Transcript Document
Introduction
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What is a virus?
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How are viruses are different from other organisms?
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Are viruses alive?
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The history of virology
how we think about viruses
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Techniques used to study viruses
Principles of Molecular Virology © Elsevier, 2011.
What are viruses?
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Viruses are submicroscopic, obligate intracellular parasites
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Most too small to be seen by optical microscopes Largest virus known (Mimivirus) = 400 nm diameter, smallest bacteria (Mycoplasma) = 200 nm
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Largest virus genome (Mimivirus, 1.2 Mbp) twice as big as smallest bacterial genome (Mycoplasma genitalium, 0.58 Mbp)
Principles of Molecular Virology © Elsevier, 2011.
How viruses are unique
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Virus particles are produced from the assembly of preformed components, other biological agents grow from an increase in the integrated sum of their components and reproduce by division
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Virus particles (virions) do not grow or divide
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Viruses lack the genetic information that encodes tools necessary for the generation of metabolic energy or protein synthesis (ribosomes)
Principles of Molecular Virology © Elsevier, 2011.
Are viruses alive?
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Viruses do not reproduce by division but are assembled from preformed components
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Viruses cannot make their own energy or proteins
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A virus-infected cell is more like a factory than a womb
© Elsevier, 2011.
Principles of Molecular Virology
The history of virology
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First written record of virus infection ~ 3700 BC - paralytic poliomyelitis
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Smallpox endemic in China by 1000 BC
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Edward Jenner, 14th May 1796 - smallpox vaccination
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Robert Koch and Louis Pasteur, 1880s - germ theory of disease
Principles of Molecular Virology © Elsevier, 2011.
The history of virology
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1892: Dimitri Iwanowski "filterable particles”
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- smaller than bacteria 1898: Martinus Beijerinick - tobacco mosaic virus
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- "soluble living germ" 1898: Freidrich Loeffler and Paul Frosch
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- foot-and-mouth disease in cattle 1909: Karl Landsteiner and Erwin Popper
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- poliomyelitis in humans Frederick Twort (1915) and Felix d’Herelle (1917) - bacteriophages
Principles of Molecular Virology © Elsevier, 2011.
Living host systems
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1881: Louis Pasteur - rabies vaccine from rabbits
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1900: Walter Reed - yellow fever caused by a virus spread by mosquitoes
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Animal host systems still have their uses in virology:
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To produce viruses that cannot be effectively studied in vitro (e.g. hepatitis B virus)
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To study the pathogenesis of virus infections (e.g. HIV and SIV)
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To test vaccine safety (e.g. oral poliovirus vaccine)
Principles of Molecular Virology © Elsevier, 2011.
Living host systems
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1980's: transgenic animals which which carry the genes of other organisms
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Transgenics are useful for understanding the pathogenesis of viruses, prions
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Principles of Molecular Virology
Cell Culture Methods
1949: John Enders propagates poliovirus in human cells 1950s and 1960s: identification and isolation of many viruses 1952: Renato Dulbecco plaque assay
Principles of Molecular Virology © Elsevier, 2011.
Serological/Immunological Methods
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1941: George Hirst - haemagglutination of red blood
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cells by influenza virus Improved detection methods for viruses: Complement fixation tests Radioimmunoassays Immunofluorescence (direct detection of virus antigens in infected cells or tissue) Enzyme-linked immunosorbent assays (ELISAs) Radioimmune precipitation Western blot assays
Principles of Molecular Virology © Elsevier, 2011.
Serological/Immunological Methods
Principles of Molecular Virology © Elsevier, 2011.
Monoclonal antibodies
Principles of Molecular Virology © Elsevier, 2011.
Ultrastructural Studies
Centrifugation of virus particles
Principles of Molecular Virology © Elsevier, 2011.
Ultrastructural Studies
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Spectroscopy - light-scattering properties
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X-ray diffraction
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Nuclear magnetic resonance (NMR)
Principles of Molecular Virology © Elsevier, 2011.
Ultrastructural Studies
Principles of Molecular Virology © Elsevier, 2011.
Electron Microscopy
Principles of Molecular Virology © Elsevier, 2011.
Molecular Biology
Experimental techniques used to study the structure and function of biomolecules and their interactions Focus on the virus genome: • • • Molecular cloning Nucleotide sequencing Microarrays
© Elsevier, 2011.
Principles of Molecular Virology
Nucleic acid hybridization
Blotting and probing for detection of DNA (Southern blot), RNA (Northern blot), proteins (Western blot)
Principles of Molecular Virology © Elsevier, 2011.
Polymerase chain reaction (PCR)
Principles of Molecular Virology © Elsevier, 2011.
Bioinformatics
Principles of Molecular Virology © Elsevier, 2011.
Further Reading
Alberts, B., Bray, D., Hopkin,K., Johnson, A., Lewis, J., Raff, M., Roberts, K., Walter, P. and Johnson, A. (2009). Essential Cell Biology. 3rd Edition. Garland Science, New York. ISBN 0815341296 Forterre, P. (2010) Defining life: the virus viewpoint. Orig Life Evol Biosph. 40(2): 151-160 Hendrix, R.W. (2003). Bacteriophage genomics. Current Opinion in Microbiology, 6: 506 –511 Lesk, A. Introduction to Bioinformatics. (2008) OUP Oxford; 3rd edition Moreira, D., and López-García, P. (2009). Ten reasons to exclude viruses from the tree of life Nature Reviews Microbiology, 7 (4): 306-311 Primrose, S. and Twyman, R. Principles of Gene Manipulation and Genomics. (2006) Wiley-Blackwell 7th Edition Raoult D, Forterre P. (2008) Redefining viruses: lessons from Mimivirus. Nat Rev Microbiol. 6 (4): 315-319 Sompayrac, L. How the Immune System Works. (2008) Wiley-Blackwell. 3rd edition Villarreal L. (2004) Are viruses alive? Scientific American 291 (6): 100-105
Principles of Molecular Virology © Elsevier, 2011.