The genome of a poxvirus is
Answer: A
Poxviruses carry double-stranded DNA of 130 to 260 kilobases, the parapoxviruses at the lower end and fowlpox at the upper. That is a very large genome for a virus, and it is what allows the family to encode the enzymes it needs to replicate away from the nucleus.
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The genome size of poxviruses is approximately
Answer: B
The range runs from about 130 kilobases in the parapoxviruses to about 260 in fowlpox. A genome of that size can encode well over a hundred proteins, including the transcription machinery the virus carries into the cell.
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Poxvirus particles are described as
Answer: C
The characteristic form is a brick roughly 240 by 300 nanometres, which makes poxviruses among the largest animal viruses and large enough to be glimpsed by light microscopy. Parapoxviruses are narrower and ovoid rather than brick-like.
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The approximate dimensions of a poxvirus particle are
Answer: D
Correct answer: 240 nm by 300 nm
Poxviruses are the largest viruses of medical importance, big enough to be seen as brick-shaped bodies under the light microscope - which is how they were studied long before the electron microscope existed. At roughly 240 by 300 nm they are an order of magnitude larger in each dimension than a picornavirus, and their volume is correspondingly thousands of times greater, which is what allows them to carry a genome of several hundred kilobases.
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Parapoxvirus particles differ from other poxviruses in being
Answer: A
Parapoxviruses are narrower than the typical brick shape, at around 160 nanometres, and have a distinctive morphology that identifies them under the electron microscope. They also carry the smallest genome in the family, about 130 kilobases.
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Internally, a poxvirus virion contains
Answer: B
The core holds the genome and takes a dumbbell shape, with two lateral bodies filling the concavities on either side. This internal organisation is one reason the family is classed as having complex rather than helical or icosahedral symmetry.
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Virions released naturally from a poxvirus-infected cell differ from those extracted artificially in having
Answer: C
Naturally released particles carry an extra outer membrane that is absent from virions freed by breaking cells open in the laboratory. Both forms are infective, but they differ in their surface and therefore in how they are neutralised.
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Poxvirus replication takes place in
Answer: D
Correct answer: cytoplasmic inclusions
Almost every other DNA virus replicates in the nucleus, because that is where the host’s DNA polymerase and transcription machinery are. Poxviruses are the exception: they carry their own polymerases and transcription enzymes inside the particle, so they can build a self-contained factory in the cytoplasm. These factories are visible by light microscopy as inclusion bodies, the Guarnieri bodies once used to diagnose smallpox.
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Poxvirus DNA on its own is
Answer: A
Naked poxvirus DNA cannot start an infection, because the enzymes carried in the virion are required before the genome can be transcribed. That is the practical consequence of replicating in the cytoplasm rather than the nucleus.
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The enzymes a poxvirus needs to begin transcription are
Answer: B
Virion-associated enzymes are important for replication and travel inside the particle, since the cytoplasm offers none of the transcription machinery a nuclear virus would borrow. This is the same logic that makes the DNA alone non-infectious.
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