In the absence of Lactose, what is expected to happen according to lac operon model ?

Question

Question

Structural genes transcribe for lactose permease
Repressor protein binds to the operator site
RNA polymerase interacts with DNA to initiate transcription
β-galactosidase, lactose permease and thiogalactoside transacetylase are synthesized

Answer 1

Concept-

Gene expression is the mechanism at the molecular level by which a gene can express itself in the phenotype of an organism.
The mechanism that stimulates the expression of certain genes and inhibits that of others is called the regulation of gene expression.
Francis Jacob and Monod proposed a mechanism called the operon model for the regulation of gene action in E.coli.
An operon is a part of genetic material that acts as a single regulated unit having one or more structural genes, a promoter gene, a regulator gene.
Operons are of two types- inducible and repressible.
The best-known operon is lac operon.

Explanation-

F1 Hemant 06-07-21 Savita D5

In the absence of lactose, the repressor protein binds to the operator region of the operon.
It prevents RNA polymerase from transcribing the operon.

Thereby option B is the correct answer.

Additional Information

In the presence of an inducer, such as lactose or allolactose, the repressor is inactivated by interaction with the inducer.
This allows RNA polymerase access to the promoter and transcription proceeds.
Essentially, regulation of lac operon can also be visualized as regulation of enzyme synthesis by its substrate.