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

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

Question 1

Which of the following characteristics distinguishes viruses from bacteria?

Accepted Answer

Viruses lack ribosomes and do not generate ATP.

Question 2

A scientist is studying a virus that has a lipid envelope, glycoprotein spikes, and a helical capsid. Which of the following best describes how this virus is most likely released from the host cell?

Accepted Answer

By budding from the host cell membrane

Question 3

Which of the following best explains why most viruses infect only specific types of cells in one host?

Accepted Answer

Viral attachment sites must match specific host cell receptors.

Question 4

A nonenveloped polyhedral virus with spikes is most likely to have which of the following structures?

Accepted Answer

A capsid composed of capsomeres with glycoprotein projections

Question 5

Which of the following is the correct taxonomic ending for a viral family?

Accepted Answer

-viridae

Question 6

A researcher is using the plaque method to quantify bacteriophages. What does each plaque on the bacterial lawn represent?

Accepted Answer

A single virus that has lysed a host cell and its descendants

Question 7

Which of the following techniques would be most appropriate to rapidly identify the presence of influenza virus RNA in a patient sample?

Accepted Answer

Polymerase Chain Reaction (PCR)

Question 8

During the lytic cycle of a T-even bacteriophage, which enzyme is responsible for breaking down the bacterial cell wall to release new virions?

Accepted Answer

Phage lysozyme

Question 9

A bacterium acquires the ability to produce a toxin only after infection by a lysogenic phage. What is the best explanation for this phenomenon?

Accepted Answer

Phage conversion due to integration of prophage DNA

Question 10

Which of the following best describes the biosynthesis of a +ssRNA virus?

Accepted Answer

The viral RNA serves directly as mRNA for protein synthesis.

Question 11

Which virus family is associated with double-stranded DNA, an envelope, and the ability to cause skin lesions such as smallpox?

Accepted Answer

Poxviridae

Question 12

A patient presents with cold sores that recur during periods of stress. Which type of infection does this represent?

Accepted Answer

Latent viral infection

Question 13

Which of the following best describes a prion?

Accepted Answer

A misfolded protein that is infectious and causes diseases such as Creutzfeldt-Jakob disease

Question 14

Which of the following equations best represents the calculation of plaque-forming units (PFU) per mL in a viral plaque assay?

Accepted Answer

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

Question 15

Which of the following is a key difference between the multiplication of DNA viruses and RNA viruses in animal cells?

Accepted Answer

DNA viruses typically replicate their genome in the nucleus, while RNA viruses replicate in the cytoplasm.

Question 16

A plant is infected with a pathogen that consists of a short, circular piece of naked RNA. Which of the following is the most likely cause?

Accepted Answer

Viroid

Question 17

Which of the following best explains how a protein can be infectious, as in prion diseases?

Accepted Answer

The misfolded prion protein induces normal proteins to adopt the abnormal conformation.

Question 18

Which of the following best describes specialized transduction?

Accepted Answer

Only specific bacterial genes near the prophage integration site are transferred by a lysogenic phage.

Question 19

A virus is classified as a Retroviridae. Which enzyme is essential for its replication cycle?

Accepted Answer

Reverse transcriptase

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

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