Question 1

Antiviral drugs are often diﬃcult to develop, largely because ________.

Accepted Answer

Viruses are obligate intracellular parasites, meaning they must infect and operate within host cells to replicate. Developing antiviral drugs that can target the virus without harming the host cells is challenging, often leading to toxic side effects.

Question 2

How are viroids transmitted?

Accepted Answer

Viroids are primarily transmitted through plant seeds as well as through mechanical means such as contaminated tools and by grafting from an infected plant to a healthy one. They are pathogenic to plants and do not infect animals, hence they are not transmitted through respiratory secretions, sex, or blood products.

Question 3

Sterilizing ﬁlters have a pore size of 0.22 μm. Which of the following statements is true?

Accepted Answer

Bacterial cells, which are typically between 1-10 μm in size, are larger than the 0.22 μm pore size of sterilizing filters and are therefore blocked. Most viruses, however, range from 20 to 200 nm in size and can pass through these filters.

Question 4

Why do some animal viruses have an external envelope, while bacteriophages never do?

Accepted Answer

Animal viruses can acquire an envelope from the host cell's plasma membrane when they bud out, while bacteriophages, which infect bacteria, typically exit the host cell by lysing it, not by budding, hence they do not acquire an envelope.

Question 5

You are working in a laboratory that is studying a newly isolated virus. Your job is to culture the virus using in vitro methods. Upon observing your inoculated tissue culture specimen one day, you notice clumps of cells growing on top of the original monolayer of cells. Microscopic analysis of stained cells from the culture reveal an alteration in host cell membrane protein content and chromosomal structure. Based upon this information, you hypothesize that the virus you are studying is ______.

Accepted Answer

The observed alterations in host cell membrane protein content and chromosomal structure, along with the formation of cell clumps on top of the original monolayer, suggest the virus is causing transformation of the host cells. This is characteristic of oncoviruses, which are viruses that can cause cancer.

Question 6

Compared to bacteria that have a typical size range between 1-10 μm, _______.

Accepted Answer

Viruses have a much greater size range compared to bacteria, with sizes varying between 22 nm and 1000 nm. This makes them generally smaller than bacterial cells, which are typically between 1-10 μm in size.

Question 7

A treatment for bacterial infections from the early 20th century has made a comeback; the use of bacterial viruses to eliminate bacterial infections. Which explanation most accurately describes the reason for the return of this treatment?

Accepted Answer

Antibiotic resistance has become a significant challenge in treating bacterial infections, leading to a renewed interest in bacteriophage therapy as an alternative to traditional antibiotics.

Question 8

In order to replicate within a host cell, a virus with a genome comprised of single-stranded positive- sense RNA _______.

Accepted Answer

The answer of In order to replicate within a host...

Question 9

Tami?u is a common medication given for in?uenza treatment. It works by protecting and blocking sialic acid molecules on the surfaces of host cells and in?uenza virus envelopes as they leave the cell. Which statement re?ects the mechanism of Tami?u's action?

Accepted Answer

Tami?u (oseltamivir) works by inhibiting the neuraminidase enzyme on the surface of the influenza virus. This enzyme is crucial for the release of newly formed virus particles from infected cells, thereby preventing the virus from spreading within the body.

Question 10

In order to synthesize proteins, a virus with a genome comprised of single-stranded negative-sense RNA _______.

Accepted Answer

Viruses with single-stranded negative-sense RNA genomes must first use that strand as a template to synthesize a complementary positive-sense RNA strand, which can then be used as mRNA for protein synthesis.

Question 11

Select the statement that most accurately describes the action of antimicrobial drugs today.

Accepted Answer

Antiviral drugs can indeed cause toxic side effects because they target viral processes that often occur within host cells, leading to potential damage or interference with the host's normal cellular functions. This is a significant challenge in antiviral drug design and use.

Question 12

Using species names for viruses is controversial since viruses are not considered living organisms, and they change over time so characteristics that may be used for speciation are unstable.

Accepted Answer

Viruses are not considered living organisms, so using species names for them is controversial. Additionally, viruses change over time, making characteristics used for speciation unstable.

Question 13

Viral nomenclature uses the same system as living organisms; a genus and speci?c epithet is designated for each virus.

Accepted Answer

Viral nomenclature does not follow the binomial system (genus and specific epithet) used for living organisms. Instead, viruses are classified based on their properties and grouped into families and genera, but their names do not follow the same structured format as plants and animals.

Question 14

Successful anti-HIV drug therapies today work by blocking the action of viral reverse transcriptase. Select which step of virus multiplication that would be directly blocked by this mechanism.

Accepted Answer

Synthesis is directly blocked by anti-HIV drugs that target viral reverse transcriptase, as these drugs prevent the virus from synthesizing DNA from its RNA template, a crucial step in the viral replication process.

Question 15

Viral classiﬁcation has changed over the years and while they are given genus names, the use of species names has not been widely accepted. This is because ________.

Accepted Answer

All of these choices (A, B, and C) are valid arguments against using species designations for viruses, reflecting the complexities in viral classification due to their non-living status, high mutation rates, and the diversity within what could be considered a single species.

Question 16

Which of the following is a true statement regarding lysogeny?

Accepted Answer

Lysogeny involves the integration of the bacteriophage genome into the host bacterial cell's chromosome, where it can be replicated along with the host's DNA and passed on to daughter cells. This can confer new characteristics to the host cell, such as toxin production, which can be harmful to humans.

Quiz 6: Viruses and Prions