Question 1

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

Accepted Answer

They require host cell metabolic machinery to reproduce.

Question 2

A scientist isolates a virus with a helical capsid and an envelope. Which of the following best describes the structure of this virus?

Accepted Answer

The capsomeres are arranged in a spiral around the nucleic acid, and the virus is surrounded by a phospholipid bilayer.

Question 3

Which of the following is the primary criterion used by scientists to classify viruses?

Accepted Answer

The nature of their genetic material (DNA or RNA)

Question 4

A virus with a single-stranded, positive-sense RNA genome enters a host cell. What is the first step in the synthesis of viral proteins?

Accepted Answer

The +ssRNA acts directly as mRNA and is translated by host ribosomes.

Question 5

Which of the following best describes the process of budding in enveloped animal viruses?

Accepted Answer

The virus acquires its envelope from the host cell membrane as it exits the cell.

Question 6

Which of the following is true regarding prions?

Accepted Answer

They are composed solely of protein and lack nucleic acids.

Question 7

A patient presents with symptoms of a fatal neurological disease. Brain tissue shows spongiform changes and fibril deposition. Which infectious agent is most likely responsible?

Accepted Answer

A prion

Question 8

Which of the following best explains why viruses are not considered alive by some scientists?

Accepted Answer

They cannot reproduce independently outside a host cell.

Question 9

Which of the following is a unique feature of retroviruses such as HIV?

Accepted Answer

They use reverse transcriptase to synthesize DNA from their RNA genome.

Question 10

A plant shows stunted growth and abnormal leaf patterns. Laboratory analysis reveals the presence of a small, circular RNA molecule with no protein coat. What is the most likely infectious agent?

Accepted Answer

A viroid

Question 11

Which of the following steps is unique to the lysogenic cycle of bacteriophages?

Accepted Answer

Integration of viral DNA into the host genome as a prophage

Question 12

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

Accepted Answer

It provides protection for the viral nucleic acid and aids in attachment to host cells.

Question 13

A virus is found to infect both humans and birds, but attaches to different cell types in each host. What property does this virus exhibit?

Accepted Answer

Host specificity due to affinity of viral surface proteins for host cell receptors

Question 14

Which of the following is a correct statement about the synthesis of -ssRNA animal viruses?

Accepted Answer

They carry an RNA-dependent RNA transcriptase to synthesize mRNA from their genome.

Question 15

Which of the following is a plausible reason why prion diseases are so difficult to control in medical settings?

Accepted Answer

Prions are resistant to most sterilization methods and require incineration for destruction.

Question 16

Which of the following best describes the process of viral latency in animal cells?

Accepted Answer

The viral genome remains dormant within the host cell, sometimes integrating into the host chromosome.

Question 17

Which of the following is a correct description of a polyhedral virus?

Accepted Answer

It has a roughly spherical shape with capsomeres arranged in a geodesic dome-like structure.

Question 18

Which of the following equations best represents the burst size in a lytic bacteriophage replication cycle?

Accepted Answer

$$Burst\ size = \frac{Total\ number\ of\ virions\ released}{Number\ of\ infected\ cells}$$

Question 19

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

Accepted Answer

Viroids lack a protein capsid and are composed solely of a short, circular RNA molecule.

Question 20

Which of the following best explains why viral genomes are generally much smaller than cellular genomes?

Accepted Answer

Viruses do not require genes for metabolic pathways or independent replication.

Characterizing and Classifying Viruses, Viroids, and Prions

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