Final answer:
Inducible operons are normally found in catabolic pathways where the presence of a substrate induces gene expression, and are not typically involved in anabolic pathways, which are often associated with repressible operons. The lac operon of E. coli is a well-known inducible operon that requires lactose as an inducer to activate transcription of the genes required for lactose metabolism.option c is the answer.
Step-by-step explanation:
The student question involves characteristics of inducible operons, which are systems found within prokaryotic cells, such as bacteria, that control gene expression. Among the options given, the characteristic that does NOT apply to inducible operons is C) they often involved in anabolic pathways. Inducible operons are typically associated with catabolic pathways, where the substrate's presence is necessary to induce the expression of the operon's genes. In contrast, anabolic pathways are often associated with repressible operons, where the end product of the pathway will inhibit its own synthesis when present in sufficient amounts, saving energy for the cell.
Inducible operons like the lac operon are a classic example wherein the presence of lactose triggers the operon to allow the cell to process lactose. This operon utilizes a repressor which, in the absence of lactose, will bind to the operator and prevent transcription. However, when lactose is present, it acts as an inducer by binding to the repressor and preventing it from blocking transcription, thereby allowing the operon to be active. In addition to lactose acting as an inducer, conditions such as a low glucose concentration can lead to the cAMP-CAP complex serving as a positive regulator to induce transcription of the lac operon.
The trp operon exemplifies a repressible operon as the presence of tryptophan will cause the operon to be repressed and prevent excessive synthesis of tryptophan.