Specific binding of a virion protein to a molecule on the cell surface is
Answer: D
Attachment is a specific recognition event between a viral anti-receptor and a host cell constituent, which is why a virus infects only cells carrying the right molecule. Penetration is the entry that follows, and uncoating the release of the genome after that.
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Penetration of a virus into a host cell is described as
Answer: A
Penetration requires energy and proceeds by translocation across the membrane, by endocytosis, or by fusion of a viral envelope with a cell membrane. Attachment by contrast can occur on a cell that is metabolically inactive, because it is only binding.
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During uncoating,
Answer: B
Uncoating is the disaggregation of the particle, alone or with help from cellular enzymes, which sets the stage for the genome to be read. Assembly and envelopment happen much later, and egress is the final step of the cycle.
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The interval shortly after infection when only small amounts of parental infectious virus can be detected is the
Answer: C
During the eclipse the genome has been uncoated and exposed to the machinery that will express it, so no intact infectious particle exists to be recovered. Detectable virus reappears once maturation begins and progeny accumulate.
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The phase in which progeny virions accumulate at exponential rates is
Answer: D
Maturation is the interval in which finished particles build up inside the cell or outside it, following the eclipse during which none could be detected. The rise is exponential because many genomes and coat proteins are being assembled at once.
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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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