Genes and products of the lac operon (E. coli) — z, y, and a In bacterial gene regulation, the lac operon contains three structural genes (z, y, and a). What do these genes encode, respectively?

Introduction:
The lac operon of Escherichia coli is a classic model of transcriptional regulation. It enables lactose utilization when glucose is scarce and lactose is available. Knowing the gene products of lacZ, lacY, and lacA is foundational.

Given Data / Assumptions:

• Structural genes: lacZ, lacY, lacA (z, y, a).
• Regulatory elements (lacI repressor, promoter, operator, CAP site) are distinct from the structural genes.
• Functional roles relate to lactose metabolism and transport.

Concept / Approach:

lacZ encodes β-galactosidase, which hydrolyzes lactose into glucose and galactose and can isomerize lactose analogs. lacY encodes lactose permease, a membrane symporter importing lactose. lacA encodes thiogalactoside transacetylase, which acetylates certain galactosides (a detox role).

Step-by-Step Solution:

Verification / Alternative check:

Genetic mapping and complementation tests historically defined z, y, and a functions; biochemical assays confirmed corresponding enzyme activities.

Why Other Options Are Wrong:

Options B and C omit one or two genes. Option D lists regulatory proteins, not the structural gene products. Option E substitutes unrelated enzymes and even the wrong sugar focus.

Common Pitfalls:

Confusing lactose permease with “galactose” permease, or thinking lacA is essential for lactose hydrolysis (it is accessory).

Final Answer:

β-galactosidase, lactose permease, and thiogalactoside transacetylase