Laboratory Exercise - Weeks 7 and 8.pdf

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University of Toronto Scarborough
Biological Sciences
Daman Bawa

Brunt 2011 Modified from Riggs 2007 Laboratory week 7 and 8 Gene regulation in bacteria the lac operonOutlineWeek 7A induction of the lac operon in wild type and mutant strains of Ecoli Week 7B lac operoninterpretation of Week 7A data and designexperiment to testregulation of lac operon Week 8A carry out your group experiment Week 8B data analysis of group experiment and restriction mapping assingmentObjectivesRecognizethe typeof mutation present based on theinduction ofbetagalactosidase productionTo understand the use ofcolourimetric substratesinenzyme assaysTounderstand the use ofenzyme activity as amarker for gene expressionTo understand the mechanism of controlunderlying induction of the lacoperonBackground Transcription involves transacting factors eg RNA polymerase and other factors moving to and interacting with specific DNAregulatory sequences cisacting sequences to alter gene expressionThere are a wide variety of sequencespecific DNA binding proteins transcription factors that coordinate transcription of specific genes or sets of genes needed by the cell or organism to respond to stimuliUsually the regulatory DNA sequences lie upstream from the gene in the region called the promoter More than one transcription factor usually act together to control the expression of a gene Sometranscription factors are negative regulators repressors and some are positive regulators inducers Often very rapid changes can occur in response to changes in the environment of the cell Responses to the presence or absence of hormones growth factors and other metabolites as well as changes in physical parameters such as temperature can quite dramatically alter signal transduction to condition an appropriate response Prokaryotes have been extensively studied by molecular biologists and the lac operonof Escherichia coli was one of the first regulatory systems studied The operon model defined by Jacob and Monod 1961 was a significant development in understanding gene regulation They received the Nobelprize in 1965 for their work The suggestion that there can be coordinated control of the expression of multiple genes led researchers to look for similar genetic units controlling other enzyme systemsThe lac operon is activated in bacteria in the presence of lactose when glucose levels are lowThe lac operon coordinates the catabolism of lactose into the simpler sugars galactose and glucose the preferred carbon source The enzyme Beta1
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