Julianne Zedalis; John Eggebrecht

28 .

How did the development of a porcelain filter, called the Chamberland-Pasteur filter, help scientists discover viruses?

After filtering a liquid plant extract, the scientists could see the virions using the light microscope.
After filtering a liquid plant extract, the disease was still transferred to a healthy plant.
After filtering a liquid plant extract, the virus cells multiplied.
After filtering a liquid plant extract, scientists were able to trace historical footprints.

29 .

Scientists have proposed a few hypotheses to explain the origin of viruses. Determine which of the following developments best explains how and why scientists clarify and further refine such hypotheses.

Advances in technology provide historic evidence.
Biochemical and genetic information provide historic evidence.
Advances in technology provide new types of information for scientists.
Advances in technology further prove that viruses have a single common ancestor.

30 .

We know that dogs don't catch the measles from their human companions. Apply your understanding of viruses to make an accurate claim as to why this is so.

Measles is a DNA virus, and DNA viruses cause human diseases.
Dogs do not have glycoproteins.
The measles virus can’t attach to dog cells.
Dogs do not get RNA viruses.

31 .

The Baltimore classification system groups viruses according to how the mRNA is produced. When classified this way, the viruses in each group _____.

behave in a similar manner
look very similar
connect with living things
are based on the type of disease they cause

32 .

Researchers have been able to develop a variety of anti-HIV drugs, such as the drug AZT. How does the drug AZT work?

AZT blocks the enzyme called HIV protease, which the virus uses to reproduce itself.
AZT blocks the HIV integrase enzyme, which the virus uses to insert its viral DNA into the DNA of the host cell.
AZT prevents reverse transcriptase and HIV protease enzyme from functioning inside the body.
AZT prevents reverse transcriptase from making DNA from the viral RNA genome.

33 .

Compare the lytic and lysogenic reproductive cycles of viruses. Provide reasoning to make a case for which cycle has the potential to produce the most virions.

The lytic cycle can theoretically produce more virions, as the viral genome is incorporated into the host cell’s genome replicating along with the host cell.
The lysogenic cycle can theoretically produce more virions, as the reproductive cycle of viruses undergoing lysogeny is much faster than the reproductive cycle of viruses following the lytic cycle.
The lysogenic cycle can theoretically produce more virions, as the viral genome is incorporated into the host cell’s genome and is replicated along with the host cell.
The lytic cycle can theoretically produce more virions, as the prophage following the lysogenic cycle ultimately gets excised from the host cell’s genome and enters the lytic cycle.

34 .

Demonstrate your understanding of viral infections by answering the following: Would a person who has never been in contact with the varicella-zoster virus be at risk of developing chickenpox or shingles if they come in close contact with a person with shingles? Explain your reasoning.

The person would be at risk of developing chickenpox. Chickenpox is the first infection with the virus before it enters latency in the host.
The person would be at risk of developing shingles. Shingles is the first infection with the virus before it enters latency in the host.
The person would be at risk of developing chickenpox. Chickenpox is the first infection with the virus that is already latent in the body.
The person would be at risk of developing shingles. The virus enters the person and gets activated when a person with shingles comes in close contact.

35 .

Which step in the replication cycle of viruses do you think is most critical for the virus to infect cells? Explain why.

The attachment step is the most critical, as infection cannot begin if virus does not attach to the host cell.
The replication step is the most critical as this step directs protein synthesis.
The assembly step is the most critical because new virions are assembled to infect cells.
The entry step is the most critical as nucleic acid of virus needs to enter the host cell naked, leaving the capsid outside.

36 .

For most people, the measles virus does not cause a serious illness. Symptoms include fever and a rash, but the symptoms are usually gone in about a week. However, for some, the measles virus can be much more serious. How can the measles virus cause a potentially fatal illness?

Measles can cause meningococcal disease, which causes severe headaches, seizures and in severe cases can be life-threatening.
Measles can cause variant Creutzfeldt–Jakob disease, which causes severe headaches, seizures and in severe cases can be life-threatening.
Measles can cause encephalitis/meningitis, which causes severe headaches, seizures and in severe cases can be life-threatening.
Measles can cause Legionnaires’ disease, which causes severe headaches, seizures and in severe cases can be life-threatening.

37 .

(credit: modification of work by Rafael Sanjuán, et al./Journal of Virology)

The graph shows the mutation rates of different viruses and bacteria. The ss stands for single strand, ds for double strand, and retro for retroviruses (RNA viruses which transcribe DNA and add it to host's DNA).

Note the viroids at the top left of the graph. These particles infect flowering plants. Based on the trends in this graph, make a prediction about viroid structure.

Viroids have comparatively large sizes and complex genomes.
Viroids have large sizes, but have tiny genomes.
Viroids have a large genome packed in a small structure.
Viroids have small genomes and are extremely small.

38 .

(credit: modification of work by Rafael Sanjuán, et al./Journal of Virology)

The graph shows the mutation rates of different viruses and bacteria. The ss stands for single strand, ds for double strand, and retro for retroviruses (RNA viruses which transcribe DNA and add it to host's DNA).

The SARS-CoV-2 virus that caused the 2020 pandemic is a single stranded RNA virus with positive polarity (ss+RNA). Its mutation rate is comparatively low, when considering ss(+)RNA viruses.

Based on the patterns you see in the graph, make a prediction about the genome size of the SARS-CoV-2.

It has a genome size between 100 and 1,000 nt, most likely closer to 1,000 nt.
It has a genome size between between 1,000 and 10,000 nt, most likely around 5,000 nt.
It has a genome size between slightly below 10,000 nt.
It has a genome size between above 10,000 nt.

39 .

Prions are responsible for variant CJD (Creutzfeldt Jakob Disease). How has this disease been documented to spread from human to human?

Surgery with instruments previously used in a patient with vCJD that were not adequately sterilized and contaminated pineal growth hormones taken from human pineal glands from infected cadavers.
Through human consumption of infected meat and contaminated pituitary growth hormones taken from human pituitary glands from infected cadavers.
Surgery with instruments previously used in a patient with vCJD that were not adequately sterilized and contaminated pituitary growth hormones taken from human pituitary glands from unwell individuals.
Surgery with instruments previously used in a patient with vCJD that were not adequately sterilized and contaminated pituitary growth hormones taken from human pituitary glands from infected cadavers.

40 .

(credit: modification of work by Megansimmer/The Science Creative Quarterly)

The image shows two proteins involed in the bovine spongiform encephalopathy (BSE, the mad cow disease). The protein on the left is healthy. The protein on the right is accumulating extra plated sheets, which cause it to become nonfunctional.

What agent would be causing this fold on the protein?

Bacteria.
Viruses.
Viroids.
Prions.

41 .

Refer to Figure 21.18

.

Review the image of a prion and the brain tissue that it has infected. Apply your understanding of prions to select the best answer to the following: Why is the transmission of a prion not reliant upon genes made of DNA or RNA?

DNA or RNA, though present, is not transmitted when a prion causes infection.
The prion does not contain any DNA or RNA.
Only parts of DNA or RNA are transmitted in a prion.
Far more protein than DNA or RNA is transmitted in a prion.

Critical Thinking Questions