Question 1

Which of the following best describes why viruses are not considered living organisms?

Accepted Answer

They cannot replicate independently outside a host cell.

Question 2

A scientist observes a virus with a rod-shaped structure under the microscope. Which type of symmetry does this virus most likely exhibit?

Accepted Answer

Helical

Question 3

Which enzyme is essential for retroviruses to integrate their genetic material into the host genome, and what is the reaction it catalyzes?

Accepted Answer

Reverse transcriptase; RNA \rightarrow DNA

Question 4

During a plaque assay, a student counts 50 plaques on a plate after plating 0.1 mL of a $$10^{-6}$$ dilution of a viral stock. What is the titer of the original stock in plaque-forming units (PFU) per mL?

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

Accepted Answer

$$5 	imes 10^8$ PFU/mL

Question 5

Which of the following is a correct comparison between naked and enveloped viruses?

Accepted Answer

Naked viruses consist only of nucleic acid and capsid.

Question 6

A patient is infected with a virus that integrates its genome into the host DNA and remains dormant until activated by stress. What is this type of infection called, and what is the integrated viral DNA known as?

Accepted Answer

Lysogenic infection; prophage

Question 7

Which of the following best explains why RNA viruses must carry their own RNA-dependent RNA polymerase in the virion?

Accepted Answer

Host cells lack enzymes to synthesize RNA from an RNA template.

Question 8

Which step in the viral replication cycle is characterized by the assembly of new virions but no detectable extracellular virus?

Accepted Answer

Eclipse phase

Question 9

A bacteriophage infects E. coli and uses LPS receptors for attachment. Which model virus is being described, and what is the mechanism of genome entry?

Accepted Answer

T4 phage; tail sheath contraction and DNA injection

Question 10

Which of the following is a possible outcome of animal virus infection that can lead to cancer?

Accepted Answer

Transformation

Question 11

A plant virus is most likely to enter a host cell by which of the following mechanisms?

Accepted Answer

Entry through wounds or via insect vectors

Question 12

Which of the following best describes the difference in growth curves between viruses and bacteria?

Accepted Answer

Viruses exhibit a one-step growth curve, while bacteria show exponential growth.

Question 13

Which enzyme is responsible for breaking down the bacterial cell wall to allow viral genome entry and virion release?

Accepted Answer

Lysozyme

Question 14

A virus is observed to have a burst size of 200. What does this mean in the context of viral replication?

Accepted Answer

200 virions are released from a single infected cell.

Question 15

Which of the following statements about enveloped viruses is correct?

Accepted Answer

They acquire their lipid membrane from the host cell.

Question 16

Which of the following is NOT a function of viral surface proteins?

Accepted Answer

Genome replication

Question 17

A virus infects a host cell and causes slow, continuous release of new virions without killing the host. What type of infection is this?

Accepted Answer

Persistent

Question 18

Which of the following best explains why enveloped viruses are rare in bacteria and plant viruses?

Accepted Answer

Bacteria and plant cells have rigid cell walls that prevent budding.

Question 19

Which of the following is a correct statement about the viral nucleocapsid?

Accepted Answer

It is composed of the viral genome and the capsid.

Question 20

A virologist is studying a virus with a genome size similar to that of a ribosome. Which virus is most likely being studied?

Accepted Answer

Poliovirus

Viruses: Structure, Replication, and Life Strategies

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