The trp operon in E. coli contains a 5' UTR sequence that is translated into a small polypeptide of 14 amino acids, which includes two tryptophans. If the two trp codons in the 5' UTR of the RNA are changed to serine codons and the resulting cells are starved for tryptophan but not for any other amino acid, what will be the effect of the mutant codons on the operation of the trp operon?
A) The trp repressor will be synthesized in greater amounts.
B) Expression of the trp structural genes will be less than with a normal trp operon.
C) Expression of the trp structural genes will be greater than with a normal trp operon.
D) The leader polypeptide will not be synthesized.
E) The expression of the operon will not be affected by these mutations.

Question

Quizplus · Accepted Answer

The trp operon is an inducible operon, meaning that its expression is turned on in the presence of tryptophan. The trp repressor is a protein that binds to the operator region of the trp operon and prevents transcription of the structural genes. The leader polypeptide is a small polypeptide that is translated from the 5F1F1F1S1F1F1F10 UTR of the RNA. The leader polypeptide binds to the trp repressor and prevents it from binding to the operator region, allowing transcription of the structural genes. If the two trp codons in the 5F1F1F1S1F1F1F10 UTR of the RNA are changed to serine codons, the leader polypeptide will not be synthesized. This will allow the trp repressor to bind to the operator region and prevent transcription of the structural genes. Therefore, expression of the trp structural genes will be less than with a normal trp operon.

The Trp Operon in E