What is the primary function of the first gene encoded by the Lac operon?

The primary function of the first gene encoded by the Lac operon, which is the gene lacZ, is to break down lactose. This gene encodes the enzyme β-galactosidase, which catalyzes the hydrolysis of lactose into glucose and galactose. The presence of lactose in the environment acts as an inducer for the Lac operon, leading to the expression of this gene, which allows the organism to utilize lactose as an energy source.

In the context of the regulation of the Lac operon, while other genes may be involved in regulating gene expression and responding to the availability of lactose (such as lacI, which codes for the repressor protein), the primary role of lacZ is directly tied to the metabolism of lactose itself. This makes option B the correct answer.

Other options involve different aspects of lactose metabolism and gene regulation but do not focus specifically on the primary biochemical function of the lacZ gene within the operon. For example, the synthesis of glucose (option A) occurs as a consequence of β-galactosidase activity but is not the primary function of the gene itself. The regulation of gene expression (option C) is related to the overall operon control but does not