Which is true of the eclipse phase?
Answer: D
The genome has been uncoated and exposed to the machinery that will express it, so the intact parental particle no longer exists and progeny have not yet been assembled. Recoverable virus returns once maturation begins.
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Which event marks the end of the multiplication cycle?
Answer: A
Correct answer: Egress
Egress is the release of the progeny from the cell, by lysis for a naked virus or by budding for an enveloped one, and it completes the cycle by making the particles available to infect further cells. Attachment, penetration and uncoating are the opening steps, so the cycle runs from one attachment to the next.
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The receptor a virus binds is located on the
Answer: B
The receptor belongs to the cell and the anti-receptor to the virus, so binding brings the two surfaces together. Because the receptor is a normal cell constituent, its distribution across tissues shapes which organs a virus can affect.
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Which of these is NOT a route by which a virus penetrates a cell?
Answer: C
Binary fission is how a bacterium divides, not how anything enters a cell. Penetration proceeds by endocytosis, by fusion of a viral envelope with a cell membrane, or by direct translocation, and all three require energy.
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A virus that infects only one species is described as having
Answer: D
Correct answer: a narrow host range
Host range is set chiefly by whether a cell carries a receptor the virus can bind, and secondarily by whether it can support the later stages of the cycle. A virus restricted to one species has a narrow range - and the narrowness matters for eradication, since a pathogen with no animal reservoir, as smallpox had none, can in principle be eliminated entirely.
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Which best describes viral tropism?
Answer: A
Tropism is the preference of a virus for particular cells or tissues, and it usually traces back to receptor distribution together with whether the cell supports the rest of the cycle. It explains why one virus causes hepatitis and another a respiratory illness.
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Which is a valid reason a cell may resist infection despite carrying the receptor?
Answer: B
Correct answer: It may not support a later stage of the cycle
Carrying the receptor makes a cell susceptible, but permissiveness is a separate matter: the cell must also supply whatever polymerases, transcription factors and processing enzymes the virus needs. A susceptible but non-permissive cell can be entered and yet yield no progeny, which is precisely the abortive infection described elsewhere in this topic.
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Which term describes the complete set of steps from attachment to egress?
Answer: C
The multiplication or replication cycle covers the whole sequence in a single infected cell. The eclipse is one interval within it, while a plaque assay and cytopathic effect are ways of observing that it has happened.
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Progeny virions accumulate at exponential rates during
Answer: D
Correct answer: maturation
Maturation is the assembly of the synthesised components into complete particles, so it is during this phase that infectious virus reappears in the cell and accumulates rapidly. Before it lies the eclipse phase, during which the genome and proteins are being made but no infectious particle can be recovered - which is why the yield curve stays flat and then rises steeply.
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