Which of the following statements is correct about the role of regulatory proteins in transcription in prokaryotes?

📌 Concept:
-Gene expression refers to the process by which the information in the genes is expressed in the form of a protein product.
-Regulation of gene expression may take place at various levels and may be controlled by metabolic, physiological, or environmental conditions.
-One of the regulation mechanisms is a transcriptional regulation system.
-In prokaryotes, we find polycistronic genes, which are mostly regulated at the transcription initiation site.
-In a transcription unit, the function of RNA polymerase is regulated by interactions with some regulatory proteins.
-This is known as an operon system, which can be either positively (by activators) or negatively controlled (by repressors). 
🔑Key Points: 
-An operon is a part of genetic material which acts as a single regulated unit having one or more structural genes.

✏️The lac operon consists of the following parts:

✏️Structural Gene – It consists of 3 genes:
-z – codes for β-galactosidase
-y – codes for permease
-a – codes for transacetylase
-Operator –
-It is present adjacent to the structural gene.
-It is the site for the binding of repressor proteins.
-Regulator –
-It comprises the i-gene, which codes for the repressor protein.
-The repressor protein is synthesized all the time constitutively.
-Promoter –
-It is the transcription initiation site where RNA polymerase binds.
-Inducer –
-It is the molecule that determines whether the repressor will bind to the operator or not.
-Hence, it regulates the operon.
-Example – Lactose in lac operon.
-Lac operon is regulated by a repressor and hence it is a negative regulation.

✅ Explanation:
-In the absence of lactose, the repressor protein binds at the operator site and prevents RNA polymerase to transcribe the structural genes.
-But in the presence of lactose, transcription of the genes takes place.
-The inducer binds to the repressor and inactivates it by forming the repressor-inducer complex.
-This complex prevents the repressor from binding with the operator.
-Thus, the RNA polymerase slides along the DNA without any hindrance, and thus, the genes get expressed.