Q: Which equation best represents the calculation of plaque-forming units (PFU) in a viral plaque assay?

$PFU = \frac{\text{Number of plaques}}{\text{Dilution factor} \times \text{Volume plated (mL)}}$

Question 1

Which of the following statements best distinguishes viruses from prokaryotic and eukaryotic cells?

Accepted Answer

Viruses lack cellular structure and cannot replicate without a host cell.

Question 2

A scientist is studying the influenza virus and observes changes in its surface proteins over several years. Which process is most likely responsible for these changes?

Accepted Answer

Antigenic drift, which involves gradual mutations in viral genes encoding surface proteins.

Question 3

Which component of a virus is responsible for recognizing and binding to specific host cells, thereby determining host range and tropism?

Accepted Answer

Surface spikes (glycoproteins)

Question 4

A bacteriophage infects a bacterial cell and immediately begins producing new phage particles, leading to cell lysis. Which type of replication cycle is this?

Accepted Answer

Lytic cycle

Question 5

During the lysogenic cycle of a bacteriophage, what happens to the viral genome?

Accepted Answer

It integrates into the host bacterial chromosome and is replicated along with it.

Question 6

Which of the following best explains how antigenic shift can lead to influenza pandemics?

Accepted Answer

Antigenic shift occurs when two different influenza viruses infect the same cell and exchange gene segments, creating a novel virus.

Question 7

Which equation best represents the calculation of plaque-forming units (PFU) in a viral plaque assay?

Accepted Answer

$PFU = \frac{	ext{Number of plaques}}{	ext{Dilution factor} 	imes 	ext{Volume plated (mL)}}$

Question 8

Which of the following is a key difference between acute and latent viral infections in animals?

Accepted Answer

Acute infections result in rapid onset of symptoms and virus clearance, while latent infections involve periods of dormancy with possible reactivation.

Question 9

Which of the following best describes the role of selective pressure in viral evolution?

Accepted Answer

Selective pressure favors viral variants that can evade host immune responses, leading to the spread of advantageous genes.

Question 10

A bacteriophage is grown in a laboratory using a bacterial lawn. What is the purpose of a plaque assay in this context?

Accepted Answer

To determine the number of infectious phage particles present in a sample.

Question 11

Which of the following antiviral drugs inhibits viral DNA synthesis by acting as a nucleoside analog?

Accepted Answer

Acyclovir

Question 12

Which structure is NOT found in all viruses?

Accepted Answer

Envelope

Question 13

Which of the following best describes the function of the viral capsid?

Accepted Answer

It protects the viral genome and aids in attachment to host cells.

Question 14

Which process allows a bacteriophage to transfer bacterial genes from one cell to another?

Accepted Answer

Transduction

Question 15

A patient is infected with a virus that only infects liver cells. This specificity is an example of:

Accepted Answer

Tropism

Question 16

Which of the following is TRUE regarding the replication of animal viruses?

Accepted Answer

Some animal viruses require fusion with the host cell membrane for entry.

Question 17

Which of the following is a consequence of antigenic drift in influenza viruses?

Accepted Answer

Gradual changes in viral surface proteins, leading to seasonal outbreaks.

Question 18

Which of the following is NOT a function of viral surface spikes?

Accepted Answer

Catalyzing viral genome replication.

Question 19

Which of the following best describes the genetic material found in viruses?

Accepted Answer

Viruses may contain either DNA or RNA, which can be single- or double-stranded.

Question 20

Which of the following scenarios best illustrates the concept of host range in viruses?

Accepted Answer

A virus that infects only humans but not other mammals.

Study Guide: Viruses, Bacteriophages, and Viral Replication

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