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33. an introduction to the viruses

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33. an introduction to the viruses

  1. 1. An Introduction to the Viruses Topic 36 and Topic 37
  2. 3. Size of viruses
  3. 5. The Viral Structures and Shape
  4. 6. Capsids <ul><li>All viruses have capsids- protein coats that enclose & protect their nucleic acid </li></ul><ul><li>Each capsid is constructed from identical subunits called capsomers made of protein </li></ul><ul><li>2 types: </li></ul><ul><ul><li>helical </li></ul></ul><ul><ul><li>iscosahedral </li></ul></ul>
  5. 7. Shape of Viruses, determined by the arrangement of proteins (capsomers) in the capsid
  6. 8. Helical
  7. 9. Icosahedral
  8. 10. Icosahedral <ul><li>20-sided with 12 corners </li></ul><ul><li>Vary in the number of capsomers </li></ul><ul><li>Each capsomer may be made of 1 or several proteins </li></ul><ul><li>Some are enveloped </li></ul>
  9. 11. Additional Structures in some Viruses, envelope and surface proteins
  10. 12. Function of the envelope
  11. 13. Complex Viruses-1 <ul><li>Two special groups of viruses termed Complex viruses. </li></ul><ul><ul><ul><li>More intricate in structure than the helical, icosahedral, naked or enveloped </li></ul></ul></ul><ul><li>These are : </li></ul><ul><ul><li>Poxviruses : very large viruses that contain a DNA core </li></ul></ul><ul><ul><li>but lack a regular capsid, in its place are </li></ul></ul><ul><ul><li>several layers of lipoprotein and coarse </li></ul></ul><ul><ul><li>surface fibrils </li></ul></ul>
  12. 14. Complex Viruses-2 <ul><li>Bacteriophage : another complex virus </li></ul>Polyhedral head Helical tail Fibers for attachment to host cell
  13. 15. Naming viruses <ul><li>No taxa above Family (no kingdom, phylum, etc) </li></ul><ul><li>19 families of animal viruses </li></ul><ul><li>Family name ends in -viridae , Herpesviridae </li></ul><ul><li>Genus name ends in -virus, Simplexvirus </li></ul><ul><li>Herpes simplex virus I (HSV-I) </li></ul>
  14. 16. <ul><li>Family – Herpesviridae </li></ul><ul><li>Genus – Varicellovirus </li></ul><ul><li>Common name – chickenpox virus </li></ul><ul><li>Disease - chickenpox </li></ul>EXAMPLE of VIRAL TAXONOMY
  15. 17. Virus taxonomy based on viral characteristics <ul><li>In contrast to other discipline where taxonomy is well defined, viral taxonomy is much less structured and depends on a variety of characteristics including : </li></ul><ul><ul><ul><li>Nucleic acid type : DNA or RNA </li></ul></ul></ul><ul><ul><ul><li>Nucleic acid strandedness: single stranded (ss) or double stranded ( ds) </li></ul></ul></ul><ul><ul><ul><li>Presence or absence of an envelope </li></ul></ul></ul><ul><ul><ul><li>Capsid size or shape : icosahedral or helical </li></ul></ul></ul><ul><ul><ul><li>Host specificity, e.g. plant, animal, bacteria </li></ul></ul></ul>
  16. 18. Example of the Taxonomic characteristics , used to describe a virus
  17. 19. VIRAL REPLICATION
  18. 20. Phage Replication
  19. 21. 6 steps in phage replication <ul><li>adsorption – binding of virus to specific molecule on host cell </li></ul><ul><li>penetration –genome enters host cell </li></ul><ul><li>replication – viral components produced </li></ul><ul><li>assembly - viral components assembled </li></ul><ul><li>maturation – completion of viral formation </li></ul><ul><li>release – viruses leave cell to infect other cells </li></ul>
  20. 22. Fig 6.11
  21. 23. Penetration
  22. 24. Bacteriophage assembly line
  23. 25. <ul><li>Not all bacteriophages lyse cells </li></ul><ul><li>Temperate phages insert their viral DNA into the host chromosome & viral replication stops at there until some later time. </li></ul><ul><li>Lysogeny - bacterial chromosome carries phage DNA </li></ul>Impact of Bacteriophages
  24. 26. Animal Virus Replication
  25. 27. Stages of Animal virus replication <ul><li>adsorption </li></ul><ul><li>penetration/ </li></ul><ul><li>uncoating of genome </li></ul><ul><li>3. duplication/synthesis </li></ul><ul><li>4. assembly </li></ul><ul><li>5. release </li></ul>
