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Viruses and Bacteria

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  1. Viruses and Bacteria Chapter 18

  2. What is a virus? • Considered non-living particles by most biologists because they: • Do not carry out cellular respiration • Do not grow and develop • Cannot replicate on their own • Viruses are named after: • The disease they cause (poliovirus) • The organ they infect (adenovirus)

  3. Viral Structure • Genetic Material in the form of: • DNA • RNA • Capsid: outer protein coat • 4 common shapes • Polyhedral • Helical • Enveloped • Bacteriophage or phage

  4. Polyhedral Viruses • Herpes virus • Adenovirus • Polio virus

  5. Helical Viruses • Tobacco Mosaic Virus

  6. Enveloped Viruses • Contain an envelope made of • Lipids • Carbohydrates • Proteins • Examples • Influenza Virus • HIV

  7. Bacteriophages • “phage” • Is a virus that attacks bacteria

  8. Viruses are Specific • Each virus is specialized • Most viruses are species-specific • Many viruses are also cell-specific

  9. Viral Replication Cycles • Lytic Cycle • Kills the host cell • Lysogenic Cycle • Similar to lytic cycle but does not immediately kill host cell • Viral genetic material recombines with host cell’s DNA • Provirus: Viral DNA that is integrated into host cell’s chromosome • Examples: HSV I & II, hepatitis B, and chicken pox

  10. Lytic Cycle • A virus attaches to a host cell. • Virus releases its genetic material into the host cell. • The injected genetic material recruits the host cell's enzymes. • The enzymes make parts for more new viruses. • The new parts assemble into new viruses. • The new particles lyse (burst) the host cell and exit.

  11. Lysogenic Cycle

  12. Retroviruses • Type of RNA virus that reverse transcribes itself into DNA • The newly transcribed DNA inserts into host’s DNA • Ex: HIV

  13. Prokaryotes • Unicellular organisms without membrane-bound organelles • 2 Kingdoms • Archaebacteria • Eubacteria

  14. Archaebacteria • Live in harsh environments • 3 types • Methane-producers • “Methanogens” • Marshes • Lake sediments • Animal digestive tracts • Salt-dwellers • “Halophiles” • Dead Sea • Heat/Acid-dwellers • “Thermoacidophiles” • Deep ocean vents

  15. Eubacteria: The Heterotrophs • Bacteria that obtain their nutrients from elsewhere • Some are parasites • Feed off of living organisms • Some are saprophytes • Feed on dead organisms • Feed on organic wastes (recyclers)

  16. Eubacteria: Photosynthetic Autotrophs • Bacteria that convert solar energy into food • Cyanobacteria or blue-green algae • Found in aquatic environments • Composed of chains of independent cells

  17. Eubacteria: Chemosythetic Autotrophs • Break down and release energy from inorganic compounds such as H2S • Important in converting atmospheric nitrogen into usable forms plants need • Nitrogen Fixation

  18. Structure

  19. Identifying Bacteria: Gram Stain • Gram staining reflects differences in cell wall composition • Gram-positive bacteria stain blue/violet • Gram-negative bacteria stain pink

  20. Identifying Bacteria: Shapes

  21. Bacterial Reproduction • Asexually by binary fission • Very rapid at optimal conditions • can double every 20 minutes

  22. Bacterial Reproduction • Sexually by conjugation

  23. Common Bacterial Diseases

  24. Beneficial Bacteria • Nitrogen Fixation N2→ NO2- + NO3- Converts Nitrogen into a usable form for plants • Food • Yogurt • Cheese • Pickles • Sour cream • Sauerkraut