Think questions
- What is a virion? What is the difference between a virus and a virion?
- Why are viruses considered obligate intracellular pathogens?
- Describe three reasons why it is important to study viruses
- 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.
- Why is it likely that viruses have not evolved from free-living organisms?
- What characteristics of viruses made it difficult for viruses to discover them?
- How were Chamberland filters useful in the discovery of viruses?
- Give examples of infectious agents that are smaller self-replicating systems than viruses.
- 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?
- 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?
- Recount the scientific investigations that led to the discovery of viruses. Include the contributions of Adolf Mayer, Dimitri Ivanowsky, Martinus Beijerinck, and Wendell Stanley
- Explain why viruses are obligate intracellular parasites
- List some characteristics that viruses share with living organisms and explain why viruses do not fit our usual definition of life
- Describe the evidence that viruses probably evolved from fragments of cellular nucleic acids
- What is a viroid? How does it differ from a virus?
- 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?
- Outline one apparent mechanism of replication for viroids. Where in the host cell does this take place?
- Compare and contrast viroids, virusoids, satellite viruses, satellite RNA, pseudovirions, and DI particles. (A table is a good approach.)
- Why is viroid RNA amazingly stable?
- List three differences between hepatitis delta-agent and other viroids.
- Define prions. How do they differ from true “slow viruses”?
- What evidence is there that supports nucleic acid coding for prions?
- What evidence is there that supports something other than nucleic acids for the “coding” of prions?
- With regard to chemical agents and processing protocols, compare the sensitivities and resistances of prions to true viruses
- “Computer virus” is coined as an analogy to “virus.” State in what respects these two seemingly unrelated entities are related.
- List three kinds of subviral agents and state why each of these subviral agents does not comply with the classical definition of a “virus.”