  26. 28. Virus Adsorption
  27. 29. Virus Adsorption <ul><li>Once in the host, the virus must encounter </li></ul><ul><li>( recognize) a susceptible cell for the infection cycle to proceed </li></ul><ul><li>Susceptible host cells must : </li></ul><ul><ul><li>Contain receptors for the virus </li></ul></ul><ul><ul><li>Be permissive or capable of </li></ul></ul><ul><ul><li>supporting viral replication </li></ul></ul>
  28. 30. Virus Adsorption….. <ul><li>Host cell receptors must match the virus recognition sites for the virus to subsequently adsorb into the host cell </li></ul><ul><li>Most virus receptors are surface glycoproteins </li></ul>Host receptors Virus receptors ( glycoproteins)
  29. 31. Adsorption
  30. 32. Virus Penetration
  31. 33. Virus penetration <ul><li>Viral entry into host cells occurs through one of the following methods: </li></ul><ul><ul><li>Endocytosis </li></ul></ul><ul><ul><li>Direct fusion </li></ul></ul><ul><ul><li>Nucleic acid translocation </li></ul></ul>
  32. 34. Endocytosis <ul><li>All of the virus is engulfed </li></ul><ul><li>and enclosed in a vacuole </li></ul>
  33. 35. Direct Fusion <ul><li>Host cell membrane fuses with the virus </li></ul>
  34. 36. Nucleic acid translocation
  35. 37. Nucleic acid translocation Non enveloped virus injecting its nucleic acid to the host cell
  36. 38. Viral Uncoating
  37. 39. Viral Uncoating
  38. 40. Summary of Penetration/uncoating
  39. 41. Duplication and Synthesis
  40. 42. Duplication and Synthesis DNA and RNA viruses replicate in different manner.
  41. 43. DNA Replication
  42. 44. The Most Common DNA Viruses <ul><li>Adenoviruses </li></ul><ul><li>Cytomegalovirus </li></ul><ul><li>Epstein-Barr virus </li></ul><ul><li>Hepatitis B virus </li></ul><ul><li>Herpes simplex Types 1 &2 </li></ul><ul><li>Papovavirus </li></ul><ul><li>Varicella-Zoster virus </li></ul>
  43. 45. DNA Virus Replication-1 DNA dependent RNA polymerase is needed for the Transcription of mRNA from the DNA strand
  44. 46. DNA Virus Replication….2
  45. 47. DNA Virus Replication…3 The virus needs to code for proteins and enzymes that it can use in the Subsequent stages of its replication And assembly ( e.g. DNA polymerase, Capsid proteins.
  46. 48. DNA Virus Replication…4 DNA dependent DNA polymerase is Produce so that the DNA of the virus Can be replicated.
  47. 49. DNA Virus Replication…5
  48. 50. RNA Replication
  49. 51. The RNA Viruses <ul><li>Dengue viruses </li></ul><ul><li>Ebola virus </li></ul><ul><li>Picorna viruses </li></ul><ul><li>Hanta virus </li></ul><ul><li>Hepatitis A and C </li></ul><ul><li>HIV </li></ul><ul><li>Influenza virus </li></ul><ul><li>Mumps virus </li></ul><ul><li>Norwalk virus </li></ul><ul><li>Corona virus </li></ul><ul><li>Rotavirus </li></ul><ul><li>Rubeola Virus </li></ul><ul><li>RSV </li></ul>
  50. 52. RNA Virus Replication <ul><li>RNA viruses enter the host cell already in an RNA form and the virus cycle occurs entirely in the cytoplasm. </li></ul><ul><li>RNA viruses bring with them one of the following genetic messages: </li></ul><ul><ul><li>a positive sense genome ( +RNA) </li></ul></ul><ul><ul><li>a negative sense genome ( -RNA) </li></ul></ul><ul><ul><li>a ds RNA </li></ul></ul><ul><ul><li>ss RNA which is converted to DNA </li></ul></ul><ul><ul><li>( latent retroviruses) </li></ul></ul>
  51. 53. RNA Virus Replication….1
  52. 54. RNA Virus Replication…2 They have their own RNA dependent RNA Polymerase which it uses to transcribe from The –RNA the + RNA strand which is use In the making the protein
  53. 55. RNA Virus Replication…3 The + RNA strand is transcribe, the Complimentary copy is now a negative strand.
  54. 56. RNA Virus Replication…4 It can’t It can’t
  55. 57. RNA Virus Replication (Retrovirus)
  56. 58. RNA Virus Replication (Retrovirus)..
  57. 59. RNA Virus Replication (Retrovirus)..
  58. 60. Viral assembly
  59. 61. Viral assembly…
  60. 62. Viral Release
  61. 63. Viral Release Naked-nonenveloped and Complex viruses are released by cell lysis.
