Question

What is the sequence of structural genes by lac operon?
A. Lac A, Lac Y, Lac Z
B. Lac A, Lac Z, Lac Y
C. Lac Y, Lac Z, Lac A
D. Lac Z, Lac Y, Lac A

Answer 1

The operon is the group of genes that are placed side by side in a sequence and function in a coordinated manner. The lac operon is the operon system of lactose. Here lac refers to lactose. It is based on the inducible gene concept.

Complete answer:
The lac operon genes –
Regulator gene $\left( i \right)$ - It is also known as the inhibitor gene. It is the gene that codes for the repressor protein. It is synthesized all the time from the $i$-gene. Due to this, it is a constitutive gene that is always functional.
Promoter genes – It is the gene that possesses the site for the RNA polymerase attachment.
Operator gene – It is the gene that interacts with the protein molecule or the regulator molecule, which prevents the transcription of the structural genes.
Structural genes – Three types of structural genes are found in lac operon –
lac Z – The Z gene codes for the enzyme $\beta$-galactosidase. This enzyme is primarily responsible for the hydrolysis of the disaccharides, like lactose into their monomeric units, glucose, and galactose.
lac Y – The Y gene codes for the enzyme permease. This enzyme increases the permeability of the cell to the $\beta$-galactosidase.
lac A – The A gene codes for the enzyme transacetylase. This enzyme transfers the acetyl group to the $\beta$-galactosidase.
Hence, the correct answer is option (D).

Note: The lac operon is the operon system of lactose. Here lac refers to lactose. The lac operon consists of one regulatory or inhibitor gene, one promoter gene, one operator gene, and three structural genes. The structural gene is polycistronic here. It is regulated by the common promoter and regulatory gene.