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    Analyzing Mutant Strains

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    1. Researchers have identified an E.coli strain having constitutive expression of camp. What would be the effect on lac operon expression in the following media? What if this mutant also contained an O^- mutation?
    a. Glucose
    b. Lactose
    c. Glucose + Lactose

    2. A mutant strain of E.coli has constitutive expression of the trp operon. How could this mutant phenotype result?

    3. A mutant strain of E.coli expresses trp operon mRNA but still cannot synthesize trypophan. How could this mutant phenotype result?

    4. Given the following data, what is the genotype of mutant X?

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    Solution Preview

    1. The theory behind the lac operon function does not really take in account the expression of cAMP. I don't think this information is needed for this problem. However, it's important to understand how the lac operon is structured, and why beta-galactosidase is produced when lactose is present, and production stopped when there is no more lactose left.

    The lac operon produced three genes, one of them being beta-galactosidase, which breaks down lactose into galactose and glucose. When lactose is present, beta-galactosidase is produced to break down lactose, so the lac operon is "activated". If you have media that only has glucose, beta-galactosidase doesn't need to be produced, since there is no lactose to be broken down. However, in the case where both lactose and glucose are present, it's the presence of lactose ...

    Solution Summary

    This solution explains in 542 words various results on phenotype from mutations, including how the lac and trp operons function, mRNA transcription and translation, and repressor and activation functions.