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Lecture 3.26 Notes

Lecture 3.26 Notes - Notes Viral Replication General...

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Notes 3/26/10 Viral Replication General Features 1. Adsorption – virus binds to cell 2. Entry – viral nucleic acid enters cell cytoplasm 3. Viral gene expression and replication 4. Assembly (morphogenesis) 5. Release of progeny One-step growth curve of virus replication Eclipse – uncoating and entry of viral genome o Early gene expression – avoidance of host restriction and host takeover o Genome replication o Synthesis of viral structural proteins Maturation – assembly and release of infectious progeny o Various mechanisms of release Cell lysis (lytic viruses) Budding (enveloped viruses) Secretion – often employs normal secretory mechanisms – common for animal viruses Viral Attachment and Penetration Attachment - most common basis for host specificity: host range determined by presence of appropriate receptor o Protein(s) on virion interact with specific protein(s) on target cell o Cell receptors – normal surface components Proteins (or glycoproteins) Carbohydrates Lipids Lipoproteins o Also basis for tissue tropism in metazoans Penetration o Entry of viral genome often involves action of viral proteins o Viral program of expression requires permissive cell o Many different strategies for penetration Enveloped anima viruses often uncoated at cytoplasmic membrane releasing genome into cytoplasm or nucleus Naked viruses often uncoated inside cytoplasm o Tailed bacteriophage attachment and penetration Special adaptations required for entry into organisms with cell walls T4 strategy Tail fibers interact with outer membrane
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polysaccharides Tail fibers retract and tail pins make contact w/ cell wall Lysozyme-like activity loosens up peptidoglycan Tail sheath contracts and viral DNA passes into cytoplasm Host restriction systems o Animal cells contain innate and adaptive immune responses to block viral replication o Prokaryotes rely on specific DNA destruction systems (restriction endonucleases) Viral adaptations Modification of nucleic acids – methylation, hydroxymethylation, glycosylation (T2, T4, T6) Viral inhibition of restriction systems (T3, T7) Production of Viral Nucleic Acids and Protein: Example: Bacteriophage T4 Genome is terminally redundant and (within population) circularly permuted o Progeny genomes contain 3’ overhangs due to removal of DNA replication primers o Recombination within terminal redundancy creates long concatamers o Heedful packaging creates “circular permutation” (i.e. – different progeny virions contain different terminal redundancies.
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