If the tryptophan repressor gene and its promoter,
were moved several hundred base pairs away from its normal location, what affect would you expect to see?

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BlackTom AI · Accepted Answer

First, consider the basics of bacterial operon regulation: the trp operon is controlled by a repressor protein (encoded by trpR) that interacts with the operator in a corepression-dependent manner. The key point is that the repressor is a diffusible product; as long as it is produced and functional, it can diffuse to the operon and regulate transcription, even if the trpR gene and its promoter are not adjacent to the operon.
Option 1: 'trp operon will be expressed continuously' would imply that the repressor is not functional or cannot bind the operator. If moving trpR and its promoter leaves a functional repressor being produced elsewhere, the operon would still be regulated by tryptophan levels, not simply expressed continuously. So this option is unlikely unless the repressor is entirely disrupted, which moving it a few hundred base pairs away from its normal location does not inherently cause.
Option 2: 'repressor will no longer bind to the operator' assumes a loss of binding capability. Distance between the regulator gene and the operon does not affect the biochemical ability of the repressor to bind DNA; binding is determined by the protein’s structure and the presence of corepressor (tryptophan). Therefore this is not a necessary consequence of relocation.
Option 3: 'trp operon will function normally' reflects the idea that the regulatory protein is diffusible and can regulate its target despite genomic distance, provided the repressor is produced correctly. This aligns with how prokaryotic regulation typically operates in vivo.
Option 4: 'repressor will no longer bind to the inducer' confuses the concept of inducer (in this system, the corepressor tryptophan enables binding of the repressor to the operator) with the notion of a separate inducer molecule; relocation does not create a new inducer binding defect unless the repressor’s structure is altered, which is not implied simply by distance.
Option 5: 'repressor will no longer be made' would require a disruption to the trpR gene itself or its promoter elements, not merely relocating them several hundred base pairs away. If the gene remains intact and properly transcribed elsewhere, the repressor can still be produced.
In summary, relocating the trpR gene and its promoter from their native neighborhood does not inherently eliminate repressor function or alter its ability to bind to the operator, nor does it create a new inducer defect; the core regulation depends on the presence and activity of the repressor protein, which, if functional, will regulate the operon as usual. Therefore, the most consistent outcome is that the trp operon will function normally.

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If the tryptophan repressor gene and its promoter, were moved several hundred base pairs away from its normal location, what affect would you expect to see?

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