Molecular Genetics of Prokaryotes Problem Set

Problem 3: Phenotype of lac Z E. coli cells


An E. coli strain is lac Z. The structural gene for ß-galactosidase is encoded at the lac Z locus. How would you describe the regulation of lactose metabolism in these cells?

A. normal regulation of lactose metabolism.
B. constitutive expression of lac Z.
C. inability to synthesize the lac Z+ gene product, ß-galactosidase.
Cells mutated in the structural gene lac Z which encodes the enzyme ß-galactosidase cannot synthesize the enzyme.
D. lac Z gene is inducible, but unable to be repressed by high glucose.
E. no synthesis of the lac I gene product, the lac repressor.

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Updated: July 15, 1999
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