An infection in which the viral genome is present but no infectious particles are produced is
Answer: A
During latency the genome is maintained in the cell without new virions being made, so the infection is invisible to methods that look for particles. Reactivation restores production, which is why serology and nucleic acid detection matter for such agents.
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An abortive infection is one in which
Answer: B
Correct answer: the virus enters but the cycle is not completed
In an abortive infection attachment and entry succeed but some later step fails, so no infectious progeny are produced. The cause may lie with the cell - a non-permissive cell lacking a factor the virus needs - or with the virus, if the particle is defective. The cell may nonetheless be damaged or transformed, so an abortive infection is not necessarily a harmless one.
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Antibacterial antibiotics are ineffective against viruses because viruses
Answer: C
Antibiotics work by attacking structures and processes peculiar to bacterial cells, and a virus has none of them, using the host's machinery instead. That is also why antiviral drugs are harder to design without harming the host.
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Viruses are generally too small to be seen with
Answer: D
Most virions are smaller than the resolving limit of visible light, so the electron microscope is the instrument that shows them. Their effects on cells, such as inclusions, can be seen by light microscopy even when the particles cannot.
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Inclusions seen in an infected cell under the light microscope are useful because they
Answer: A
Correct answer: indicate viral growth without resolving particles
A virion is far below the resolving power of a light microscope, but the aggregates of viral protein and nucleic acid that accumulate at sites of replication are large enough to be seen and stained. The inclusion is therefore evidence of infection rather than a view of the virus, and its position and staining can be characteristic - Negri bodies in rabies being the classic example.
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The nucleic acid of a virus may be
Answer: B
Correct answer: single or double stranded, and linear or circular
Viruses use every arrangement of nucleic acid found in nature and some found nowhere else: DNA or RNA, single or double stranded, linear, circular or segmented, and in the case of single-stranded RNA either positive or negative sense. No other group of infectious agents shows this variety, and it is one of the reasons virus classification rests on genome type.
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In a helical virus, the length of the nucleocapsid is set by
Answer: C
Protomers add along the genome, so a longer genome gives a longer particle while the diameter stays fixed. An icosahedral capsid behaves the other way: it is a closed container of set size, which limits how much nucleic acid will fit.
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Building a capsid from many copies of one protein is advantageous because it
Answer: D
Encoding one subunit and repeating it costs far less genetic information than encoding a large unique shell, which matters when the genome is small. The symmetry of the icosahedron is what makes such repetition geometrically possible.
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The matrix protein of an enveloped virus lies
Answer: A
Correct answer: between the nucleocapsid and the envelope
The matrix protein forms a layer lining the inner face of the envelope and contacting the nucleocapsid, so it links the two. That position is what makes it structurally important: it gives the envelope its rigidity and it directs assembly, gathering the nucleocapsid beneath the patch of membrane carrying the viral glycoproteins so that budding produces a complete particle.
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Naked viruses are typically well suited to transmission by
Answer: B
A protein capsid survives stomach acid, bile and drying far better than a lipid envelope, so naked viruses persist in the environment and on surfaces. Enveloped viruses more often need close or moist contact because their lipid is fragile.
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