Gene regulation

Operon

A group of related bacterial genes controlled together by the same regulatory system

Like a light switch controlling multiple lights in one room

Promoter

Where RNA polymerase binds to begin transcription

Operator

DNA switch where a repressor can bind

Structural genes

Genes that code for the proteins or enzymes needed

What binds to the operator?

Repressor

What binds to the promoter?

RNa polymerase

Tryptophan operon (trp)

Helps make tryptophan, an amino acid

Repressible

On when trp is low

What happens when TRP is low?

The repressor is inactive, so RNA polymerase can transcribe the genes needed to make TRP

What happens when TRP is high?

Tryptophan binds to and activates the repressor. The repressor binds the operator, shutting transcription off.

Corepressor

Tryptophan acts as the corepressor because it activates the repressor

Lac operon

Helps break down bacteria and use lactose

Inducible

On when lactose is present

Repressor becomes active when lactose is present

What happens when lactose is absent?

The repressor is active and binds the operator, blocking transcription of the lactose-using genes

What happens when lactose is present?

The inducer inactivates the repressor. The repressor releases the operator, allowing transcription of the genes needed to use lactose