It is the action of the repressor that defines
the lac operon as an inducible system. In order to understand how the
system works, it is important to understand how the repressor functions. Clicking
on each of the thumbnail images will bring up a larger, labeled version of the
see the Flash movie for the following sequence of images,
The lac operon functions inside
a bacterial cell. This is a simplified bacterial cell.
An operon is a series of genes linked together on the
bacterial chromosome that are activated by a single promoter and produce
a single mRNA molecule.
Expression of the genes is turned off when a protein
called the repressor binds to the promoter (red) and operator (orange)
of the operon.
Lactose must be added to to activate the lac
operon. Here it is seen outside of the cellular membrane.
Some of the lactose enters the cell passively and binds
to the repressor molecule.
The repressor will only be removed when it is bound with