497A Lecture 2 & 3

497A Lecture 2 & 3 - 12/28/10 Lectures 2 & 3...

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12/28/10 1 Lectures 2 & 3 The (Basic) Biology of Viruses More Shameless Self-Publicity Discovery & Classification of Viruses
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12/28/10 2 1500 B.C. Early evidence of polio? 1200 A.D. Early evidence of rabies Viruses in Human History • Jenner undertook the first vaccination by deliberately infecting patients with the cowpox virus ( Vaccinia ) protecting them against the more serious smallpox virus. • But Jenner had no idea that a virus was a ‘living’ agent • Viruses are obligate parasites (cannot replicate without a host cell - animal, plant, bacterium). The Discovery of Viruses • “Virus” is derived from the Greek word for “poison”. Viruses were first “described” by Edward Jenner (English doctor) in 1798, although there may be earlier descriptions in the Chinese and Islamic worlds. • 1892: Dimitri Ivanofsky passed infected sap through unglazed porcelain filter and found it retained its infectious properties. Still not clear that it was a living agent - could be a toxin The Discovery of Viruses • 1898: Martinus Beijerinck showed that the diluted sap could regain its ‘strength’ after replication in living, growing plant tissue. • 1879: Adolf Mayer inoculated healthy plants with the juice of ground up leaves from plants that had tobacco mosaic disease. • 1898 – 1915: Several ‘filterable’ agents isolated e.g. FMDV (1898), Myxoma (1898), Yellow Fever (1901), Rabies (1903), Polio (1909). Tobacco Mosaic Virus (TMV) The science of virology didn’t begin until the junction of the 19/20th centuries
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12/28/10 3 • 1915 - Felix d’Herelle demonstrated that plaques appeared in cultures of Shigella killing the bacteria in the petri dish. • Plaques appeared on the 4th day coinciding with recovery in the patient. • D’Herelle named these viruses of bacteria “bacteriophages” and reasoned that they were particulate because they formed plaques. The Discovery of Viruses: Bacteriophage • The Englishman Frederick Twort also did seminal early work on bacteriophage Bacteriophages Have Played a Key Role in Molecular Biology • The active component of the bacteriophage that transmits the infective characteristic is the DNA. There is a correlation between DNA and genetic information. “All the World’s a Phage” • Estimated to be ~10 30 bacteria in the world • If there are ~10 bacteriophage for every bacterium, then there are ~10 31 bacteriophage in the world (~50 million viruses per millilitre of seawater) • This would bacteriophage the most common source of DNA on earth! Hendrix RW, Smith MCM, Burns RN, Ford ME & Hatfull GF. (1999). Evolutionary relationships among diverse bacteriophage and prophages: All the world’s a phage. Proc.Natl.Acad.Sci.USA 96 , 2192-2197. • New viruses are discovered on a very regular basis (particularly since the rise of metagenomics)
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12/28/10 4 What is a Virus?
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497A Lecture 2 & 3 - 12/28/10 Lectures 2 & 3...

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