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BIOL 308 Final: Study_questions_6

5 Pages

Course Code
BIOL 308
Dragana Miskovic

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1. You have discovered base changes in the promoter region of the operon in a bacterial chromosome. Would you expect these changes to act in trans on another copy of the operon? Explain your reasoning. No, they would not act in trans on another copy of the operon because promoter regions only affect the dna that they are on. To act in trans means to be able to affect the expression of another molecule of dna, this would not be the case here. No gene product formed as result of promotor region. 2. What are cis elements? What are trans factors? Give an example from the Trp operon (or form the Araoperon). Cis elements can only act on the strand of dna that they are on (in TRP, the binding site for the aporepressor is a cis element). A trans factor is mobile and can interact with other strands of genes and affect their expression (tryptophan as a corepressor is an example of a trans factor). In Lara operon, AraO2 is a cis site which araC will bind to in order to block transcription from occurring. In lara operon, arabinose is a trans factor which can bind to arac protein, change its conformation so it binds to i1 and I2 3. Draw the diagram of the lac operon that illustrates negative control. 4. You have isolated a protein that binds to DNA in the region upstream of the promoter sequence of the gene of interest. If this is a positive regulator (activator) which would be true: A) Loss of function mutation in the gene encoding this DNA binding protein would cause constitutive expression B) Loss of function mutation in the gene encoding this DNA binding protein would result in lower or no expression. Explain your reasoning. It would lead to lower or no expression because a positive regulator involves stimulating transcription of downstream gene by increasing ability for rnap to bind with promotor region. Loss of this protein would reduce that stimulation of transcription thus lowerno expression. c 5. Discuss why are lac O mutants cisacting. Because the operator sequence on a gene only affects the expression on that strand. A repression is not able to bind to the operator on this strand as it is mutated thus expression is constitutive but it will not stop a repressor from bind to another gene with a functional repressor. Thus, cis acting, only on its own strand and expression. 6. Discuss why are lac I mutants transacting.
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