Papovavirus, adenovirus and herpesvirus genomes are transcribed and replicated in the
Answer: A
These DNA viruses use the host's nuclear machinery for transcription and replication, which is the usual arrangement for DNA viruses. The pattern is not universal, and poxviruses are the standard exception that proves the rule.
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Which DNA virus group carries out transcription and most of its reproductive cycle in the cytoplasm?
Answer: B
Poxviruses are the exception among DNA viruses: transcription and most other events of the cycle take place in the cytoplasm, which means the virus must encode its own transcription machinery rather than borrowing the nucleus. The other three groups all use the nucleus.
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In orthomyxovirus entry, the particle is taken into an endocytic vesicle and uncoating is helped by
Answer: C
A channel embedded in the envelope lets protons in and the resulting acidification loosens the particle so the genome can be released. It is a good illustration that uncoating is not one mechanism but several, differing by family.
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Uncoating in which of these groups removes only portions of the capsid?
Answer: D
Reovirus particles are only partly stripped, and transcription then proceeds inside the remaining core rather than from free nucleic acid. Poxviruses are uncoated in two distinct stages, which is another departure from the simple picture of a capsid falling away entirely.
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Viroids consist of
Answer: A
A viroid is a small, very stable circular RNA of roughly three to four hundred bases, carrying no capsid at all. They are plant pathogens, and the absence of a coat is the clearest difference from a conventional virus.
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A prion is best described as
Answer: B
The term means a proteinaceous infectious agent, and the defining claim is that no nucleic acid can be demonstrated in it. That sets it apart from viroids, which are RNA without protein, and from viruses, which always carry a genome.
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Which pair correctly contrasts a viroid with a prion?
Answer: C
The two are near mirror images. A viroid is a naked circular RNA with no coat, while a prion is proteinaceous with no demonstrable nucleic acid, so they represent fundamentally different infectious mechanisms and neither is a virus.
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The range of cells a particular virus can infect is determined largely by
Answer: D
Attachment is a specific binding event, so a cell without the matching surface constituent cannot be entered however permissive its interior might be. This is why tropism is often described first in terms of receptors, and why receptor distribution predicts which tissues a virus damages.
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The viral surface protein that binds the host cell receptor is called the
Answer: A
The virion protein that recognises the cell is the anti-receptor, and the cell surface molecule it binds is the receptor. The matrix protein lies beneath an envelope and the core protein packages the genome, so neither is exposed for binding.
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Which feature is present in bacteria but absent from viruses?
Answer: B
Bacteria are cells and carry ribosomes, so they synthesise their own proteins and generate their own energy. A virus has nucleic acid and protein but no ribosomes, which is precisely why it must borrow a cell's machinery to replicate.
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