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  1. Sub-microscopic (20 -50 nanometres) obligate intracellular parasites
  2. Their genetic element is either RNA or DNA (not both) that is wrapped into a protein coat (capsid)  and some with lipid envelope enclosing the coat
  3. Viruses survive and replicate only in living susceptible cells

 

 

“A piece of bad news wrapped up in a protein”