The trp operon is said to be:

Moderate

A

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

Constitutively expressed and is never under negative regulation
C

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

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 .

Solution

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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