  62. 64. Viral Release….
  63. 65. Viral Release….
  64. 66. Release by budding
  65. 67. Viral Release….
  66. 68. Receptors Cell membrane Host cytoplasms RNA spikes SUMMARY OF VIRAL REPLICATION
  67. 69. Host range <ul><li>Spectrum of cells a virus can infect </li></ul><ul><ul><li>cell has to have a specific structure (receptor) on its surface for viral attachment </li></ul></ul><ul><ul><li>cell has to contain all of the enzymes and materials needed to produce new virions </li></ul></ul><ul><li>May be one species or many </li></ul><ul><ul><li>HIV (only humans) vs rabies (many animals) </li></ul></ul><ul><li>May be one tissue or many within a host </li></ul><ul><ul><li>Hepatitis (liver) vs polio (intestinal & nerve cells) </li></ul></ul>
  68. 70. Differences between phage and animal virus replication <ul><li>Animal virus replication is more complex than phage replication because host cells are more complex. </li></ul><ul><li>Animal viruses cannot inject their DNA. </li></ul><ul><li>Lysogeny for phage, latency for animal viruses </li></ul>
  69. 71. VIRAL CPE
  70. 72. Cytopathic effects- virus-induced damage to cells <ul><li>changes in size & shape </li></ul><ul><li>cytoplasmic inclusion bodies </li></ul><ul><li>nuclear inclusion bodies </li></ul><ul><li>cells fuse to form multinucleated cells </li></ul><ul><li>cell lysis </li></ul><ul><li>alter DNA </li></ul><ul><li>transform cells into cancerous cells </li></ul>
  71. 73. Cytopathic changes in cells
  72. 74. Inclusion body
  73. 75. Alteration of host membrane by insertion of viral proteins that trigger CMIR responses against the host cell Cytotoxic T cell will kill virus infected cells
  74. 76. Transformation or conversion of cell division to cells that divide indefinitely ( tumors ,warts) Induces hyperplasia of the host cells
  75. 77. Host Response to Viral Infections
  76. 78. <ul><li>Host Cell response includes : </li></ul><ul><ul><li>Antibody response </li></ul></ul><ul><ul><li>Cellular Immune response </li></ul></ul><ul><ul><li>Interferon production </li></ul></ul>
  77. 79. Antibody Response
  78. 80. Cellular Immune response
  79. 81. Interferons
  80. 82. Diagnostic Virology
  81. 83. How do we grow viruses? Obligate intracellular parasites require appropriate cells to replicate.
  82. 84. Growing animal viruses <ul><li>live animals </li></ul><ul><li>bird embryos – chicken, duck; intact, self-supporting unit, sterile, self-nourished </li></ul><ul><li>cell culture- cell lines </li></ul>
  83. 85. Virus laboratory
  84. 86. Cell Culture <ul><li>Cell culture is the process by which prokaryotic, eukaryotic or plant cell are grown under controlled conditions. </li></ul><ul><li>&quot;cell culture&quot; now , refers to the culturing of cells derived from multicellular eukaryotes, especially animal cells. </li></ul>
  85. 87. Cell lines <ul><li>Cells that are cultured directly from a subject are known as primary cells . </li></ul><ul><ul><li>primary cell cultures have limited lifespan </li></ul></ul><ul><ul><li>after a certain number of population doublings cells undergo the process of senescence and stop dividing, while generally retaining viability. </li></ul></ul><ul><li>An established or immortalised cell line has acquired </li></ul><ul><ul><li>the ability to proliferate indefinitely either through random mutation or deliberate modification, such as artificial expression of the telomerase gene </li></ul></ul><ul><ul><li>There are numerous well established cell lines representative of particular cell types. </li></ul></ul>
  86. 88. Established human cell lines <ul><li>One of the earliest human cell lines, descended from Henrietta Lacks , who died of cervical cancer . </li></ul><ul><li>The cultured HeLa cells shown below have been stained with Hoechst turning their nuclei blue. </li></ul>
  87. 89. Tissue Culture
  88. 90. Tissue Culture
  89. 91. No virus virus
  90. 92. Egg Inoculation
  91. 93. Egg inoculation …
  92. 94. Diagnosis of viral diseases <ul><li>More difficult than other agents </li></ul><ul><li>Consider overall clinical picture </li></ul><ul><li>Take appropriate sample </li></ul><ul><ul><li>Infect cell culture- look for characteristic cytopathic effects </li></ul></ul><ul><ul><li>Screen for parts of the virus </li></ul></ul><ul><ul><li>Screen for immune response to virus (antibodies) </li></ul></ul>
  93. 95. diagnosis
  94. 96. Thank you end of lecture !

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