Question

The trp repressor binds to the operator region of DNA as a dimer (two repressor protein subunits bound together as a unit).You isolate a new mutant E.coli strain that you call Rnovel. In this strain, the repressor protein cannot attach to DNA (it cannot bind trpO+), but it can make dimers.In this strain, how is expression of the trp operon regulated?A. constitutiveB. inducibleC. repressibleD. noninducible

Answer 1

In the Rnovel strain, since the mutated trp repressor cannot bind to the DNA operator region, the trp operon would be constitutively expressed, continuously synthesizing tryptophan irrespective of its presence in the cell.

Step-by-step explanation:

In the mutant E.coli strain Rnovel you have mentioned, the trp repressor can form dimers but cannot attach to the DNA at the trpO+ operator region. Normally, the trp operon is a repressible operon, which means when tryptophan is present, it binds to the trp repressor, and the complex then binds to the operator to prevent transcription. However, since in the Rnovel strain the repressor cannot bind to the operator, the operon would be continuously active, and the genes for tryptophan synthesis would be expressed regardless of tryptophan presence. Thus, expression of the trp operon in this strain would be constitutive.

Answer 2

C. repressible

Step-by-step explanation:

The trp operon in bacteria is a repressible operon. The regulatory gene codes for repressor protein. In the presence of tryptophan, the repressor (inactive) binds with tryptophan and gets activated. This active repressor attaches with operator and prevent polymerase to bind and thus inhibiting transcription of genes in the operon.

The mutant strain cannot attach to operator (trpO+) but it can make dimers. As the operator is mutated so it prevent binding of repressor to operator. Thus, expression of the trp operon is repressible.