Question 1

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

Accepted Answer

They can only replicate inside living host cells because they lack the cellular machinery for independent metabolism and reproduction.

Question 2

A scientist observes a virus with a hollow, rod-shaped capsid under the electron microscope. Which virus morphology is being observed, and which disease is a classic example?

Accepted Answer

Helical morphology; Ebola virus

Question 3

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

Accepted Answer

They are carbohydrate-protein complexes that allow the virus to attach to specific host cell receptors.

Question 4

A patient is diagnosed with a persistent viral infection that gradually worsens over years and is ultimately fatal. Which of the following viruses is most likely responsible?

Accepted Answer

Measles virus (leading to subacute sclerosing panencephalitis)

Question 5

During the lytic cycle of a bacteriophage, which step immediately follows penetration?

Accepted Answer

Biosynthesis

Question 6

A virus is found to have a double-stranded DNA genome, is nonenveloped, and causes respiratory infections in humans. To which family does this virus most likely belong?

Accepted Answer

Adenoviridae

Question 7

Which laboratory technique would be most appropriate for identifying a virus based on its unique genetic sequence?

Accepted Answer

Polymerase Chain Reaction (PCR)

Question 8

A retrovirus infects a human cell. Which enzyme does it use to convert its RNA genome into DNA, and what is the resulting DNA called once integrated into the host genome?

Accepted Answer

Reverse transcriptase; provirus

Question 9

Which of the following best explains why influenza viruses require a new vaccine formulation each year?

Accepted Answer

Their segmented RNA genome allows for frequent genetic reassortment, leading to new antigenic variants.

Question 10

A virus is described as having a polyhedral capsid, being nonenveloped, and causing warts in humans. Which family does it belong to?

Accepted Answer

Papovaviridae

Question 11

Which of the following is a key difference between the lytic and lysogenic cycles of bacteriophage infection?

Accepted Answer

The lysogenic cycle involves integration of viral DNA into the host genome as a prophage, while the lytic cycle results in immediate host cell lysis.

Question 12

A patient presents with a 'slapped-cheek' rash. Which viral family is most likely responsible, and what is the nature of its genome?

Accepted Answer

Parvoviridae; single-stranded DNA

Question 13

Which of the following best describes the role of the S (spike) protein in coronaviruses?

Accepted Answer

It determines host tropism by mediating attachment to specific host cell receptors.

Question 14

A virus is found to be transmitted from bats to humans, causing a new disease outbreak. What is the term for this type of disease transmission?

Accepted Answer

Zoonotic disease

Question 15

Which of the following equations correctly represents the basic reproductive number ($$R_0) $$and its implications for disease spread?

Accepted Answer

$$R_0$$ \u003e 1$$ means the disease will spread rapidly, R_0$ = 1$$ means it will remain stable, and $$R_0$$ \u003c 1$$ means it will die out.

Question 16

A laboratory is producing influenza vaccines. Which method is most commonly used for mass production of these viruses?

Accepted Answer

Injection into embryonated chicken eggs

Question 17

Which of the following best describes the process of specialized transduction?

Accepted Answer

A prophage excises from the host genome and accidentally carries adjacent host DNA to a new cell.

Question 18

Which of the following is true regarding prions and the diseases they cause?

Accepted Answer

Prions are infectious proteins that cause spongiform encephalopathies by inducing abnormal folding of normal proteins.

Question 19

A plant virus is found to be transmitted by aphids. What is the most likely route of entry for this virus into the plant?

Accepted Answer

Through wounds created by the insect vector

Question 20

Which of the following best explains why a virus with a host range limited to birds might suddenly infect humans?

Accepted Answer

A mutation in the viral spike protein allows it to bind to human cell receptors, expanding its host tropism.

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

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