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Unformatted text preview: 10/8/2010 1 Chapter 19 VIRUSES Mobile genetic elements Fig. 19-1 0.5 μm Viruses • Infectious particles consisting of nucleic acid enclosed in protein coat & sometimes a membranous envelope • Obligate intracellular parasites • Use genetics to take over of a cell But are they alive? Viruses: Are they alive? A debated issue • Employ DNA or RNA (single or double stranded) • Contain proteins • Reproduce but not without use of host cells’ genetic machinery • One virus may produce protein coated tails without host • Evolve in response to their environment (influenza, H5N1avian , H1N1swine) • Some can be crystallized! “A borrowed life” 10/8/2010 2 What is Biology? • Study of living organisms descended from single-celled ancestor that evolved 4 billion years ago • Living organism consists of one or more cells • Contains genetic information • Uses genetic info to reproduce themselves • Are genetically related & have evolved • Can convert molecules from environment into new biological molecules • Can extract energy from environment and use it to do biological work • Can regulate their internal environment Discovery international science • Adolf Mayer (1883) & Tobacco mosaic disease • Transmit disease from plant to plant leaf • Dimitri Ivanowsky (1890) filtered sap infectious • Maritinus Beijerinck (1898) demonstrated infectious agent could reproduce • Wendell Stanley (1935) crystallized infectious particle: TMV Fig. 19-2 RESULTS 1 2 3 Extracted sap from tobacco plant with tobacco mosaic disease Passed sap through a porcelain filter known to trap bacteria Rubbed filtered sap on healthy tobacco plants 4 Healthy plants became infected Fig. 19-3a (a) Tobacco mosaic virus 20 nm 18 250 nm Capsomere of capsid RNA 10/8/2010 2 What is Biology? • Study of living organisms descended from single-celled ancestor that evolved 4 billion years ago • Living organism consists of one or more cells • Contains genetic information • Uses genetic info to reproduce themselves • Are genetically related & have evolved...
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This note was uploaded on 02/06/2011 for the course BIO 120 at USC.