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Virus

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  1. Virus

  2. Warm-up • What is a pathogen? • What is a virus? • What is a viroid? • What is a prion?

  3. Virus Virus • Infectious particle made only of DNA or RNA and surrounded by a protein coat • virus comes from Latin “poison” • living? or non-living? rabies virus

  4. Virus Viroid • Infectious particles that cause disease in plants • Single stranded RNA that does not have a protein coat • Passed through seeds or pollen • Stunt growth of plant

  5. Virus Prion • Infectious particle made only of protein • Causes other proteins to fold incorrectly • Infectious but have no genetic material • No immune response • Example: Mad Cow Disease

  6. Virus Virus First virus • Wendell Stanley (1935) • studying splotchy leaves on tobacco • discovered and isolated tobacco mosaic virus (TMV)

  7. Virus Structure of a Virus • nucleic acid core (DNA or RNA), surrounded by outer protein coat called a capsid • different shapes: hellical (rod), sperical, polyhedral, different sizes 17nm – 100nm • some have an envelope with spikes that surrounds the capsid • contain no cell organelles, carry out no metabolic reactions • reproduce only inside a host cell • many are host specific • classified by type of nucleic acid and shape

  8. Virus Structure of a Virus • nucleic acid core (DNA or RNA), surrounded by outer protein coat called a capsid

  9. Virus Structure of a Virus • different shapes: hellical (rod), sperical, polyhedral, different sizes 17nm – 100nm

  10. Virus Structure of a Virus • some have an envelope with spikes that surrounds the capsid HIV

  11. Virus Structure of a Virus • many are host specific • ex: bacteriophage only infects bacteria

  12. Virus Structure of a Virus • contain. . . no cell organelles, • carry out. . . no metabolic reactions • reproduce. . . only inside a host cell

  13. Virus Structure of a Virus • classified by type of nucleic acid and shape

  14. Structure of a Virusclassified by type of nucleic acid and shape

  15. Virus Viral Reproduction Lytic Cycle (DNA virus) • virus takes over host cell, replicates, and destroys host cell • Steps • attachment • entry • replication • formation & assembly • lysis & release

  16. Virus Viral Reproduction Lytic Cycle (DNA virus) • viruses use nucleotides, ribosomes, tRNA, and amino acids of host cell • viruses that undergo the lytic cycle are called virulent – short incubation time rhino virus

  17. Virus Viral Reproduction Lytic Cycle (DNA virus)

  18. Virus Viral Reproduction RNA virus Lytic cycle Steps • (almost the same as DNA virus) • attachment • entry • replication • replication of viral RNA • formation & assembly • lysis & release

  19. Virus Viral Reproduction Lysogenic Cycle (DNA virus) • virus invades cell and becomes part of its DNA for a time • Steps • attachment • entry • intergration • viral DNA breaks open host cell DNA and joins with it forming a provirus • cell division • host cell divides, produces 2 new host cells with the provirus inside

  20. Virus Viral Reproduction Lysogenic Cycle (DNA virus) • provirus may: • change phenotype of host • prevent other viruses from entering host • pull out of host DNA & enter lytic cycle

  21. Virus Viral Reproduction Lysogenic Cycle (DNA virus) • viruses that go through lysogenic cycle are temperate viruses – long incubation period herpes simplex

  22. Virus Viral Reproduction Lysogenic Cycle (DNA virus)

  23. Virus Viral Reproduction Lysogenic Cycle (DNA virus)

  24. Virus Viral Reproduction RNA virus Lysogenic cycle Steps • inject viral RNA into host • viral RNA makes a DNA copy using reverse transcriptase • DNA strand replicates and enters host DNA to become a provirus

  25. Virus Viral Reproduction RNA virus Lysogenic cycle • RNA viruses that go through the lysogenic cycle are called retroviruses HIV

  26. Virus Treating Viruses vaccine • injection of weakened or killed viruses Jonas Salk (1955) • developed first vaccine for the polio virus

  27. Virus Other Viruses polio

  28. Virus Other Viruses measles

  29. Virus Other Viruses smallpox