The tryptophan (trp)operon is turned on (i.e.gene expression occurs)when:
A)there is a great deal of tryptophan in the cell
B)there is a lack of tryptophan in the cell
C)the trp operon is always turned on
D)the trp operon is always turned off

Question

Quizplus · Accepted Answer

The trp operon is a repressible system, which means it is on by default but can be turned off when the end product, tryptophan, is in abundance in the cell. Therefore, the operon is turned on when there is a lack of tryptophan in the cell, and the genes in the operon are transcribed and translated to produce enzymes that synthesize tryptophan.

The Tryptophan (Trp)operon Is Turned on (I