Answer
Feedback, described in an earlier chapter when biochemistry was introduced, involves a product of some pathway regulating that pathway, usually negatively to turn the pathway down/off when enough product exists. That is what is shown in Fig. 18.2, and this chapter shows how this could be used beyond the mere allosteric regulation of enzymes by the product (a subject in an earlier chapter). Here you have seen that products can turn the production of enzymes and other important proteins up or down by complexing with the machinery of transcription.
Work Step by Step
This question asks you to explain the events of Fig. 18.2 in light of this chapter. Review earlier material on biochemistry as well as the regulation of biochemical operons (trp, lac) by feedback.
