Читать книгу Principles of Virology - Jane Flint, S. Jane Flint - Страница 216

1 Icosahedral virus particles are NOT stabilized by:Specific “cement” or “glue” proteinsCovalent bondsInteractions between adjacent protein layersTransmembrane connections of envelope to capsid proteinsNone of the above

2 Both picornaviruses (e.g., poliovirus) and polyomaviruses (e.g., simian virus 40) comprise small genomes packaged within icosahedral capsids.Indicate one similarity and two differences in the structures of poliovirus and simian virus 40 capsidsExplain how ONE of these capsids does not conform to the rules of quasiequivalence

3 Which of the following statements describes interactions among components of virus particles?Subunits usually associate via covalent bondsEach subunit has different bonding contacts with its neighborsCapsid subunits cannot interact with the internal viral genomeSubunits usually associate noncovalentlySubunit-subunit interactions are always sufficient to stabilize virus particles

4 It has long been known that virus particles can contain host cell molecules.Why is it difficult to be sure that host cell molecules found in enveloped virus particles are packaged specifically?If specific incorporation of a cellular protein into particles of a virus had been demonstrated, how would you investigate the functional importance of capture of the cellular protein?

5 Viral envelopes:Are invariably derived from host cell membranesContain viral glycoproteins with external and internal domains connected by transmembrane segmentsCan lie above or underneath a capsidAre generally impermeable to ions and charged moleculesAll of the above

6 What are the three modes of packing viral genomes in virus particles? Give an example of each mode of packaging.

7 Characteristic features of large virus particles do NOT include:Distinct parts with helical or icosahedral symmetryThe presence of multiple viral enzymesStructures dedicated to exit of the viral genomeMore than a single membraneA large DNA or RNA genome

8 Mature virus particles are said to be metastable.Explain what is meant by this term and why virus particles must be metastablePredict the consequences of a mutation that precludes formation of metastable virus particles during assembly and maturation

9 Which of the following statements about helical symmetry is INCORRECT?Helical viruses can contain RNA or DNA genomesThese genomes can be packaged by either specialized nucleic acid binding proteins or direct contact with coat proteinsAs the structure of a helix is open, the largest known viruses display helical symmetryHelical viruses can be naked or envelopedViral enzymes are present in many helical viruses that reproduce in animal cells

10 You have recently isolated a virus associated with a human disease. The virus particles are spherical, ~100 nm in diameter, and possess an envelope. Preliminary genome sequence analysis suggests the virus is not related to known human viruses.Indicate how you would determine the structure of this virus, and the rationale for your choice of methodWhich protein topology would you be most likely to find in the major capsid protein?

11 Subunits of viral capsid proteins are ~20 to 100 kDa.Explain how large icosahedral capsids can be assembled and how they differ from small capsidsWhat feature(s), other than genetic economy, dictates that all capsids are built from only a very small number of major structural proteins?