Chapter%2019%20Outline - Chapter19Viruses ABorrowedLife

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A Borrowed Life Viruses lead “a kind of borrowed life” between life-forms and chemicals Bacteriophages  Infect and set in motion a genetic takeover of bacteria   The origins of molecular biology lie in early studies of viruses that infect bacteria Viruses were detected indirectly long before they were actually seen Fig. 19-1 The Discovery of Viruses In the late 1800s, researchers hypothesized that a particle smaller than bacteria  caused Tobacco mosaic disease  In 1935, Wendell Stanley confirmed this hypothesis by crystallizing the infectious  particle  Fig. 19-2 Structure of Viruses Viruses are not cells Viruses are very small infectious particles consisting of  nucleic acid a protein coat  some have a membranous envelope Viral Genomes Viral genomes may consist of either  Double- or single-stranded DNA  Double- or single-stranded RNA Depending on its type of nucleic acid, a virus is called a DNA virus or an RNA  virus Capsids and Envelopes Capsid  protein shell that encloses the viral genome are built from protein subunits called  capsomeres   can have various structures Fig. 19-3
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Chapter%2019%20Outline - Chapter19Viruses ABorrowedLife

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