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Principles of Medical Virology Quiz
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How do susceptibility and permissiveness differ for a productive viral infection?
- A Susceptible cells express the viral receptor, whereas permissive cells produce antibody against the virus You picked ✕
- B Susceptible cells produce new virions, whereas permissive cells express the viral receptor You picked ✕
- C Susceptible cells undergo lysis, whereas permissive cells allow attachment to the cell surface You picked ✕
- D Susceptible cells allow viral entry, whereas permissive cells support full replication You picked ✓
- E Susceptible cells support genome replication, whereas permissive cells allow viral entry You picked ✕
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Incorrect
The answer is D: Susceptible cells allow viral entry, whereas permissive cells support full replication
Explanation
Why D is correct
See Virion Without a Factory. Option D is correct because the two words describe two separate hurdles a virus must clear. A susceptible cell carries the receptor (the surface molecule the virus attaches to), so the virus can dock and get in. A permissive cell then provides the machinery and conditions inside the cell that the virus needs to replicate, such as ribosomes, energy and building blocks. A cell that is both susceptible and permissive allows the complete cycle and releases new virus. If a cell is susceptible but not permissive, the virus enters but the cycle stalls and no infectious progeny (new virus particles) appear. This is why a virus may attach to many cell types but multiply productively in only a few, and it is why the same virus can be dangerous in one tissue and harmless in another. Memory aid: susceptible is the door, permissive is the factory.
- Susceptible: the cell carries the receptor, so the virus can dock and get in.
- Permissive: the cell supplies the machinery and conditions inside it that the virus needs to replicate.
- Outcome: a susceptible cell that is not permissive lets the virus enter but yields no infectious progeny.
Why the other options are incorrect
- A. Susceptible cells express the viral receptor, whereas permissive cells produce antibody against the virus: Antibody production is a function of B cells and plasma cells in the immune system, not a definition of a permissive cell. Permissiveness describes whether the cell supports viral replication. Your answer
- B. Susceptible cells produce new virions, whereas permissive cells express the viral receptor: Producing new virions requires a cell to be both susceptible and permissive, not susceptible alone. Receptor expression is the hallmark of susceptibility, not permissiveness. Your answer
- C. Susceptible cells undergo lysis, whereas permissive cells allow attachment to the cell surface: Lysis is one possible release outcome for some viruses, not the meaning of susceptibility. Attachment to the cell surface depends on receptor expression, which defines susceptibility. Your answer
- E. Susceptible cells support genome replication, whereas permissive cells allow viral entry: This reverses the two terms. Entry depends on the receptor and therefore defines susceptibility, while supporting genome replication is a feature of permissiveness. Your answer
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