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Think questions

  1. What is a virion? What is the difference between a virus and a virion?
  2. Why are viruses considered obligate intracellular pathogens?
  3. Describe three reasons why it is important to study viruses
  4. Viruses are a part of the biosphere. However, there is active debate concerning whether they should be treated as living or non-living.   a) Briefly describe one feature of viruses that are also found in cell-based life forms.                                                                                               b) Briefly describe one feature of viruses that distinguishes them from cell-based life forms.
  5. Why is it likely that viruses have not evolved from free-living organisms?
  6. What characteristics of viruses made it difficult for viruses to discover them?
  7. How were Chamberland filters useful in the discovery of viruses?
  8. Give examples of infectious agents that are smaller self-replicating systems than viruses.
  9. Ebola virus is a deadly (90% case-fatality rate for some strains) infectious agent. Most viruses, however, are not nearly as lethal. Given the nature of viruses, why would you expect this to be so?
  10. Given that viruses are a part of the biosphere in which other organisms exist, what might be the kinds of selective pressure that viruses exert on evolution?
  11. Recount the scientific investigations that led to the discovery of viruses. Include the contributions of Adolf Mayer, Dimitri Ivanowsky, Martinus Beijerinck, and Wendell Stanley
  12. Explain why viruses are obligate intracellular parasites
  13. List some characteristics that viruses share with living organisms and explain why viruses do not fit our usual definition of life
  14. Describe the evidence that viruses probably evolved from fragments of cellular nucleic acids
  15. What is a viroid? How does it differ from a virus?
  16. It is hypothesized that many of the viroids either co-descended with introns from some precursor or are descended from introns. What evidence is there to support this hypothesis?
  17. Outline one apparent mechanism of replication for viroids. Where in the host cell does this take place?
  18. Compare and contrast viroids, virusoids, satellite viruses, satellite RNA, pseudovirions, and DI particles. (A table is a good approach.)
  19. Why is viroid RNA amazingly stable?
  20. List three differences between hepatitis delta-agent and other viroids.
  21. Define prions. How do they differ from true “slow viruses”?
  22. What evidence is there that supports nucleic acid coding for prions?
  23. What evidence is there that supports something other than nucleic acids for the “coding” of prions?
  24. With regard to chemical agents and processing protocols, compare the sensitivities and resistances of prions to true viruses
  25. “Computer virus” is coined as an analogy to “virus.” State in what respects these two seemingly unrelated entities are related.
  26. List three kinds of subviral agents and state why each of these subviral agents does not comply with the classical definition of a “virus.”