Operon:
A group of genes that can switch on and off a gene.

Inducible operon:
An operon that isn’t working, because its REPRESSOR is active by default

Repressible operon:
An operon is working, and therefore the repressor is inactive by default

Inducible and Repressible Operons are each other OPPOSITES:
For Inducible the gene is OFF by default.
AND
For Repressible the gene is ON by default.

Negative Control of a Gene:
Inducible and Repressible
Because there is a repressor

Positive Control of a Gene:
Has an activator protein with makes it easy for the RNA polymerase to start.

  • Promoter = region where RNA polymerase binds
  • Operator = the “switch”
  • Terminator = Where transcription ENDS
  • Regulatory Gene = codes for a repressor or activator protein
    • Repressor = molecule that blocks transcription
    • Activator = molecule that promotes transcription

Inducible Operons:
There are certain genes on the operon, and if the operon starts EVERY gene on it turns on or off
The combination of the Promoter, Terminator, and Operator. By default it is Inactive.

Direction:
RNA Polymerase is moving from 3′ to 5′ AKA from left to right, so from the Promoter to the Terminator.

The Induce Molecule:
Binds to the Repressor Protein and changes the structure, which makes it INACTIVE, so it can’t bind to anything, and therefore transcription can START.

Repressible Operons:
There are certain genes on the operon, and if the operon starts EVERY gene on it turns on or off.
The combination of the Promoter, Terminator, and Operator. By default it is Active.

The Corepressor Molecule:
Binds to the Repressor Protein and changes the structure, which makes it ACTIVE, so it can bind to the Operator, and therefore transcription STOPS.

Positive Control of a Gene:
An Activator protein is created which helps the RNA Polymerase start transcription.

When the activator binds:
The RNA Polymerase can now RECOGNIZE that it is a promoter, if the activator isn’t there it won’t recognize it.