$$\text{Viral titer (PFU/ml)} = \frac{\text{Number of plaques}}{\text{Dilution factor} \times \text{Volume plated (ml)}}$$

Question 1

Which of the following statements best explains why viruses are considered nonliving pathogens?

Accepted Answer

They must invade living cells and hijack cellular machinery to replicate.

Question 2

A virus with a helical capsid and a lipid envelope is most likely to enter a host cell by which mechanism?

Accepted Answer

Fusion with the host cell membrane

Question 3

Which of the following best describes the process of antigenic drift in influenza viruses?

Accepted Answer

Frequent minor mutations in spike proteins that help the virus evade immune detection

Question 4

A bacteriophage that integrates its genome into the host bacterial chromosome and remains dormant is called a:

Accepted Answer

Prophage

Question 5

Which of the following equations correctly represents the calculation of viral titer in a plaque assay?

Accepted Answer

$$	ext{Viral titer (PFU/ml)} = \frac{	ext{Number of plaques}}{	ext{Dilution factor} 	imes 	ext{Volume plated (ml)}}$$

Question 6

Which of the following is a unique feature of prions compared to viruses?

Accepted Answer

They are infectious proteins with no genetic material.

Question 7

A virus with a segmented RNA genome is capable of which evolutionary process that can lead to pandemics?

Accepted Answer

Antigenic shift

Question 8

Which of the following best describes the function of viral spike proteins (peplomers)?

Accepted Answer

They help viruses attach to specific features on host cells.

Question 9

Which of the following is a correct statement about the Baltimore classification system?

Accepted Answer

It groups viruses by their genome type, strandedness, sense, and replication method.

Question 10

A patient is diagnosed with a latent viral infection. Which of the following best describes the infection?

Accepted Answer

The virus alternates between periods of dormancy and flare-ups with symptoms.

Question 11

Which of the following is a potential outcome of phage conversion in bacteria?

Accepted Answer

The bacterium gains new pathogenic properties, such as toxin production.

Question 12

Which of the following best explains why RNA viruses mutate more rapidly than DNA viruses?

Accepted Answer

RNA polymerases lack proofreading capabilities.

Question 13

Which of the following is a correct sequence of steps in the lytic replication cycle of a bacteriophage?

Accepted Answer

Attachment, Penetration, Replication, Assembly, Release

Question 14

Which of the following laboratory techniques is most appropriate for detecting very low levels of viral genetic material in a clinical sample?

Accepted Answer

Molecular methods such as PCR

Question 15

Which of the following best describes the role of reverse transcriptase in retroviruses?

Accepted Answer

It synthesizes DNA from an RNA template.

Question 16

A virus is described as having a naked icosahedral capsid. Which of the following is true about this virus?

Accepted Answer

It lacks an envelope and relies on its capsid for protection.

Question 17

Which of the following is a reason why antigenic shift in influenza viruses is particularly concerning for public health?

Accepted Answer

It can produce new viral strains with increased infectivity or expanded host range.

Question 18

Which of the following best describes the difference between acute and chronic viral infections?

Accepted Answer

Acute infections are cleared by the immune system, while chronic infections involve continuous release of virions over time.

Question 19

Which of the following is a correct statement about the cultivation of animal viruses?

Accepted Answer

They are often grown using tissue culture techniques.

Viruses and Prions: Structure, Classification, Replication, and Pathogenesis

Study Guide - Practice Questions