Explain how the actions of the lac operon are different from the trp operon.
What will be an ideal response?
Answers may vary. The trp operon is a repressible operon. Repressible operons exist in the "on" rather than the "off" condition. In this system, the regulator codes for a repressor that is ordinarily not able to attach to the operator. Therefore, RNA polymerase is able to bind to the promoter and the structural genes of the operon are ordinarily expressed. When tryptophan is present, it binds to the repressor, changing its shape and allowing the repressor to bind to the operator. The structural genes are not expressed. Tryptophan is the corepressor. The lac operon is an inducible operon which is normally in the "off" rather than "on" condition. Lactose is the "inducer" of the operon. In this system, the regulator codes for a lac operon repressor that normally attaches to the operator and prevents transcription. When lactose is present, lactose binds to the repressor which changes the repressor's shape. The repressor is unable to bind to the promoter and RNA polymerase is better able to bind to the promoter. Transcription occurs.
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