Final answer:
Repressors are proteins that suppress transcription, activators increase transcription, and inducers can activate or repress transcription depending on the cell's needs.
Step-by-step explanation:
In prokaryotic cells, there are three types of regulatory molecules that can affect the expression of operons: repressors, activators, and inducers. Repressors are proteins that suppress transcription of a gene in response to an external stimulus, whereas activators are proteins that increase the transcription of a gene in response to an external stimulus. Finally, inducers are small molecules that either activate or repress transcription depending on the needs of the cell and the availability of substrate.