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

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

Question 1

Which of the following best describes the difference between a virus and a virion?

Accepted Answer

A virus is the intracellular form that hijacks host machinery, while a virion is the complete extracellular particle.

Question 2

A scientist is studying a virus that infects only plant cells and consists solely of a short strand of RNA without a protein coat. Which type of infectious agent is this?

Accepted Answer

Viroid

Question 3

Which of the following statements about prions is correct?

Accepted Answer

Prions are infectious misfolded proteins that cause aggregation and neural damage.

Question 4

A virus with a rod-shaped capsid structure is classified as which type?

Accepted Answer

Helical

Question 5

During the lytic cycle of bacteriophage replication, which step directly follows the assembly of new virions?

Accepted Answer

Lysis of the host cell

Question 6

Which viral component is responsible for attachment to host cells and is often found on the viral envelope?

Accepted Answer

Spike protein

Question 7

A patient is diagnosed with Creutzfeldt-Jakob disease. Which molecular abnormality is most directly responsible for this condition?

Accepted Answer

Aggregation of PrPsc, the abnormal prion protein

Question 8

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

Accepted Answer

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

Question 9

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

Accepted Answer

They require host cell machinery to replicate their genome and assemble new virions.

Question 10

A virus is described as enveloped, segmented RNA, and uses HA and NA proteins for attachment and release. Which virus fits this description?

Accepted Answer

Influenza A

Question 11

Which step is unique to the lysogenic cycle of bacteriophage replication compared to the lytic cycle?

Accepted Answer

Integration of viral genome into the host chromosome

Question 12

A virus is found to have a polyhedral capsid, is non-enveloped, and replicates in the nucleus. Which virus is most likely being described?

Accepted Answer

HPV

Question 13

Which of the following is true regarding viral host range?

Accepted Answer

Viruses typically have a limited host range, infecting only specific cell types.

Question 14

A researcher observes clear zones on a bacterial lawn after exposure to a virus. What is the most likely explanation for these clear zones?

Accepted Answer

Viral infection has caused lysis of bacterial cells, forming plaques.

Question 15

Which of the following best describes the function of reverse transcriptase in HIV replication?

Accepted Answer

It converts viral RNA into DNA for integration into the host genome.

Question 16

A virus is classified as a viral species if it shares which of the following characteristics?

Accepted Answer

Genetic information and host range

Question 17

Which of the following is a correct description of the viral envelope?

Accepted Answer

It is derived from the host cell membrane and may contain spike proteins.

Question 18

A virus infects T cells, integrates its genome as a provirus, and buds from the host cell. Which virus is being described?

Accepted Answer

HIV

Question 19

Which of the following best explains why the 1918 Spanish flu pandemic was so deadly?

Accepted Answer

The virus was an enveloped, segmented RNA virus capable of rapid genetic reassortment.

Question 20

A virus is described as having a complex capsid structure. Which type of virus is most likely being referred to?

Accepted Answer

Bacteriophage

Viruses, Viroids, and Prions – Study Guide

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