Tryptophan synthesis can be controlled by a process called attenuation in which the levels of tryptophan in the cell control translation by
A)the binding of the RNA polymerase to the genome.
B)the alteration of the repressor protein.
C)the folding of mRNA into hairpin loops.
D)genes rich in codons for tryptophan.

Question

Quizplus · Accepted Answer

Attenuation is a regulatory mechanism that controls the expression of the tryptophan operon in bacteria. It works by monitoring the levels of tryptophan in the cell and regulating the transcription of the operon accordingly. When tryptophan is abundant, the ribosome translating the mRNA quickly moves through the leader sequence, allowing stem-loop 3 and 4 to form, which terminates transcription prematurely. When tryptophan levels are low, ribosomes bind to the leader sequence and stall at codons that code for tryptophan, and instead stem-loop 2 and 3 form that compete with stem-loop 3 and 4 for formation. This choice results in attenuation and allows the mRNA to be fully transcribed, and synthesis of tryptophan to occur.

Tryptophan Synthesis Can Be Controlled by a Process Called Attenuation