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3C3

3C3. Viral replication results in genetic variation in virus and host. Viral replication is different from other types. Reproductive cycles. Attachment or adsorption Target part of bacterial outer surface Penetration or injection T4 pierces cell wall to inject viral genome Synthesis

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3C3

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  1. 3C3 Viral replication results in genetic variation in virus and host

  2. Viral replication is different from other types

  3. Reproductive cycles • Attachment or adsorption • Target part of bacterial outer surface • Penetration or injection • T4 pierces cell wall to inject viral genome • Synthesis • Phage may immediately take over the cell’s replication and protein synthesis enzymes to synthesize viral components

  4. Assembly • Assembly of components • Release • Mature virus particles are released through enzyme lysing host or budding through host cell wall • Eclipse period • Time between adsorption and the formation of new viral particles • If a cell is lysed at this point, few if any active virions can be released

  5. HIV Infection Cycle • Model for animal viruses • Details may vary for other viruses • Attachment • Virus only attacks CD4+ cells • Viral gp120 attaches to CD4 protein on macrophages and CD4+ cells • Coreceptors like CCR5 affect likelihood of entry • Entry through fusion pore

  6. Replication • Reverse transcriptase converts virus RNA to double-stranded DNA • Mutations common in process • DNA is incorporated into host genome • Variable period of dormancy • Assembly • Making many copies of virus • Release • New viruses exit by budding

  7. Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.

  8. Lytic cycle • Virus lyses the infected host cell • Virulent or lytic phages • Lysogenic cycle • Virus does not immediately kill infected cell • Integrate virus nucleic acid into host cell genome – prophage • Integration allows a virus to be replicated along with the host cell’s DNA as the host divides • Temperate or lysogenic phage

  9. Binal phage lambda (λ) of E. coli • Best studied biological particle • When phage λ infects a cell, the early events constitute a genetic switch that will determine whether the virus is lytic or lysogenic • Induction during stress • Prophage can be excised and begins lytic cycle • Requires turning on the gene expression necessary for the lytic cycle

  10. Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at http://get.adobe.com/flashplayer.

  11. Phage conversion • Phenotype or characteristics of the lysogenic bacterium is altered by the prophage • Vibriocholerae phage conversion • Lysogenic phage introduced a gene coding for cholera toxin • Gene became incorporated into host genome • Converts harmless bacteria into disease-causing form

  12. Mechanisms that increase genetic variation • http://www.youtube.com/watch?v=UjMn4oHfYL4

  13. Viral replication • http://www.youtube.com/watch?v=EqK1CYYQIug

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