Final answer:
In the lac operon, some of the nucleotides of the operator are also part of the promoter. A mutation in one of the structural genes such as lacZ, lacY, or lacA could impair lactose metabolism.
Step-by-step explanation:
In the lac operon, some of the nucleotides of the operator are also part of the promoter. This configuration allows for the precise regulation of gene expression in response to the presence or absence of lactose. When a repressor binds to the operator, transcription of the structural genes is inhibited. These structural genes, namely lacZ, lacY, and lacA, code for proteins necessary for lactose metabolism. A mutation in one of these genes could disrupt the production or function of the enzyme it encodes, potentially preventing the bacterium from effectively metabolizing lactose.