virus 1
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VIRUS
1. The development of virology2. TMV virus3. Lambda phage4. 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 1900’s
Established that viruses propagate only in living cells, i.e. obligate intracellular parasitesViruses capable of destroying Staphylococci identified
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The development of virology
1917
Viruses capable of destroying dysentery bacilli identifiedBacterial viruses now called bacteriophages.
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The development of virology
1930’s
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 acidViruses 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, TMVDNA virus e.g. bacteriophageRNA 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 acidThe protein protects the nucleic acid from hostile environmental conditionsThe 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 15nm94% 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 contaminatedSterilisation of soil used for seed bedsHygienic handling of crops by workersUse resistant varieties of crops
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The lambda phageAlso known as:
T4-phage
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The lambda phageAn example of a bacteriophage (A virus that uses bacterium as its host)Invades the bacterium Escherichia coli
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The lambda phageCan destroy the host cell or insert its DNA into the bacterial chromosome and remain dormant for several generations
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The lambda phageConsists of a head, containing a double stranded DNA molecule wrapped around a core of protein surrounded by a polyhedral capsule and a helical tail.