Q: Which equation would you use to calculate the viral titer in a plaque assay if you counted 50 plaques on a plate inoculated with 0.1 mL of a 10^-5 dilution?

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

Question 1

Which of the following best describes why RNA viruses tend to mutate more rapidly than DNA viruses?

Accepted Answer

RNA polymerases lack proofreading capabilities, leading to higher mutation rates.

Question 2

A virus with a helical capsid, an envelope, and a segmented negative-sense RNA genome is most likely classified in which viral family?

Accepted Answer

Orthomyxoviridae

Question 3

Which step in the animal virus replication cycle is unique to animal viruses and not found in bacteriophage replication?

Accepted Answer

Uncoating

Question 4

A patient is diagnosed with a persistent viral infection that periodically flares up with symptoms, followed by long periods with no symptoms. Which virus is most likely responsible?

Accepted Answer

Herpes simplex virus (HSV)

Question 5

Which of the following best explains the process of antigenic shift in influenza viruses?

Accepted Answer

Reassortment of genome segments when two different strains coinfect a host cell

Question 6

Which laboratory method is most appropriate for quantifying the number of infectious bacteriophages in a sample?

Accepted Answer

Plaque assay

Question 7

Which of the following antiviral drugs acts by inhibiting the release of influenza virions from the host cell surface?

Accepted Answer

Oseltamivir

Question 8

A virus is described as having a single-stranded, positive-sense RNA genome. Which statement about its replication is correct?

Accepted Answer

Its genome can be directly translated by host ribosomes.

Question 9

Which of the following is a medically important consequence of phage conversion in bacteria?

Accepted Answer

Bacteria may acquire genes encoding toxins, increasing their pathogenicity.

Question 10

Which of the following best describes a prion?

Accepted Answer

An infectious protein that lacks genetic material

Question 11

Which equation would you use to calculate the viral titer in a plaque assay if you counted 50 plaques on a plate inoculated with 0.1 mL of a 10^-5 dilution?

Accepted Answer

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

Question 12

Which of the following is a key difference between enveloped and naked viruses in their release from host cells?

Accepted Answer

Enveloped viruses are released by budding, while naked viruses are released by cell lysis.

Question 13

A patient is exposed to a virus and receives a laboratory-prepared mixture of antibodies to prevent infection. This is an example of:

Accepted Answer

Postexposure prophylaxis

Question 14

Which of the following best explains why ELISA tests may fail to detect a viral infection during the early stages?

Accepted Answer

The patient has not yet produced detectable levels of antibodies (seroconversion window).

Question 15

Which of the following viruses is known to be oncogenic and associated with human cancers?

Accepted Answer

Human papillomavirus (HPV)

Question 16

Which of the following statements about prion diseases is correct?

Accepted Answer

They are caused by misfolded proteins and can be inherited or acquired.

Question 17

Which of the following best describes the role of viral spikes (peplomers)?

Accepted Answer

They are glycoprotein extensions that help viruses attach and gain entry to host cells.

Question 18

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

Accepted Answer

Attachment → Penetration → Replication → Assembly → Release

Question 19

Which of the following best explains why viruses are considered obligate intracellular pathogens?

Accepted Answer

They require host cell machinery to replicate and produce new virions.

Viruses and Prions: Structure, Classification, Replication, and Clinical Principles

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