Viruses V: Replicative Cycles of Animal Viruses

  1. a.      Like all viruses, those that cause illness in humans and other animals replicate only __host cells
    b.      Variations on basic scheme of viral infection and replication represented among __viruses
    • inside
    • animal
  2.                                                               i.      Nature of viral genome
    1.      Nature is basis for __ of viruses
    a.    __ further classified into three classes (IV-VI) according to how the __functions in host cell
    • common classification
    •   Single-stranded RNA viruses
    • RNA genome
  3.                                                               i.      Whereas few bacteriophages have an envelope or RNA genome, many animal viruses __
    1.      Nearly all animal viruses with RNA genomes have __, as well as __
    • have both
    • envelope
    • DNA genomes
  4. a.      Viral Envelopes
                                                                  i.      Animal virus equipped with envelope uses it to __

    1.      Protruding from outer surface of this envelope are __ that bind to specific __molecules on the surface of a host cell
    • enter host cell
    • viral glycoproteins
    • receptors
  5. 1.      __of host make the protein parts of envelope __; __ in ER and Golgi adds the __
    a.      Resulting viral glycoproteins, embedded in host cell-derived membrane, are sent to cell surface
    b.      Process like __-->new viral capsids are wrapped in membrane as they bud from cell
                                                                                                                                          i.      Viral envelope derived from host cell’s plasma membrane; some still specified by viral genes
    1.      Enveloped viruses now free to infect other cells
    2.      This cycle does not really kill cell
    • Ribosomes on ER
    • glycoproteins
    • cellular enzymes
    • sugars
    • exocytosis
  6.                                                               i.      Some viruses have envelopes not derived from plasma membrane
    1.      __: temporarily cloaked in membrane derived from __; shed it and get new envelope from __
    a.      These viruses have __and replicate within host __, using combo of viral and cellular enzymes to replicate and transcribe their DNA
    • Herpesviruses
    • host nuclear membrane;
    • Golgi membrane
    • double-stranded DNA genome
    • cell nucleus
  7. a.      Herpesvirus: copies of viral DNA remain as __ in nuclei of certain nerve cells and remain __until stress triggers new round of active virus production
                                                                                                                                          i.      Infection of other cells by these new viruses causes blisters
  8. mini-chromosomes
  9. a.      RNA as Viral Genetic Material
                                                                  i.      Broadest variety of RNA genomes found among viruses that infect __
    1.      Among three classes (IV-VI), __can directly serve as __and thus can be translated into __ immediately after infection
  10. animal
    • IV
    • mRNA
    • viral protein
  11. 1.      Class V (__ as template for mRNA synthesis)
    a.      RNA genome transcribed into complementary __, which function both as __and as __for the synthesis of additional copies of genomic RNA
    b.      All viruses that require RNAàRNA synthesis to make mRNA use viral enzyme capable of carrying out process
                                                                                                                                          i.      Viral enzyme packaged with genome inside __
    • RNA genome
    • RNA strands
    • mRNA
    • templates
    • viral capsid
  12. 1.      Class VI (__)
    a.      Equipped with enzyme called __, which transcribes an RNA template into DNA, providing an __ information flow, opposite the usual direction
    • retroviruses
    • reverse transcriptase
    • RNAà DNA
  13. a.      HIV causes AIDS
                                                                                                                                          i.      Enveloped viruses that contain two identical molecules of __and two molecules of __ 
    • single-stranded RNA
    • reverse transcriptase
  14. a.      HIV replicative cycle
                                                                                                                                          i.   ?
      Enters hostà reverse transcriptase released into cytoplasm, where they catalyze synthesis of viral DNAà new viral DNA enters cell’s nucleus and integrates into DNA of a chromosome (provirus)à permanent resident foreveràRNA polymerase transcribes proviral DNA into RNA molecules, which can function both as mRNA for the synthesis of viral proteins and as genomes for the new viruses that will be assembled and released from cell
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Viruses V: Replicative Cycles of Animal Viruses