An introduction to the viruses

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An introduction to the viruses

  1. 1. PowerPoint to accompanyFoundations in Microbiology Fifth Edition Talaro Chapter 6 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  2. 2. An Introduction to the Viruses Chapter 6 2
  3. 3. 3
  4. 4. Size of viruses 4
  5. 5. Naming viruses• No taxa above Family (no kingdom, phylum, etc)• 19 families of animal viruses• Family name ends in -viridae , Herpesviridae• Genus name ends in -virus, Simplexvirus• Herpes simplex virus I (HSV-I)
  6. 6. • Family – Herpesviridae• Genus – Varicellovirus• Common name – chickenpox virus• Disease - chickenpox 6
  7. 7. capsids• All viruses have capsids- protein coats that enclose & protect their nucleic acid• Each capsid is constructed from identical subunits called capsomers made of protein• 2 types: – helical – iscosahedral 7
  8. 8. helical 8
  9. 9. icosahedral 9
  10. 10. icosahedral • 20-sided with 12 corners • Vary in the number of capsomers • Each capsomer may be made of 1 or several proteins • Some are enveloped 10
  11. 11. complex Fig 6.9a,c
  12. 12. 6 steps in phage replications adsorption – binding of virus to specific molecule on host cells penetration –genome enters host cells replication – viral components produceds assembly - viral components assembleds maturation – completion of viral formations release – viruses leave cell to infect other cells
  13. 13. Fig 6.11 13
  14. 14. penetration 14
  15. 15. Bacteriophage assembly line 15
  16. 16. • Not all bacteriophages lyse cells• Temperate phages insert their viral DNA into the host chromosome & viral replication stops at there until some later time.• Lysogeny- bacterial chromosome carries phage DNA 16
  17. 17. Host range• Spectrum of cells a virus can infect – cell has to have a specific structure (receptor) on its surface for viral attachment – cell has to contain all of the enzymes and materials needed to produce new virions• May be one species or many – HIV (only humans) vs rabies (many animals)• May be one tissue or many within a host – Hepatitis (liver) vs polio (intestinal & nerve cells) 17
  18. 18. Differences between phage and animal virus replication2. Animal virus replication is more complex than phage replication because host cells are more complex.3. Animal viruses cannot inject their DNA.4. Lysogeny for phage, latency for animal viruses 18
  19. 19. Animal virus replication1. adsorption2. penetration/uncoating of genome3. duplication/synthesis4. assembly5. release 19
  20. 20. 20
  21. 21. adsorption 21
  22. 22. penetration 22
  23. 23. Release by budding 23
  24. 24. Cytopathic effects- virus-induced damage to cells1. changes in size & shape2. cytoplasmic inclusion bodies3. nuclear inclusion bodies4. cells fuse to form multinucleated cells5. cell lysis6. alter DNA7. transform cells into cancerous cells 24
  25. 25. Cytopathic changes in cells 25
  26. 26. How do we grow viruses? Obligate intracellular parasitesrequire appropriate cells to replicate.
  27. 27. Growing animal viruses1. live animals2. bird embryos – chicken, duck; intact, self- supporting unit, sterile, self-nourished3. cell culture 27
  28. 28. 28
  29. 29. 29
  30. 30. Other noncellular infectious agents• prions - misfolded proteins, contain no nucleic acid – cause spongiform encephalopathies – holes in the brain – common in animals • scrapie in sheep & goats • bovine spongiform encephalopathies (BSE), aka mad cow disease • humans – Creutzfeldt-Jakob Disease• viroids - short pieces of RNA, no protein coat – only been identified in plants, so far 30
  31. 31. Diagnosis of viral diseases• More difficult than other agents• Consider overall clinical picture• Take appropriate sample – Infect cell culture- look for characteristic cytopathic effects – Screen for parts of the virus – Screen for immune response to virus (antibodies) 31
  32. 32. diagnosis 32

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