For the lac operon cycle to come full
circle, the system must once again be shut off. This occurs when the two proteins
studied earlier complete their functions and pave the way for the repressor
to return to its place on the chromosome. Clicking on each of the thumbnail
images will bring up a larger, labeled version of the described scene.
see the Flash movie for the following sequence of images,
As the concentration of lactose in the cell
drops, the lactose bound to the repressor are released.
The last of the lactose is then broken down by the ß-galactosidase.
Free of the lactose molecules, the repressor again binds
to the promoter and operator of the operon and effectively turns off gene