Poliovirus belongs to the family
Answer: A
The picornaviruses are small naked icosahedral viruses with positive-sense single-stranded RNA, and the family also contains the rhinoviruses and hepatitis A virus. Their name records both their size and their genome: pico for small and rna for the nucleic acid.
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Rabies virus belongs to the family
Answer: B
Rhabdoviruses are enveloped, bullet-shaped and carry negative-sense single-stranded RNA, so each virion must bring its own polymerase. The characteristic shape and the neuronal inclusions it produces make rabies one of the most recognisable virus infections.
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Human immunodeficiency virus belongs to the family
Answer: C
Retroviruses carry positive-sense single-stranded RNA together with reverse transcriptase, which copies the genome into DNA for integration into the host chromosome. That integration is why infection is permanent and why treatment must be lifelong.
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Smallpox virus belongs to the family
Answer: D
Poxviruses are the largest and most complex animal viruses, carrying double-stranded DNA and replicating entirely in the cytoplasm with enzymes of their own. Their size is such that the virion approaches the limit of what a light microscope can detect.
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Hepatitis B virus is unusual among DNA viruses because it
Answer: A
The hepadnaviruses carry DNA but copy an RNA intermediate back into DNA with a reverse transcriptase, a strategy otherwise associated with retroviruses. That shared enzyme is why some drugs are active against both hepatitis B virus and the human immunodeficiency virus.
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Measles virus and mumps virus both belong to the
Answer: B
Paramyxoviruses are enveloped, with a flexible helical nucleocapsid and negative-sense single-stranded RNA that is not segmented. Their fusion glycoprotein is what produces the multinucleate giant cells seen in measles.
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Which one of the following viruses is naked, that is without an envelope?
Answer: C
Adenoviruses are naked icosahedral particles, which is part of why they survive well on surfaces and spread readily. The other three are all enveloped, and each is correspondingly more vulnerable to drying and to lipid solvents.
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Which one of the following viruses is enveloped?
Answer: D
Influenza virions acquire a lipid envelope by budding, and the haemagglutinin and neuraminidase spikes sit in it. The others are naked, and the difference explains why influenza is inactivated by soap and alcohol far more readily than poliovirus.
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Bacteriophages differ from the viruses of this topic chiefly in that they infect
Answer: A
A phage is simply a virus whose host is a bacterium, so the entry problem is different: it must cross a cell wall rather than a plasma membrane, and many inject their genome while the coat stays outside. Eukaryotic viruses instead enter whole and uncoat inside.
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An arbovirus is defined by
Answer: B
Correct answer: transmission by an arthropod vector
Arbovirus is short for arthropod-borne virus, and the term is ecological rather than taxonomic: it groups viruses transmitted by mosquitoes, ticks and sandflies regardless of family. Dengue, yellow fever, chikungunya and tick-borne encephalitis belong to three different families and are all arboviruses, because what they share is a life cycle requiring replication in the vector as well as the host.
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