A complete, fully assembled virus particle is called
Answer: A
The virion is the complete particle, the form in which a virus exists outside a cell and the vehicle that delivers the genome to the next host cell. A capsomere is only a cluster of subunits within the shell, and a peplomer is a glycoprotein spike on an envelope.
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The protein shell that encloses a viral genome is the
Answer: B
The capsid is built from many copies of one or a few proteins that self-assemble into a symmetric shell, protecting the nucleic acid and taking part in attachment. The envelope, where present, lies outside the capsid and is membrane rather than protein.
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Clusters of protein subunits visible on a capsid under the electron microscope are termed
Answer: C
Capsomeres are the oligomeric groupings of structural polypeptides that make up an icosahedral shell and are the repeating units seen in electron micrographs. Counting them was one of the earliest ways of assigning a virus to a family.
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The viral genome together with its closely associated nucleoprotein forms the
Answer: D
Nucleoprotein bound along the nucleic acid, plus that nucleic acid, is the nucleocapsid. In an enveloped virus the nucleocapsid is the structure that the membrane is acquired around, which is why the two terms are not interchangeable with capsid.
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The lipid of a viral envelope is derived from
Answer: A
An enveloped virus buds through the plasma membrane or another cell membrane and takes lipid with it, so the envelope's lipid composition closely reflects the particular host membrane it left through. The virus supplies only the glycoproteins inserted into that lipid.
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Glycoprotein spikes projecting from a viral envelope are called
Answer: B
Correct answer: peplomers
Peplomers are the glycoprotein spikes embedded in the lipid envelope, and they carry the functions that meet the host - attachment to the receptor, fusion of the membranes, and in influenza the neuraminidase that releases new particles. Because they are exposed they are also the principal antigens, which is why antigenic change in them defeats immunity. Capsomeres are the protein subunits of the capsid, and fimbriae and pili are bacterial appendages.
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Which one of the following capsid symmetries is found in tobacco mosaic virus?
Answer: C
In helical symmetry the protein subunits form a helix around the nucleic acid, producing a rod or a filament; tobacco mosaic virus is the classic rigid rod. Flexible helical nucleocapsids occur in paramyxoviruses such as Sendai virus.
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An icosahedron has
Answer: D
An icosahedron is a polyhedron of 20 equilateral triangular faces with 12 vertices, and it shows 5-3-2 rotational symmetry. It is the shape that encloses the largest volume for a given number of identical subunits, which is why so many viruses adopt it.
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Adenoviruses and polioviruses both show
Answer: A
Both build closed icosahedral shells, as does hepatitis A virus. Helical symmetry is the alternative basic plan, seen in tobacco mosaic virus and the rhabdoviruses, while poxviruses are the standard example of a complex architecture belonging to neither class.
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The approximate size range of virions is
Answer: B
The smallest virions, such as the circoviruses, are about 17 nm across, while some helical nucleocapsids reach about 1,000 nm. Even the largest is well below the resolution of a light microscope, which is why electron microscopy was needed to see them.
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