wk6ans - Covel Peer Learning LS 4(Rachel Care Week 6 Week...

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Covel Peer Learning – LS 4 (Rachel Care) Week 6 Week 5/6 Material: 1. Transduction and Bacteriophage vocab: Week 5 a. How do we observe bacteriophage? Absence of bacteria = phage phenotype: plaques on a lawn of bacteria show where phage have successfully infected and killed a bacteria and spread to neighboring cells. b. Selection vs. screen: selection establishes conditions in which ONLY the desire mutant will grow (example: on a plate with kanamycin, ONLY kanR cells will grow) screen doesn’t kill anybody, ie replica plating c. What are the two classes of phage life cycles? 1. virulent (T2, T4) 2. temperate (lambda, P1, P22) i. Describe the 2 stages of the life cycle: lytic: phage DNA exists as plasmid, cell is turned into phage-constructing factory, cell dies upon lysis and release of new phage lysogenic: phage DNA single crossover into bacterial chromosome and lays dormant ii. Define “prophage”: the way the phage DNA exists in the lysogenic cycle, ie as single-crossedover in the bacterial chromosome (not homologous though!). Excises (also by SCO) to become lytic iii. Define “repressor”: a molecule that the prophage makes which prevents the prophage and other phage from starting a lytic cycle. Makes infected cells “immune” to new infection. iv. Define “zygotic induction”: how a lysogenic cell that is Hfr can make the F- cell its conjugating enter the lytic cycle. Because the F- cell DOESN’T make the repressor! So it gets the prophage and theres no repressor, so the prophage has nothing stopping it from entering the lytic cycle. d. What are the two types of transduction? 1. generalized 2. specialized (only occurs with TEMPERATE phages!) i. What are the two main differences between them? 1. what DNA is picked up: generalized: all bacterial DNA has an equal probability (“faulty head stuffing”) specialized: only DNA from near where the phage inserted (and is now excising) 2. when the DNA is picked up: generalized: during the packaging of the phage heads in the lytic cycle specialized: during the switch from lysogenic to lytic cycle (when the prophage excises) ii. Define “transductant”: cell resulting from gene transfer mediated by bacteriophage (ie not the original host, the cell that the phage made by the original host go infect)
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This note was uploaded on 03/28/2011 for the course LS 4 taught by Professor Ribaya during the Spring '08 term at UCLA.

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wk6ans - Covel Peer Learning LS 4(Rachel Care Week 6 Week...

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