Chapter 13 Outline

Chapter 13 Outline - Chapter 13 The Viruses and Virus-Like...

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Chapter 13 The Viruses and Virus-Like Agents 13.1 Foundations of Virology Many Scientists Contributed to the Early Understanding of Viruses Dimitri Ivanowsky and Martinus Beiherinck studied the tobacco mosaic virus Walter Reed studied foot-and-mouth disease and yellow fever Frederick Twort and Felix d’Herelle studied bacteriophages In the 1930s, it was discovered that viruses are nonliving agents composed of nucleic acid and protein Alice M. Woodruff and Ernest W. Goodpasture developed a culture technique using chicken eggs 13.2 What Are Viruses? Viruses Are Tiny Infectious Agents Viruses are small, obligate intracellular parasites They lack the machinery for generating energy and large molecules They need a host eukaryote or prokaryote to replicate The viral genome contains either DNA or RNA, but not both The capsid is the protein coat, made up of capsomeres The nucleocapsid is the capsid with its enclosed genome Some capsid proteins are spikes that help the virus attach to and penetrate the host cell Naked viruses are composed only of a nucleocapsid Viruses surrounded by an envelope are enveloped viruses A virion is a completely assembled, infectious virus outside its host cell Viruses Are Grouped by Their Shape Helical viruses have helical symmetry Isocahedral viruses have isocahedral symmetry Viruses that have both helical and isocahedral symmetry have complex symmetry Viruses Have a Host Range and Tissue Specificity A host range refers to what organisms the virus can infect Host range depends on capsid structure Many viruses infect certain cell or tissue types within the host (tissue tropism) 13.3 The Classification of Viruses Nomenclature and Classification Do Not Use Conventional Taxonomic Groups Viruses can be named according to a number of different conventions The International Committee on Taxonomy of Viruses (ICTV) is developing a classification system DNA viruses contain single- or double-stranded DNA genomes RNA viruses contain single- or double-stranded RNA genomes + strand RNA viruses have mRNA genomes – strand RNA viruses have RNA strands that would be complementary to mRNA Retroviruses are replicated indirectly through a DNA intermediate 13.4 Viral Replication and Its Control The Replication of Bacteriophages Is a Five-Step Process T-even group bacteriophages are virulent viruses that carry out a lytic cycle of infection The phage nucleic acid contains only a few of the genes needed for viral synthesis and
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Chapter 13 Outline - Chapter 13 The Viruses and Virus-Like...

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