LAC Operon

The lac operon can be defined as an Operon, or group of genes with a single promoter. The genes present in the operon encodes the proteins that allows the bacteria to process the lactose as an energy source.


Gene regulation is often defined as any quiet alteration within the gene to offer rise to a special expression that could end in a change within the synthesized amino acid sequence. Gene expression is essentially the synthesis of the polypeptide chain encoded by a specific gene. Therefore, we will say that the expression of the gene is often quantified in terms of the quantity of protein synthesized by the genes.


Let’s study the regulation of organic phenomenon in prokaryotes with the instance of Lac Operon.

Regulation of Gene Expression

We can infer that the gene regulation can happen at various steps of an organic phenomenon which incorporates the following:

Replication level

Any error in copying the DNA may end in an altered expression.

Transcriptional level 

During transcription, any error within the polymerization may again cause a change in expression of the gene.

Post-transcriptional level

During the post-transcriptional modification i.e., RNA splicing, there could also be some changes.

Translational level

During translation, if there's a mistake within the attachment of mRNA to the RNA molecules, there may arise some changes. 


The regulation of the expression of the gene is often explained with the instance of an enzyme, say peroxidase in bacteria. This enzyme catalyzes the hydrolysis of hydrogen peroxide to water and oxygen. Now, if the bacteria are moved to a different environment where they fail to manufacture peroxide, the enzyme does not play its role. In such a situation, the bacteria will not synthesize the enzyme anymore. Thus, we will say that the environmental, metabolic, and physiological state regulates the expression of genes.

Gene Regulation in Prokaryotes

Gene regulation in prokaryotes is most extensively found at the initiation of transcription period. Thus, the organic phenomenon during transcription initiation is suffering from regulation. The regulation usually takes place within the expression of the RNA polymerase at the promoter site. This affects the accessory proteins which bind to the popular sites. These proteins can help the promoter site in two ways:

  • Positive regulation by activators

  • Negative regulation by repressors

In Operons, the operator is situated right next to the promoter where the regulator binds to regulate its entire functioning. 

Lac Operon

“Lac operon is an operon or a gaggle of genes with one promoter that encodes genes for the transport and metabolism of lactose in E.coli and other bacteria.”

Lac Operon Concept

Gene regulation in prokaryotes is often explained with the assistance of the Lac Operon model. Here the alteration in physiological and environmental conditions is often observed resulting in an alteration in expression in prokaryotes. It was observed by Jacob and Monod.

The lac operon consists of:

  • Regulatory gene i

 It helps to code for the repressor protein.

  • z gene

It is the key for beta-galactosidase which catalyzes the hydrolysis of lactose into glucose and galactose.

  • y gene

It is the key for permease which controls the lactose permeability inside the cell.

  • a gene

It is the key for transacetylase which helps the enzyme beta-galactosidase.

Hence, all these genes help in lactose metabolism. In the lac operon, lactose works as an inducer. If lactose is given in the medium for the bacteria, the regulatory gene is activated. The inducer will hold the repressor protein and render it inactive which allows transcription of the operon. Thus, the lac operon is negatively regulated during this case.


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FAQ (Frequently Asked Questions)

Define LAC Operon

Lac operon is an operon or a gaggle of genes with one promoter that encode genes for the transport and metabolism of lactose in E.coli and other bacteria.

2. What is the concept of LAC Operon?

Gene regulation in prokaryotes are often explained with the assistance of the Lac Operon model. Here the alteration in physiological and environmental conditions is often observed resulting in an alteration in expression in prokaryotes. It was observed by Jacob and Monod. The lac operon consists of:

Regulatory gene i – It codes for the repressor protein.

z gene – It codes for beta-galactosidase which catalyzes the hydrolysis of lactose into glucose and galactose.

y gene – It codes for permease which regulates the lactose permeability within the cell.

a gene – It codes for transacetylase which assists the enzyme beta-galactosidase.