Final answer:
The lacZ gene in the lac operon codes for ß-galactosidase, which breaks down lactose into simpler sugars. Mutations in this gene can impair the ability of E. coli to metabolize lactose, affecting its survival in environments where lactose is the main nutrient source.
Step-by-step explanation:
The role of the first structural gene, lacZ, in the lac operon is to encode ß-galactosidase, which is an enzyme that breaks down lactose into galactose and glucose. This gene is part of a cluster including lacY and lacA, which code for lactose permease and transacetylase, respectively. Lactose permease facilitates the entry of lactose into the cell, while the function of transacetylase in lactose metabolism is not fully understood. The expression of the lac operon is under tight regulation, and control mechanisms ensure that the operon is expressed significantly only when lactose is present and glucose levels are low, making the lac operon a classic example of an inducible system in bacteria such as E. coli.
A mutation in any of the structural genes, including lacZ, can result in the loss or reduction of the associated enzyme's activity, which would impact the bacterium's ability to utilize lactose as a nutrient source.