Question

select the correct answer. what is the determining factor for the transcription of structural genes of the trp operon? a. the quantity of trp repressor protein made by the regulatory gene trpr b. the ability of rna polymerase to bind to the promoter region c. the availability of tryptophan in the environment d. the location of a regulatory gene with reference to the other regions of the operon e. the activity of the other operons present in bacteria

Explanation:

The trp operon is a repressible operon. The key factor determining its transcription is the availability of tryptophan (trp) in the environment. When tryptophan is abundant, it acts as a corepressor, binding to the trp repressor protein. This complex then binds to the operator, preventing RNA polymerase from transcribing the structural genes. If tryptophan is scarce, the repressor is inactive, and transcription occurs.

• Option A: The quantity of trp repressor protein (made by trpR) is relatively constant and not the determining factor for transcription initiation of the structural genes (the repressor's activity, not its quantity, is regulated by tryptophan availability).
• Option B: RNA polymerase's ability to bind to the promoter is generally not the limiting factor here; the repressor - operator interaction (regulated by tryptophan) is the main control point.
• Option D: The location of the regulatory gene relative to other operon regions is not a determining factor for the transcription of the structural genes of the trp operon.
• Option E: The activity of other operons in bacteria is not related to the transcription of the trp operon's structural genes.

Answer:

C. the availability of tryptophan in the environment