Page 56 - Cell biology PDG 2024

But if the repressor is removed from the operator, the RNA polymerase
will start transcribing the genes. How is the repressor removed?

When lactose is present, it binds to the repressor, changing its
conformation so that it can no longer bind to the operator. Thus the RNA
polymerase can transcribe the genes of the lac operon

Since the binding of the lactose induces the expression of the genes in the
lac operon, therefor lactose is called an inducer

Note that the lac operon itself encodes proteins that break down lactose.
Lactose presence will turn on these genes but once the lactose is broken
down, the repressor will bind to the operator again and the lac genes are
no longer expressed. This allows the genes to be expressed only when
they are needed

Figure 23: Lac operon expression

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