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Lecture 15

Lecture 15 - Genetic Recombination - BIOL308.pdf

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Department
Biology
Course
BIOL 308
Professor
Bruce Wolff
Semester
Fall

Description
Lecture 15Genetic Recombination contSitespecific Recombination2Occurs between sequences with a limited stretch of similarity involves specific sites Three typesfunctionsInversioneg Expression of alternate genes inversion of DNA sequencegene by DNA invertases1Insertioneg Infection insertion of bacteriophages in the bacterial genome by DNA integrase2Deletions eg Deletion o fbacteriophages from the bacterial genome different pathway for the 3bacteriumIn all three cases the components of the sitedirected recombination areRearrangement enzymesrecombinases in some cases accessory proteins are required1Sitespecific recombinases cleave and rejoin DNA using a covalent proteinDNA intermediateSo they have to haveSitespecific endonuclease activity cleavageaDNA ligase activity rejoiningbNote recombinases do recombinations cleave and ligate DNA using covalent protein DNA interactions through proteinDNA intermediate similar to what Topoisomerase does Exonuclease cuts from the end of the molecule 3 or 5 end where endonuclease cuts inside the DNA restriction enzymesRecombination site specific sequenceplaces of DNA exchange2Specifically recognized by recombinasePartially asymmetric nonpalindromicHave a percentage of homology not 100 homologousSite specific Recombination generalRecombination sites inDNA moleculeRearrangement enzymesexampleSame orientationTwo different DNA moleculesInsertion integration lambda integraseSame orientationSame DNA moleculeDeletion excisionInverted orientationSame DNA moleculeInversionDNA invertaseDNA deletions and insertionsUsed to recycle genesRecombination sites are recognized by specific recombinaseRecombination sites are flanking the geneeg Antibiotic resistance gene in direct orientationand on the same DNA moleculeStepsRecombination sites align next to each otherRecombinaseresolves the structure and cuts out deletes the geneExample bother theinsertionof the lambda phage DNA into bacterial genome and itsdeletionform it are accomplished by a sitespecific recombination event catalyzed by the lambda integrase enzyme insertion involves some bacterial enzyme as wellWhen the lambda DNA enters the cell the ends join to form a circular DNA moleculeLambda bacteriophage can mulitply in Ecoli by a lytic pathwaywill destroy cell or it can insert its DNA into bacterial genome and enter a latent prophage state NOTES FROM LECTURES Page 1
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