Antiviral agents act by
Answer: C
An antiviral interrupts one or more steps of the cycle inside the cell, which is a harder target than a bacterium because so much of the machinery being used belongs to the host. Supplying antibody is passive immunisation, a different approach entirely.
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Passive immunity against a virus is conferred by
Answer: D
Ready-made antibody is transferred rather than being raised by the recipient, so protection begins at once and fades as the antibody is cleared. Human immunoglobulin is used after a recent exposure, where no effective vaccine exists, or where illness prevents a vaccine response.
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Assembly of new virions takes place
Answer: A
The parts are made independently inside the cell and only then brought together, which is why the number of particles rises in a burst rather than by doubling. Maturation is the interval in which those assembled particles accumulate.
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An enveloped virus most characteristically leaves the host cell by
Answer: B
Budding wraps the nucleocapsid in host membrane already carrying viral glycoproteins, which is how the envelope is acquired. Because the cell need not be destroyed for release, budding is compatible with a persistent infection in a way that lysis is not.
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Why does a virus with a host-derived envelope not usually kill the cell at the moment of release?
Answer: C
A particle can take a patch of membrane and leave while the cell repairs itself, so release and cell death are separate events. A naked virus more often accumulates until the cell breaks, which is why the two groups differ in the kind of infection they tend to cause.
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Viral proteins that form part of the particle are described as
Answer: D
Structural proteins are those found in the finished virion, such as capsid subunits and envelope glycoproteins. Non-structural proteins, including polymerases and proteases, are made in the infected cell to run the cycle but are mostly not packaged.
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A polymerase carried inside a virion is best described as
Answer: A
Enzymes such as the RNA-dependent RNA polymerase of a minus-sense virus do no structural work, yet they must travel in the particle because the cell cannot supply them. That is why the structural and non-structural distinction describes function rather than location.
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A defective virus is one that
Answer: B
A defective particle lacks a function it needs, usually because part of the genome is missing, so it can only replicate where another virus supplies what is absent. It is still a virus, unlike a viroid or a prion, and it still has a genome.
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The virus that supplies the missing function to a defective virus is the
Answer: C
Correct answer: helper virus
A defective virus lacks a function it needs to complete its cycle, and the helper virus supplies that function when the two co-infect the same cell - hepatitis B acting as helper to hepatitis D is the classic medical example. The satellite virus is the dependent partner, not the provider, and a provirus is integrated viral DNA, which is a different idea entirely.
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An infection in which virus is produced continuously without killing the cell is described as
Answer: D
Correct answer: persistent
In a persistent infection the cell continues to release virus while remaining alive and dividing, so the culture is chronically infected rather than destroyed. That is what separates it from the lytic infection, which kills the cell to release the progeny, and from latency, in which the genome is retained but little or no virus is made.
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