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  1. 1. Viruses Chapter 18
  2. 2. What is a virus? •Microscopic particle (microbe) that invades the cells of living organisms.
  3. 3. Basic Structure Virus • “Particles” • Core- nucleic acid (DNA or RNA) • Capsid- protein coat surrounds core
  4. 4. Are viruses living things? Are viruses living things? Characteristic Cells Characteristic Metabolism Yes/No Comments Yes/No Comments No particles – can not make proteins No too simple to obtain/make energy; only need it to reproduce - steal it from cells infect Reproduce Yes Only inside host cell Heredity Yes DNA or RNA Homeostasis No No method for controlling internal environment Reproduce Cells Heredity Metabolism Homeostasis
  5. 5. Why should we study viruses?
  6. 6. In order to replicate, In order to exist and a virus reproduce, must invade a a virus must invade living cell. a living cell. This living This living cell is referred to cell is referred to as a host. a host. as
  7. 7. Viral Replication General Steps: • Recognition • Attachment • Injection • Assembly • Lysis
  8. 8. How do viruses infect your cells? Lytic Virus •Examples: Common Cold Flu •Replicates immediately and kills the host cell •You get sick right away.
  9. 9. How do viruses infect your cells? Lysogenic Virus •Examples: VIRAL DNA HIV Shingles •Does not kill host cell immediately •Viral DNA injected into host cell and then fuses with host cell DNA •Dormant period •You don’t get sick right away
  10. 10. Protection Against Viruses • All viruses are pathogens. • Animals, plants, fungi, protists, and bacteria can all be infected by viruses. • Antibiotics do not work. • Antiviral medications • Vaccines are used as prevention only. • Vaccinations are ONLY useful against viruses that do NOT evolve rapidly. • Flu shot- many different types- flu