In an operon model, regulator gene function as
A. Repressor
B. Regulator
C. Inhibitor
D. All of the above

Hint:-Operon, a genetic regulatory mechanism found in bacteria and their viruses, in which DNA is clustered with genes coding functionally similar proteins. This function enables organised regulation of protein synthesis in response to the cell 's needs. The operon enables the cell to conserve energy by providing the means to produce proteins only when and where they are needed.

Complete Answer:-A typical operon consists of a group of structural genes that code for a metabolic pathway involving enzymes. These genes are contiguously located on a DNA stretch and are under one promoter 's control. Different regulatory elements that react to environmental signals regulate the promoter. A regulator protein that binds to the operator region, which is another short segment of DNA located between the promoter and the structural genes, performs a typical method of regulation.
Regulator genes also code for repressor proteins in prokaryotes. Repressor proteins bind to operators or promoters, preventing the transcription of RNA polymerase by RNA. Typically, they are continuously expressed so that the cell still has a supply of repressor molecules on hand. Inducers alter the shape of repressor proteins or otherwise become unable to bind DNA, enabling transcription to proceed with RNA polymerase.
The Operon model involves a gene cluster that is under the influence of a single promoter. It consists of the structural genes of an operator, promoter, regulator and. As it produces a repressor protein that binds to the operator and thus inhibits the transcription of structural genes, the regulator gene acts as a repressor. It functions as a regulator as it guides structural gene transcription. The regulator gene product is an inhibitor that keeps the operon model shut off.

Hence, the correct answer is (d) All of the above.

Note:- Based on the environmental conditions that surround the cell, regulatory genes may also be identified as positive or negative regulators. Positive regulators are regulatory elements that permit the binding of RNA polymerase to the promoter region, enabling the occurrence of transcription. Negative regulators are regulatory elements that inhibit the binding to the promoter region of the RNA polymerase, thus repressing transcription.