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USMLE Step 1 Virology — practice questions

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 1–30 of 41.

What is a virion?Read the answer and worked solution →Which imaging method is the only one that reveals the internal structures of a virion?Read the answer and worked solution →The protein subunits that build up a viral capsid carry which name?Read the answer and worked solution →Which hypothesis about the origin of viruses proposes that they descend from free-living cells?Read the answer and worked solution →The escapist hypothesis explains the origin of viruses by proposing that they began as what?Read the answer and worked solution →Viruses built with a head and a tail infect which kind of host?Read the answer and worked solution →Which host cell molecule does HIV use as one of its receptors?Read the answer and worked solution →The outer envelope of an enveloped virus is built from membrane taken from where?Read the answer and worked solution →The Baltimore scheme sorts viruses according to which single feature?Read the answer and worked solution →Who developed the most commonly used system of virus classification, and when?Read the answer and worked solution →A single-stranded RNA genome of positive polarity behaves in which way once inside a host cell?Read the answer and worked solution →A double-stranded RNA virus generates its mRNA using which enzyme?Read the answer and worked solution →Tobacco mosaic virus is long and cylindrical, which places it in which shape group?Read the answer and worked solution →What name is given to a cell that a virus is actually able to use for replication?Read the answer and worked solution →Which step of the virus replication cycle comes immediately after penetration?Read the answer and worked solution →When a bacteriophage infects a bacterium, what becomes of the phage capsid?Read the answer and worked solution →Phage DNA that has been incorporated into a bacterial genome carries which name?Read the answer and worked solution →T4 infects Escherichia coli of the human gut and bursts the cell open. Which replication cycle is that?Read the answer and worked solution →Herpes simplex virus can sit silently in nerve tissue for years. Why is that state not called lysogeny?Read the answer and worked solution →Entry by fusion of the viral coat with the plasma membrane is open to which viruses?Read the answer and worked solution →Oncogenic viruses cause cancer by disturbing the host cell cycle in which way?Read the answer and worked solution →Which pairing of virus and cancer is correct?Read the answer and worked solution →Viruses may use which molecule as their genetic material?Read the answer and worked solution →Viral vaccines may be prepared from which three kinds of material?Read the answer and worked solution →What is the particular danger of giving a live attenuated viral vaccine?Read the answer and worked solution →Why must an influenza vaccine be given again before every new season?Read the answer and worked solution →Vaccination given after a bite from a rabid animal can still save the patient because of what?Read the answer and worked solution →A viral protein is a safe drug target only if it has which property?Read the answer and worked solution →Tamiflu treats influenza by inhibiting neuraminidase. What does that enzyme normally do?Read the answer and worked solution →Why does HAART combine several anti-HIV drugs instead of relying on one?Read the answer and worked solution →

Worked practice questions

What is a virion?

  1. A host cell that has just been lysed
  2. A protein subunit that builds a capsid
  3. A viral gene sitting in host DNA
  4. A single virus particle outside a cell
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Correct answer: D. A single virus particle outside a cell

1. A virion is one individual virus particle. 2. It is the infectious form the virus takes while it is outside a host cell. 3. A capsid subunit is a capsomere, and viral DNA inside a host genome is a prophage, so neither of those is a virion. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 21 "Viruses", section 21.1 Viral Evolution, Morphology, and Classification_

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Which imaging method is the only one that reveals the internal structures of a virion?

  1. Scanning electron microscopy
  2. Light microscopy at high power
  3. Transmission electron microscopy
  4. Either light or scanning microscopy
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Correct answer: C. Transmission electron microscopy

1. Both scanning and transmission electron microscopy show the surface structure of virions. 2. Only transmission electron microscopy shows what lies inside the particle. 3. A light microscope cannot resolve viruses at all, apart from some large poxvirus virions. 4. Scanning electron microscopy stops at the outer surface, so it is the trap answer here. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 21 "Viruses", section 21.1 Viral Evolution, Morphology, and Classification_

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The protein subunits that build up a viral capsid carry which name?

  1. Ribosomes
  2. Nucleotides
  3. Capsomeres
  4. Glycoproteins
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Correct answer: C. Capsomeres

1. Every virion carries a nucleic acid genome inside a protective protein layer called the capsid. 2. That capsid is assembled from repeated protein subunits, and each subunit is a capsomere. 3. Glycoproteins sit on the surface for attachment, and ribosomes belong to cells rather than to viruses. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 21 "Viruses", section 21.1 Viral Evolution, Morphology, and Classification_

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