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Viruses and Bacteria

This text discusses the characteristics of viruses and bacteria, their methods of infection, and control measures. It also covers viral diseases, vaccines, retroviruses, prions, bacterial classification, identification, growth and reproduction, and the importance of bacteria in the world.

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Viruses and Bacteria

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  1. Viruses and Bacteria

  2. Characteristics of viruses: • Viruses are particles of a nucleic acid and protein. • They can reproduce only by infecting living cells. Viruses are very specific: they can only attack one kind of cell.

  3. Methods of infection: • Lytic cycle-Virus enters a cell, makes copies of itself, and causes the cell to burst. a. Infection-DNA is injected into the cell, the capsid remains outside. The host usually cannot tell the difference between its own DNA and the viral DNA.

  4. b. Replication-the viruses uses material found in the cell to make copies of itself. c. Assembly- the cell puts the virus parts together.

  5. d. Lysis-the cell now contains as many as 500 viruses. It will now lyse or burst. Released viruses now infect other cells.

  6. The Lysogenic cycle-the virus does not become active right away. a. the DNA of the virus enters the cell and attaches to the host DNA. It is called a prophage.

  7. b. Mitosis occurs-normal cell division occurs where the virus DNA is copied along with the host cell DNA. c. Activation-something will trigger the virus to enter the lytic cycle.

  8. Viral diseases, vaccines, retroviruses and prions • Some viral disease include: polio, measles, AIDS, mumps, influenza, rabies, yellow fever, and the common cold.

  9. The best protection against viral disease is prevention which is best achieved with vaccines. They contain dead or weakened virus that will cause the immune system to create immunity against the disease. The immunity may be lifelong or temporary.

  10. Oncoviruses are viruses that cause cancer in animals by upsetting the normal growth and division of the cell.

  11. Retroviruses contain RNA instead of DNA. They must first make a copy of DNA inside the cell. An example of this is HIV.

  12. Prions are infectious proteins. They have no DNA or RNA. An example is mad cow disease.

  13. Bacteria Classification: 1. Kingdom Eubacteria-larger of the 2 kingdoms, can live almost anywhere. The cells are very small and do not have a nucleus.

  14. Bacterial cell diagram

  15. 2. Kingdom Archaebacteria-look much like eubacteria but biochemically they are different. Many live in harsh places like the great salt lake, some produce methane gas.

  16. Bacteria are the smallest cells known

  17. Identification 1. By cell shape rod-bacillus round-coccus spiral-spirillum

  18. 2. By growth patterns • chains--strep • pairs--diplo • clumps--staph • fours--tetra

  19. 3. By type of cell wall. The gram stain was developed by Christian Gram and uses 2 dyes: • gram positive-stains purple (crystal violet) • cell has one thick cell wall • gram negative-stains red (safranine) • cell has 2 thin cell walls

  20. 4. By movement • flagella-may have more than one • secretes slime that it slides over

  21. Growth and reproduction: • May divide every 20 minutes if conditions are ideal. In two days they would equal a mass 4000 times the earth. • what are ideal conditions for bacteria?

  22. Binary fission-cell copies its DNA and divides into two cells. There is no exchange of genetic material. All cells are identical.

  23. Conjugation • some bacteria exchange DNA before they divide by building a bridge between them. • This insures diversity

  24. Spore formation • When growth conditions are poor the bacteria can be dormant for years. • One type is an endospore which encloses the DNA inside the cell.

  25. The importance of bacteria in the world: • Production of food such as yogurt, cheeses, pickles • Cleaning up oil in oil spills

  26. Making drugs and medicines • Help digest food in intestines • Decomposers-help to recycle organic matter

  27. Nitrogen fixers-take nitrogen from air and put it into soil

  28. Many are pathogens and cause diseases either by tissue damage or making toxins. Lyme disease

  29. Cover your mouth!Wash your hands!

  30. Control of bacteria 1. Sterilization-using heat or chemicals 2. Canning-sealing without oxygen

  31. 3. Chemicals-salt, sugar, preservatives 4. Refrigeration or freezing- slows growth but won’t kill all bacteria

  32. 5. Drying-removes moisture needed for growth

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