THE STRUCTURAL GENES CONTROLLED BY THE LAC OPERON

The lac operon is a set of genes that are controlled by the Lac repressor protein in Escherichia coli (E. coli) and other bacteria. These genes are responsible for the breakdown of lactose (a sugar found in milk) and other sugars into glucose and galactose, which can then be used by the bacteria as a source of energy.

The structural genes controlled by the lac operon include:

1. lacZ: Encodes for β-galactosidase, an enzyme that breaks down lactose into glucose and galactose.
2. lacY: Encodes for β-galactoside permease, a protein that imports lactose into the bacterial cell.
3. lacA: Encodes for β-galactoside transacetylase, an enzyme that converts lactose into glucose and galactose.
4. lacB: Encodes for β-galactoside acetyltransferase, an enzyme that converts lactose into glucose and galactose.

The lac operon is regulated by the Lac repressor protein, which is a transcriptional repressor that binds to the lac operator sequence (a specific DNA sequence) and prevents the transcription of the structural genes into mRNA. When lactose is present, it binds to the Lac repressor protein and causes a conformational change that allows the transcription of the structural genes, resulting in the production of β-galactosidase and other enzymes necessary for lactose metabolism. This process is known as catabolic repression.

In summary, the lac operon is a set of genes that are controlled by the Lac repressor protein and are responsible for the breakdown of lactose and other sugars in E. coli. The structural genes controlled by the lac operon include β-galactosidase, β-galactoside permease, β-galactoside transacetylase, and β-galactoside acetyltransferase. The expression of these genes is regulated by the Lac repressor protein through a process of catabolic repression.