Students_Lec10W2009

Students_Lec10W2009 - Lecture 9 Overview Viral (phage)...

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Lecture 9 Overview Viral (phage) genetics Mapping phage genes Transduction Testing for complementation vs. recombination Gene fine structure: Intragenic recombination
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Electron micrograph of phage T4 Figure 5-23
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Electron micrograph of phage infection Figure 5-24
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Structure and function of phage T4 Figure 5-22
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Lytic life cycle: T4 phage infecting E. coli Timeline t=0 virus attaches to E. coli surface, injects DNA. t=1’ viral DNA transcribed, translated, host processes stopped. t=5’ synthesize proteins to help copy viral DNA, copy viral DNA t=8’ protein for viral head and tail produced t=13’ assemble new phage t=25’ lyse E. coli cell, release phage
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Culturing lytic phage in the lab 1. Mix together bacteria and phage 2. Grow bacteria and phage 3. Wait for phage to lyse bacteria On plates: bacteria form “ lawn lysed cells form “ plaques plaques contain phage In liquid culture: bacteria make media cloudy lysis makes media clear lysis
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Multiplicity of Infection (MOI) The average number of phage particles that infect a single bacterial cell in a specific experiment Control MOI by controlling ratio of phage to bacterial cells Low MOI (<1 phage/cell) High MOI (>2 phage/cell)
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Viral phenotypes Like bacteria, use growth characteristics of clonal populations. single viruses too small to see. Plaque morphology: r+ r Host range: h+ h To score: combine phage with strains 1 and 2 of E. coli and plate.
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Mapping viral genes To “cross” viral strains, they must infect the same cell (high MOI) Infect strain 1 with hr+ and h+r Allow cells to grow and lyse Why strain 1? What genotypes are expected when the doubly infected cell lyses?
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Mapping viral genes To score viral genotypes, plate at low MOI on mix of strains 1 and 2. Why? Observed data
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Students_Lec10W2009 - Lecture 9 Overview Viral (phage)...

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