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