Binding of the lac repressor protein to the lac operator is regulated allosterically. This means that the presence of a specific small molecule that binds to the lac repressor controls whether the repressor can bind to the lac operator, and therefore whether the operon is turned on or off. Can you sort the following conditions based on whether they are associated with the lac operon being turned ON or turned OFF? a. Allolactose is absent
b. Allolactose is present
c. RNA polymerase cannot transcribe the operan genes
d. The lac repressor protein cannot bind to the lac operator

a. OFF

b. ON

c. OFF

d. ON

Explanation:

Allosteric regulation is a process by which a particular molecule activates or inhibits an enzyme, by binding to a site different from the active site of the enzyme. Allolactose is a disaccharide that binds to the allosteric site of the lac repressor protein, triggering a conformational change in the protein that prevents the binding of this repressor to DNA. Moreover, RNA polymerase (RNA pol) is an enzyme required for the process of transcription, and therefore when this enzyme cannot bind to operon genes the lac operon is being turned OFF.  Finally, the lac operator is a nucleotide sequence where RNA pol binds, and the lac repressor binds to the lac operator in order to block the transcription of the lac operon.

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