Final answer:
Repressors and activators are proteins that regulate gene expression in prokaryotic cells. Repressors prevent transcription of a gene in response to a stimulus, while activators increase transcription in response to a stimulus. Inducers are small molecules that 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 and activators are proteins produced in the cell. Both repressors and activators regulate gene expression by binding to specific DNA sites adjacent to the genes they control.
In general, activators bind to the promoter site, while repressors bind to operator regions. Repressors prevent transcription of a gene in response to an external stimulus, whereas activators increase the transcription of a gene in response to an external stimulus.
Inducers are small molecules that may be produced by the cell or that are in the cell's environment. Inducers either activate or repress transcription depending on the needs of the cell and the availability of substrate.