Question

RNA polymerase which is on the promoter, moves to the structural genes to transcribe them. However, it happens when

• A. RNA polymerase shifts first to regulator gene.
• B. Inducer binds to structural genes.
• C. There is repressor on the operator.
• D. There is no repressor on the operator.

Answer 1

Answer: (D)

There is no repressor on the operator.

The promoter is a DNA segment that serves to initiate transcription of a particular gene. They are present upstream near the transcription start sites of genes. Regulator gene regulates the expression of structural genes by its protein product that is mostly transcription factors, also termed as the repressor. The operator is a DNA sequence present between the promoter region and the first coding gene. This operator region serves as a repressor protein binding site. The repressor binds to operator region which is located just upstream the binding site of the RNA polymerase and hence, prevent the binding and transcription; this makes option C incorrect. Regulator gene serves to regulate the expression of structural genes via repressor; it does not provide the binding site for RNA polymerase; option A is wrong. The inducer is a molecule that binds to repressor to prevent its binding to operator region and thereby, facilitates gene expression; option B is incorrect.