ESPM 131 Viruses

ESPM 131 Viruses - Separated as fuction of their hosets At...

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ESPM 131 Viruses Viruses are molecular sharks, a motive w/o a mind. – Richard Preston Introduction Infectious agents Acellular Only one type of nucleiv acid: DNA or RNA Reproduce within living cells Virus ( latin) = poison, toxin Ivanovski (1982) and Beijerinick (1898): first discoveries Lwoff (1957): good working definition “ viruses are infectious agents made up of nucleic acids and proteins unable to grow independently” Gerneal Properties of Viruses - 20-200 nm in size - only 10 to 200 genes are coded - Considered as ‘ non-living organisms” by some - Obligate intracellular parasites - Wide range of hosts - One or more molecules of DNA or RNA enclosed in protein coat - Exist in two phases: Extracellular = virion & Intracellular - Viruses differ from living cells in 3 ways: - simple , acellular organization - Presence of DNA or RNA In summary Viruses differ from living cells in 3 ways
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Unformatted text preview: Separated as fuction of their hosets At present , 1500 virus species described Animal viruses: Plaque formation Cytopathic effects the shape of the cell changed Bacteriophages-In broth cultures of young bacterial cells-In agar cultures on lawn of bacterial cells plague formation Plant viruses Plant tissue cultures Whole plants Structure of viruses Nucleocapsid core: either DNA or RNA Protein coat called capsid Four general morphological types -Icosahedron-Helical-Most complex ; large bacteriophage T2, T4, T6-Virus Replication-Virulent phage: 1. attachment ( adsorption) 2. penetration ( injection) 3. synthesis of nucleic acid and protein 4. assembly and packaging 5. release ( lysis) Burst size: number of virions released Virulent viruses Temperate viruses: state called lysogenry Virus Ecology Microorganism viruses persist...
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ESPM 131 Viruses - Separated as fuction of their hosets At...

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