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Virus 1


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Virus 1

  1. 1. VIRUS <ul><li>The development of virology </li></ul><ul><li>TMV virus </li></ul><ul><li>Lambda phage </li></ul><ul><li>HIV </li></ul>
  2. 2. The development of virology <ul><li>Start of 20 th centaury </li></ul><ul><li>Infectious diseases attributed to parasitic fungi and bacteria </li></ul>
  3. 3. The development of virology <ul><li>1892 </li></ul><ul><li>Tobacco mosaic disease induced in healthy plants by rubbing their leaves with juices from infected plants after filtering through bacterial filters </li></ul>
  4. 4. The development of virology <ul><li>1892 </li></ul><ul><li>Foot and mouth disease shown to be passed on in bacterial filtered fluids from infected animals </li></ul>
  5. 5. The development of virology <ul><li>1898 </li></ul><ul><li>Recognised that there must be a “new” type of infectious agent – the term “virus” introduced </li></ul>
  6. 6. The development of virology <ul><li>Early 1900’s </li></ul><ul><li>Established that viruses propagate only in living cells, i.e. obligate intracellular parasites </li></ul><ul><li>Viruses capable of destroying Staphylococci identified </li></ul>
  7. 7. The development of virology <ul><li>1917 </li></ul><ul><li>Viruses capable of destroying dysentery bacilli identified </li></ul><ul><li>Bacterial viruses now called bacteriophages . </li></ul>
  8. 8. The development of virology <ul><li>1930’s </li></ul><ul><li>Established that viruses are particulate, virus particles called virions . </li></ul>
  9. 9. The development of virology <ul><li>1935 </li></ul><ul><li>Tobacco mosaic virus (TMV) purified </li></ul>
  10. 10. The development of virology <ul><li>1936 </li></ul><ul><li>Established that TMV is a nucleo-protein capable of crystallization. </li></ul><ul><li>This suggests a simplicity and regularity to their structure </li></ul>
  11. 11. The development of virology <ul><li>Subsequent studies </li></ul><ul><li>Possible to separate the protein and nucleic acid of viruses and demonstrate that the nucleic acid component alone is capable of initiating infection. </li></ul>
  12. 12. The development of virology <ul><li>Structural and chemical composition of viruses </li></ul><ul><li>Understanding virus structure has been dependent upon the development of such methods as chromatography, electrophoresis, density gradient centrifugation, electron microscopy and X-ray diffraction </li></ul>
  13. 13. The development of virology <ul><li>Structural and chemical composition of viruses </li></ul><ul><li>Simplest viruses, e.g. TMV, consist of only protein and nucleic acid </li></ul><ul><li>Viruses only ever have one type of nucleic acid </li></ul>
  14. 14. The development of virology <ul><li>Three basic virus groups </li></ul><ul><li>RNA virus e.g. Tobacco mosaic virus, TMV </li></ul><ul><li>DNA virus e.g. bacteriophage </li></ul><ul><li>RNA retrovirus e.g. HIV </li></ul>
  15. 15. The development of virology <ul><li>Most of the proteins in a virus occur as a coat, called a caspid, surrounding the nucleic acid </li></ul><ul><li>The protein protects the nucleic acid from hostile environmental conditions </li></ul><ul><li>The protein also aids the penetration of the host cell. </li></ul><ul><li>The outer coat (the caspid) is made out of sub-units called capsomeres, arranged in a helical pattern </li></ul>
  16. 16. Tobacco Mosaic Virus (TMV) <ul><li>Rod shaped 300nm long, diameter 15nm </li></ul><ul><li>94% protein, </li></ul><ul><li>6% RNA </li></ul>
  17. 17. Tobacco Mosaic Virus (TMV) <ul><li>Attacks tomato, blackcurrant, potato, orchid and tobacco. </li></ul><ul><li>Causes irregular mottled patches to appear on leaves of plants which indicate areas where cells and tissues have been killed by the virus </li></ul>
  18. 18. Tobacco Mosaic Virus (TMV) <ul><li>Carried on seed coats, by grasshoppers and by other mechanical means </li></ul>
  19. 19. Tobacco Mosaic Virus (TMV) <ul><li>Control measures include </li></ul><ul><li>Avoidance of growing susceptible crops in soil known to be contaminated </li></ul><ul><li>Sterilisation of soil used for seed beds </li></ul><ul><li>Hygienic handling of crops by workers </li></ul><ul><li>Use resistant varieties of crops </li></ul>
  20. 20. The lambda phage <ul><li>Also known as: </li></ul><ul><li>T4-phage </li></ul>
  21. 21. The lambda phage <ul><li>An example of a bacteriophage (A virus that uses bacterium as its host) </li></ul><ul><li>Invades the bacterium Escherichia coli </li></ul>
  22. 22. The lambda phage <ul><li>Can destroy the host cell or insert its DNA into the bacterial chromosome and remain dormant for several generations </li></ul>
  23. 23. The lambda phage <ul><li>Consists of a head, containing a double stranded DNA molecule wrapped around a core of protein surrounded by a polyhedral capsule and a helical tail. </li></ul>