VIRUS

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VIRUS

• The development of virology
• TMV virus
• Lambda phage
• HIV

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The development of virology

• Start of 20th centaury
• Infectious diseases attributed to parasitic fungi
  and bacteria

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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

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The development of virology

• 1892
• Foot and mouth disease shown to be passed on in
  bacterial filtered fluids from infected animals

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The development of virology

• 1898
• Recognised that there must be a new type of
  infectious agent the term virus introduced

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The development of virology

• Early 1900s
• Established that viruses propagate only in living
  cells, i.e. obligate intracellular parasites
• Viruses capable of destroying Staphylococci
  identified

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The development of virology

• 1917
• Viruses capable of destroying dysentery bacilli
  identified
• Bacterial viruses now called bacteriophages.

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The development of virology

• 1930s
• Established that viruses are particulate, virus
  particles called virions.

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The development of virology

• 1935
• Tobacco mosaic virus (TMV) purified

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The development of virology

• 1936
• Established that TMV is a nucleo-protein capable
  of crystallization.
• This suggests a simplicity and regularity to
  their structure

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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.

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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

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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

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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

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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

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Tobacco Mosaic Virus (TMV)

• Rod shaped 300nm long, diameter 15nm
• 94 protein,
• 6 RNA

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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

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Tobacco Mosaic Virus (TMV)

• Carried on seed coats, by grasshoppers and by
  other mechanical means

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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

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The lambda phage

• Also known as
• T4-phage

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The lambda phage

• An example of a bacteriophage (A virus that uses
  bacterium as its host)
• Invades the bacterium Escherichia coli

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The lambda phage

• Can destroy the host cell or insert its DNA into
  the bacterial chromosome and remain dormant for
  several generations

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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.