses “filterable agents.”) 

Varicella-zoster virus is a double-stranded DNA virus that causes chickenpox. How does its genome structure provide an evolutionary advantage over a single stranded DNA virus? 

Classify the Rabies virus (a rhabdovirus family member) and HIV-1 with both the Baltimore and genomic structure systems. Compare your results. What conclusions can be made about these two different methods? 

Why can’t dogs catch the measles? 

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

In this section, you were introduced to different types of viruses and viral diseases. Briefly discuss the most interesting or surprising thing you learned about viruses. 

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

A bacteriophage with a lytic life cycle develops a mutation that allows it to now also go through the lysogenic cycle. How would this provide an evolutionary advantage over the other bacteriophages that can only spread through lytic cycles? 

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? 

The vaccine Gardasil that targets human papilloma virus (HPV), the etiological agent of genital warts, was developed after the anti-HPV medication podofilox. Why would doctors still want a vaccine created after anti-viral medications were available? 

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 contract this disease? 

How are viroids like viruses? 

A botanist notices that a tomato plant looks diseased. How could the botanist confirm that the agent causing disease is a viroid, and not a virus?