IPTG (isopropylthiogalactoside) iscommonly used to induce proteinexpression in Lac operon-regulated gene inE. Coli, because IPTGa. is a repressor to Lac operon.O b. is an enhancer binding compound.O C.O d.unwinds DNA, leading to DNA duplication andtranscription.is a mimetic of allolactose, that binds to repressor,causing it release from the operator of the lacoperon, leading to transcription.

IPTG, also known as isopropyl d-1-thiogalactopyranoside, is a molecular biology tool. This substance is utilized to promote protein expression in situations where the lac operator controls the gene because it is a chemical mimic of allolactose, a lactose metabolite that causes transcription of the lac operon. Similar to allolactose, IPTG binds to the lac repressor and, in an allosteric manner, frees the tetrameric repressor from the lac operator, enabling transcription of genes in the lac operon, including the gene encoding beta-galactosidase, an enzyme that catalyzes the hydrolysis of β-galactosidase into monosaccharides. The Sulphur (S) atom, in contrast to allolactose, forms a chemical bond that the cell cannot hydrolyze, preventing the cell from metabolizing or decomposing the inducer. Consequently, its concentration is maintained in experiment. Since alternative transport channels are implicated, IPTG absorption by E. coli can occur without the involvement of lactose permease. When employed at high quantities (usually for protein induction), IPTG can enter cells without the help of lactose permease. At low concentrations, IPTG penetrates cells through lactose permease.The answer to given question is option d. Because it is the chemical mimic or lac repressor allolactose. And binds to to the repressor as that of allolactose and causes the release of repressor from the operator gene and also allows the gene to transcription. IPTG and X-gal are both utilized in blue-white screen. In cloning experiments, a blue-white screen makes it possible to distinguish recombinant plasmid-transformed colonies from non-transformed ones. The option a, is wrong. Because it is not a repressor to the lac operon gene. It is a chemical mimic of repressor allolactose. The option b is also wrong. Because it is not the enhancer it will bind to repressor protein which inhibit the transcription but that will not considered as enhancer. Enhancer will binds to gene and enhances the transcription. The option c is also wrong. Because IPTGs mechanism wont unwinds the DNA and leads to DNA replication and then transcription.