Question

A mutant E. coli strain is found that synthesizes B-galactosidase and permease but no B-galactoside-transacetylase in the presence of lactose (or allolactose). What mutation(s) can lead to this outcome? The lac operon is shown here as a guide. zones where proteins bind DNA: genes and regulatory sequences I lacl promoter operator lac Z l ac Y La repressor B-galactosidase B-galactoside transacetylase proteins Operator Laci promoter Lac Y Lac A Lacz

Answer 1

Answer - Lac A Explanation : The gene is Lac Z-Lac Y-Lac A Each Lac produce their corresponding mRNA. EACH mRNA produce corresponding enzyme. The different mutations possible in this gene are a) Inhibitor mutation Represented by letter This can be i minus or is I minus - always Inhibitor is off and gene products are always formed Is-Inhibitor is always activated and no gene product formed b) Z-minus mutation Here no beta galactosidase is formed c) Y- minus mutation Then Permease is not formed d) Oc mutation that is operator becomes constitutive and gene is always on e) P minus- that's promoter absent and gene is always off. In the given question both beta galactosidase and permease are formed and not beta galactoside transacetylase So it's not a) |- mutation where all are formed b) is - mutation where all are not formed c) Z- mutation, where beta galactosidase is not formed d) Y- mutation, No permease e) OC- mutation, where all are formed f) P- mutation None is formed Hence answer here is Lac A mutation Where Beta galactosidase and permease are formed and no Beta galactoside transacetylase. Note - function of Beta galactoside transacetylase is not known. Which is coded by Lac A.