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.

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	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 expression.