.net/bbcswebdav/pid-2730312-dt-content-rid-20530634_1/courses/82740-1552/F09Exam
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.net/bbcswebdav/pid-2730312-dt-content-rid-20530634_1/courses/82740-1552/F09Exam2.pdf page 3 of 7 4. You are interested in studying the transcriptional regulation of a gene expressed in the gut called Smrtl. The promoter for Smrtl contains binding sites for two transcriptional regulators called A and B. Proteins A and B bind to the promoter by recognizing specific sequences called binding sites. The binding sites for these proteins are diagrammed in the figure. As shown, the binding sites for protein A and B overlap; it has been demonstrated that proteins A and B cannot bind simultaneously. It has also been demonstrated Experiment Binding site Glucose Smrti mRNA that protein A is an allosteric protein that is number B regulated by the sugar glucose, such that A can only bind to DNA when glucose is present. You make changes in the binding sites such that the protein cannot bind to these specific sites (indicated by a "in the table; aindicates that the protein can bind) and measure Smrtl 7 mRNA production in cells containing equal 8 amounts of A and B proteins. Your results are summarized in the Table. Lab section Smrti transcription start site production? ) If the top strand of the DNA in the Figure is written in a 5 to 3 orientation, is the top or the bottom strand the template for transcription? (2 points) ) How does the binding of protein A affect gene expression? (3 points) ii) How does the binding of protein B affect gene expression? (3 points) ii In experiment number 1 which protein is bound to the Smril promoter? (3 points) Whi hpExplanation / Answer
Answer i): If the top strand is in 5' to 3' orientation than the bottom strand will acts as the template strand for transcription process because polymerization always takes place in 5'to3' orientation, hence it uses 3'to5' orientation strand as template (bottom strand).
Answer i: Protein A binds at binding sites when there is glucose present, the protein A is bound at A site on the promoter and does not allow the binding of RNA polymerase and inhibit the transcription or inhibit the gene expression. So the protein is a kind of repressor protein.
Answer ii: Protein B acts as activator protein as binding of this protein will allow the gene expression if it does not able to bind does not allow the gene expression and the binding does not affect by presence or absence of glucose.
Answer iii: In experiment1 the protein B binds at promoter and allow the transcription or gene expression, Protein A binds only in presence of glucose.
Answer iv: The protein A binds tightly in presence of glucose, it is clearly demonstrated in experiment 2 in which in presence of glucose the protein A binds and stop the gene expression even than the site B is also open.
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