Why do different kinds of control mechanisms exist?

Cells contain a diverse set of different mechanisms for controlling gene activation. In general, the type of mechanism controlling the synthesis of a gene product depends on the product's function. If a product is involved in an catabolic pathway then gene expression will be stimulated by initial substrates of the pathway and repressed by final products of the pathway. Initial substrate molecules can either inactivate repressor proteins or induce activator proteins. Final product molecules would activate repressor proteins. Using these types of control mechanisms the genes for the pathway molecules could be turned on when there is a lot of the substrate molecules and turned off when there is a lot of the of the final product. V

An active repressor protein:
A. is a structural protein.
B. binds to the DNA molecule and promotes transcription initiation.
C. binds to the DNA molecule and prevents transcription. binds to the RNA polymerase, preventing messenger RNA synthesis.
D. binds to an inducer to activate it.

A repressor is a DNA-or RNA-restricting protein that restrains the outflow of at least one qualities by authoritative to the operator or associated silencers.
A RNA-restricting repressor ties to the mRNA and forestalls interpretation of the mRNA into protein. This hindering of articulation is called repression.
Transcribing a gene, RNA polymerase ties to the DNA of the quality at an area called the promoter.
It contains acknowledgment locales for RNA polymerase or its aide proteins to tie to.
The DNA opens up in the advertiser district with the goal that RNA polymerase can start translation.
Interpretation factors are an exceptionally assorted group of proteins and by and large capacity in multi-subunit protein edifices.
They may tie legitimately to uncommon “promoter” locales of DNA, which lie upstream of the coding area in a quality, or straightforwardly to the RNA polymerase atom.