Gene Switches

Change an inducer condition and watch access to a gene change.

Experimental Lac repressor dimer shown in violet secondary structure bound to cyan operator DNA.

Structural referencePDB 1EFA PDB 1LBG

Inducer condition

Lac repressor present

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Step 1 of 4

Set conditions

Lac repressor is present. No inducer is present. The coding sequence stays the same in every condition.

This is one regulatory relationship in a bacterial system. The full lac operon also responds to glucose. Molecules encounter partners through motion and binding; the arranged transitions here explain the relationship, not a directed search or measured kinetics.

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Quick reference

Regulating access

In the bacterial lac system, the Lac repressor binds operator DNA and reduces transcription of genes involved in lactose metabolism. Regulation changes how much a gene is expressed without requiring a change to its coding sequence.

An inducer changes binding

An inducer binds the repressor and shifts its conformational behaviour, reducing its affinity for operator DNA. The model uses an IPTG-like inducer as a controlled teaching input.

One part of regulation

The full lac system also responds to glucose through additional regulation. Here those conditions are held fixed, and basal transcription and binding fluctuations are omitted to make the repressor relationship visible.

Check your understanding Optional

An inducer increases expression in this model. What changed?

The repressor's interaction with operator DNA.Every codon was replaced with a stronger codon.The gene moved from DNA into a protein.

At the bench

Recognise promoters, regulatory elements and coding sequences when inspecting a construct.

Open Plasmid

Sources and model notes

Structure-based views of resolved experimental coordinates. Cutaways, category colours, camera choices and guided highlights are authored for teaching. Coordinates remain fixed; highlights are not experimental trajectories or simulation outputs.

RCSB PDB · Lac repressor study

Structures of repressor with operator DNA and inducer; the original study covers the binding mechanism.