The baseplate of the virion attaches to the entry

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Adsorption: The phage attaches to target cell adhesion receptors through its tail fibers.The baseplate of the virion attaches to the entry receptor.Ejection of the viral DNA into host cell cytoplasm by long flexible tail ejection system.Transcription and translation of early genes.Replication of genomic DNA by theta replication.Replication of genomic DNA by rolling circle.Transcription and translation of late genes.Assembly of empty procapsids and viral genome packaging.Mature virions are released from the cell by lysis.The Role of Lysogeny in Human Disease:Occasionally, phage genes in the bacterial chromosome cause the production of toxins or enzymes that the bacterium would not otherwise haveLysogenic conversion: when a bacterium acquires a new trait from its temperate phage:• Corynebacterium diphtheriae - diphtheria toxin• Vibrio cholerae - cholera toxin• Clostridium botulinum - botulinum toxinVirophages: parasitize other viruses that are infecting the same host cell they infectSection 5.4: Techniques in Cultivating and Identifying Animal VirusesViruses require living cells as their “medium”:In vivo: laboratory-bred animals and embryonic bird tissuesIn vitro: cell or tissue culture methods Primary purposes of viral cultivation:• Isolate and identify viruses in clinical specimens• Prepare viruses for vaccines• Do detailed research on viral structure, multiplication cycles, genetics, and effects on host cellsUsing Live Animal Inoculation:Specially bred strains of white mice, rats, hamsters, guinea pigs, and rabbits are the usual choices for viral cultivationOccasionally, invertebrates such as insects or nonhuman primates are used
Because viruses exhibit host specificity, certain animals can propagate viruses more readily than othersUsing Bird Embryos:Bird eggs containing embryos:• Intact and self-supporting unit• Sterile environment• Contain their own nourishmentChicken, duck, and turkey eggs are the most common choices forinoculationViruses are injected through the eggshell by drilling a small hole or making a small windowThe cells within chicken eggs are used to culture different types of viruses.Viruses can be replicated in various locations within the egg, including the chorioallantoic membrane, the amniotic cavity, and the yolk sac.Using Cell (Tissue) – Culture TechniquesSimple and effective way to grow populations of isolated animal cells in culture Isolated animal cells are grown in vitroin cell or tissue culture rather than in an animal or eggCell culture, or tissue culture:• Grown in sterile chambers with special media that contain the correct nutrients for cells to survive• Cells form a monolayer, or single, confluent sheet of cells that supports viral multiplication• Allows for the close inspection of culture for signs of infectionDetection of Viral Growth in Culture:Observation of degeneration and lysis of infected cellsPlaques: areas where virus-infected cells have been destroyed show up as clear, well-defined patches in the cell sheet:• Plaques are the visible manifestation of cytopathic effects (CPEs)o

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