Chapter 19 Viruses

Chapter 19 Viruses - hapter19 Viruses...

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hapter 19 Viruses
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Overview: A Borrowed Life Viruses called bacteriophages can infect and set in motion a genetic takeover of bacteria, such as Escherichia coli Viruses lead “a kind of borrowed life” between life-forms and chemicals The origins of molecular biology lie in early studies of viruses that infect bacteria
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Concept 19.1: A virus consists of a nucleic acid  surrounded by a protein coat Viruses were detected indirectly long before they were actually seen
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The Discovery of Viruses:  Scientific Inquiry Tobacco mosaic disease stunts growth of tobacco plants and gives their leaves a mosaic coloration In the late 1800s, researchers hypothesized that a particle smaller than bacteria caused the disease In 1935, Wendell Stanley confirmed this hypothesis by crystallizing the infectious particle, now known as tobacco mosaic virus (TMV)
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Structure of Viruses Viruses are not cells Viruses are very small infectious particles consisting of nucleic acid enclosed in a protein coat and, in some cases, a membranous envelope
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Viral Genomes Viral genomes may consist of either Double- or single-stranded DNA, or Double- or single-stranded RNA Depending on its type of nucleic acid, a virus is called a DNA virus or an RNA virus
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Capsids and Envelopes A capsid is the protein shell that encloses the viral genome Capsids are built from protein subunits called capsomeres A capsid can have various structures
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Some viruses have membranous envelopes that help them infect hosts These viral envelopes surround the capsids of influenza viruses and many other viruses found in animals Viral envelopes, which are derived from the host cell’s membrane, contain a combination of viral and host cell molecules
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Bacteriophages , also called phages , are viruses that infect bacteria They have the most complex capsids found among viruses Phages have an elongated capsid head that encloses their DNA A protein tail piece attaches the phage to the host and injects the phage DNA inside
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Concept 19.2: Viruses reproduce only in host cells
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This note was uploaded on 01/06/2012 for the course BIO 1406 taught by Professor Bethanypereira during the Fall '10 term at Collins.

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Chapter 19 Viruses - hapter19 Viruses...

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