Final answer:
The statement is true; a terminating 'hairpin' loop forms in the trp operon when tryptophan levels are high, binding the repressor to the operator and preventing transcription. This is a negative feedback regulation mechanism where the product of the pathway inhibits its own production to conserve cellular resources.
Step-by-step explanation:
The statement that the terminating "hairpin" loop occurs in the trp operon when sufficient tryptophan is present is true. In the mechanism of the trp operon, when tryptophan levels are high, tryptophan molecules bind to the trp repressor protein, which then binds to the trp operator, preventing RNA polymerase from transcribing the structural genes. This form of regulation ensures that when tryptophan is abundant, the cell does not waste resources producing enzymes for its synthesis. The presence of tryptophan effectively halts the transcription process through the formation of a terminator loop between regions 3 and 4 of the RNA being transcribed, which is often referred to as the "hairpin" loop.
When tryptophan is scarce, the operon mechanism is quite different. The repressor protein remains inactive and does not bind to the operator, allowing genes necessary for tryptophan synthesis to be transcribed. In this case, an antiterminator loop forms between regions 2 and 3, allowing transcription to continue and the cell to synthesize tryptophan.
Thus, the trp operon is a classic example of a negative feedback mechanism, whereby the product of the pathway, tryptophan, regulates its own synthesis by influencing the function of the trp operon through a system of regulatory loops.