Final answer:
A repressor is a protein that suppresses gene transcription by binding to the operator, blocking RNA polymerase from transcribing genes within prokaryotic cells' operons.
Step-by-step explanation:
A repressor is a protein that influences the ability of RNA polymerase to transcribe a given gene. This protein functions in the regulation of gene expression in prokaryotic cells. Proteins such as repressors, activators, and inducers are key components in gene regulation, particularly within operon systems. Repressors bind to the operator, a specific DNA sequence within the regulatory region situated between the RNA polymerase binding site in the promoter and the first structural gene. This binding physically blocks the transcription process.
Contrastingly, activators assist RNA polymerase in binding to the promoter, thereby enhancing transcription. Inducers, on the other hand, are small molecules that can either increase or suppress transcription through their interaction with repressors or activators, based on cellular needs and substrate availability.