Questions

The trp operon is said to be:

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Inducible operon because it is usually off but can be stimulated when lactose molecule interacts with a regulatory protein.

Constitutively expressed and is never under negative regulation

Lacking any regulatory gene and hence there is no formation of any repressor.

Repressible operon because its transcription is usually ON but can be inhibited when tryptophan binds allosterically to a regulatory protein which is inactive repressor and repressor- tryptophan complex can bind to operator to prevent transcription of structural genes .

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detailed solution

Correct option is D

The trp operon is said to be a repressible operon because its transcription is usually ON but can be inhibited (repressed) when a specific small molecule (in this case, tryptophan) binds allosterically to a regulatory protein.Lac operon is an inducible operon as it is usually off but can be stimulated (induced) when a specific small molecule interacts with a regulatory protein.Regulation of both the trp and lac operons involves both positive and negative control.The trp repressor is the protein product of a regulatory gene called trpR, which is located some distance from the trp operon and has its own promoter.

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