Tag: expression of gene

The gene that codes for any RNA/protein product which does not serve as regulatory protein is known as structural genes. The operator is a DNA sequence present between the promoter region and the first coding gene. The operator region serves as the repressor protein binding site. 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 in between the operator and structural gene. The regulatory gene regulates the expression of structural genes by its protein products that are mostly transcription factors. It is not the part of an operon, which means that it is present upstream or downstream the structural genes but not in between; the Regulatory gene is present upstream the operator gene. Thus, the correct answer option D.

In the operon model, the operator is the gene segment to which a repressor binds. This prevents the RNA polymerase from transcribing certain genes in the operon unit.

Lac repressor is part of the regulatory network of the lac operon. Lac repressor controls the production of three proteins produced from the gene and affecting the metabolism of lactose. This repressor molecule is a tetramer whose all the subunits are identical. This tetramer binds to a particular region in the bacterial DNA called the operator. This region is present next the three lactose metabolizing proteins. Binding of the repressor to operator causes the block in the production of protein. Otherwise, for three genes to transcribe the repressor protein binds to the lactose molecule and hence unable to bind to operator allows the genes to transcribe.