Q: Which of the following equations correctly represents the calculation of the number of plaque-forming units (PFU) per mL in a bacteriophage sample?

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

Question 1

Which of the following statements best differentiates a virus from a bacterium?

Accepted Answer

Viruses are inert outside of living host cells and require host machinery to multiply.

Question 2

A scientist observes a virus with a polyhedral capsid and no envelope. Which of the following best describes the structure of this virus?

Accepted Answer

It has a many-sided capsid made of protein subunits, with no lipid envelope, and contains either DNA or RNA.

Question 3

Which of the following best explains why viruses have a limited host range?

Accepted Answer

Viruses require specific receptor sites on the host cell surface to initiate infection.

Question 4

During the lytic cycle of a bacteriophage, what is the correct sequence of events?

Accepted Answer

Attachment, penetration, biosynthesis, maturation, release

Question 5

Which laboratory technique is most commonly used to quantify bacteriophages in a sample?

Accepted Answer

Plaque method

Question 6

A virus is found to have a helical capsid and causes a disease characterized by hemorrhagic fever. Which virus is this most likely to be?

Accepted Answer

Ebola virus

Question 7

Which of the following best describes the difference between the lytic and lysogenic cycles of bacteriophages?

Accepted Answer

The lytic cycle results in host cell lysis and release of new phages, while the lysogenic cycle involves integration of viral DNA as a prophage and host cell survival.

Question 8

Which of the following is a key feature of enveloped animal viruses during the release stage?

Accepted Answer

They bud out of the host cell, acquiring a portion of the host membrane as their envelope.

Question 9

A patient presents with recurring cold sores, but no symptoms are present between outbreaks. Which type of viral infection does this represent?

Accepted Answer

Latent infection

Question 10

Which of the following best explains how prions cause disease?

Accepted Answer

By causing abnormal folding of normal cellular proteins, leading to brain degeneration

Question 11

Which of the following equations correctly represents the calculation of the number of plaque-forming units (PFU) per mL in a bacteriophage sample?

Accepted Answer

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

Question 12

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

Accepted Answer

Viroids are small, naked RNA molecules that infect plants and lack a protein coat.

Question 13

A researcher is culturing animal viruses and needs a system that allows for indefinite propagation of the virus. Which type of cell line should be used?

Accepted Answer

Continuous cell line

Question 14

Which of the following best describes the biosynthesis location for DNA and RNA animal viruses?

Accepted Answer

DNA viruses synthesize nucleic acids in the nucleus; RNA viruses synthesize nucleic acids in the cytoplasm.

Question 15

Which of the following is a real-world example of a persistent viral infection?

Accepted Answer

Cervical cancer caused by human papillomavirus

Question 16

Which of the following best explains why lysogenic conversion is medically significant?

Accepted Answer

It can result in the host cell acquiring new properties, such as toxin production.

Question 17

Which of the following is a correct statement about the structure of a complex virus?

Accepted Answer

It has a capsid with additional structures such as a tail sheath and baseplate, as seen in bacteriophages.

Question 18

A patient is diagnosed with subacute sclerosing panencephalitis (SSPE), a rare complication of measles. Which type of viral infection does this represent?

Accepted Answer

Persistent infection

Question 19

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

Accepted Answer

They facilitate attachment of the virus to specific host cell receptors.

Question 20

Which of the following is a correct statement about the replication of a DNA-containing animal virus?

Accepted Answer

The viral DNA enters the host nucleus, where it is replicated and transcribed into mRNA.

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

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