Question

1.    The lac operon in E. coli comprises three structural genes, lac Z, lacY, and lacA....

1.    The lac operon in E. coli comprises three structural genes, lac Z, lacY, and lacA. It is regulated by both positive and negative mechanisms, involving binding of both a repressor protein and the catabolite activator protein (CAP). Transcription of the operon gives a polycistronic mRNA encoding the three enzymes. Under the following nutritional conditions, indicate whether or not the repressor and the CAP are bound by drawing them in on the appropriate regions of the operon. Indicate, as well, whether or not a messenger RNA is made and its relative quantity.

Use the following symbol:     - CAP;       - Repressor; ----------- mRNA

     a. When lactose and glucose are absent:

p i+ p+ o+ z+ y+ a+
DNA

      b. When lactose is present and glucose is absent:

p   i+ p+ o+ z+ y+ a+
DNA

      c. When both lactose and glucose are present:

p i+ p+ o+ z+ y+ a+
DNA
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Answer #1

CAP binds to the promoter region when glucose is absent.

Repressor bind to the operator region when lactose is absent.

Repressor mRNA : +i

Promoter: +p

Operatoe: o+

Beta-galactosidase : z+

Permease: y+

Transacetylase: a+

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