As we’ve just learned, 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. In other words, a repressor keeps a gene “off.”
• Activators are proteins that increase the transcription of a gene in response to an external stimulus. In other words, an activator turns a gene “on.”
• Inducers are small molecules that either activate or repress transcription depending on the needs of the cell and the availability of substrate. Inducers basically help speed up or slow down “on” or “off” by binding to a repressor or activator. In other words: they don’t work alone.

In the interactive below, we will focus on the differences between regulatory molecules in gene expression:

Click here for a text-only version of the activity.