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USMLE Step 1 Virology — practice questions — page 2

Explore 41 free Virology questions in USMLE Step 1 Microbiology. Open each question or exercise to read its content, reference answers and available explanation.

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Virology questions and exercises with answers

Showing questions 31–41 of 41.

Which class of anti-HIV drug blocks the insertion of viral DNA into the host genome?Read the answer and worked solution →Which molecule is completely absent from a prion?Read the answer and worked solution →How does an incoming PrPsc molecule multiply itself inside the body?Read the answer and worked solution →Kuru spread among people in Papua New Guinea through which practice?Read the answer and worked solution →Viroids are best described as which kind of infectious particle?Read the answer and worked solution →What does a viroid produce inside the plant cell it has infected?Read the answer and worked solution →Run the virus replication cycleRead the answer and worked solution →Sort viruses by genome chemistryRead the answer and worked solution →Enveloped or naked?Read the answer and worked solution →Name the virology termRead the answer and worked solution →Spot the false virology claimRead the answer and worked solution →

Worked practice questions

Which class of anti-HIV drug blocks the insertion of viral DNA into the host genome?

  1. Fusion inhibitors
  2. Protease inhibitors
  3. Integrase inhibitors
  4. Neuraminidase blockers
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Correct answer: C. Integrase inhibitors

1. Anti-HIV drugs are grouped by which phase of the replicative cycle they block. 2. Fusion inhibitors block the viral envelope from fusing with the host plasma membrane. 3. Reverse transcriptase inhibitors block conversion of the RNA genome into double-stranded DNA. 4. Integrase inhibitors block integration of that viral DNA into the host genome, which is what the question asks for. 5. Protease inhibitors act later still, on the processing of viral proteins. 6. Neuraminidase is an influenza target rather than an HIV one, so that option belongs to another virus. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 21 "Viruses", section 21.3 Prevention and Treatment of Viral Infections_

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Which molecule is completely absent from a prion?

  1. Any folded protein
  2. Any amino acid chain
  3. Any sugar residue
  4. Any nucleic acid
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Correct answer: D. Any nucleic acid

1. A prion is an infectious particle made of protein. 2. It replicates without DNA and without RNA, so it carries no nucleic acid at all. 3. That is why it was long thought impossible for such an agent to exist. 4. Protein is the one thing a prion is built from, so the protein options are the opposite of the answer. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 21 "Viruses", section 21.4 Other Acellular Entities: Prions and Viroids_

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How does an incoming PrPsc molecule multiply itself inside the body?

  1. It is copied by a host RNA polymerase
  2. It splits in two like a bacterial cell
  3. It binds PrPc and converts it to PrPsc
  4. It orders ribosomes to make more PrPsc
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Correct answer: C. It binds PrPc and converts it to PrPsc

1. The prion protein PrP exists in two forms, the normal PrPc and the infectious PrPsc. 2. Once introduced into the body, the PrPsc inside the prion binds to PrPc. 3. Binding converts that normal molecule into the infectious form. 4. Each new PrPsc can convert another PrPc, so the amount rises exponentially and the protein aggregates. 5. PrPsc is folded abnormally, and that shape is directly responsible for the brain lesions. 6. No polymerase and no ribosome is involved, since the prion carries no gene of its own, which rules out two options. 7. Splitting in two is cell division, and a protein particle cannot divide, so that option is not possible. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 21 "Viruses", section 21.4 Other Acellular Entities: Prions and Viroids_

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