what is lac operon? how it works with mechanism!

Operon:

Operon is the gene regulatory system of prokaryotes that contain operator ,promoter and all different corresponding genes among it. Normally eukaryotes contain one gene under a promoter but in case of prokarotes there can be more genes under one promoter thats why prokarotes are called polycistronic in nature.

Lac operon:

The Lac Operon is an example of an operon that is able to regulate itself depending on the environmental conditions it is subjected to.It codes for 3 genes: Beta-galactosidase, lactose permease and Thiogalactosidase transacetylase. These genes are involved in lactose metabolism pathway system. Below is the primary structure of a lac operon-


That mechanism is on the basis of presence of lactose in the environment. E.coli has the ability to grow in that media which contain lactose cause E.coli use lactose as their soul carbon source. we can consider lactose of any environment like laboratory culture or as we know our intestine contain a lot of E .coli bacterium.
So what is the functions of these 3 genes ?
Beta- galactosidase break down lactose which is a di-saccharides and turns it into two monosaccharides Glucose and galactose codes by gene lac Z

Lac permease This enzyme spans the cell membrane and brings lactose into the cell from the outside environment. The membrane is otherwise essentially impermeable to lactose. It is code for by the gene LacY
lac transacetylase is not still clear but they also helps to run the operation of lac operon codes by gene Lac A

Mechanism of lac operon:

Consider E.coli of our intestine and we had drunk milk that day so lacose is present in the intestinal environment , so the lac operon of the E.coli is so happy as they are going to take it. so system is turned on ! But suppose we didnt take any milk element that day and no lactose is present in the intestinal environment ! oh lac operon is now unhappy! If lactose is absent, the system is turned off; if lactose is present, the operon is switched on.

In the figure (a) you see lactose is absent in the environment as result lac I creating reppressor that inhibit the transcription process by making blocking to operator region of the gene. As repressor is binded with operator RNA polymerase will come but will not capable of binding with the promoter of the gene, as a result no transcription will happen.
Now suppose I drink a glass of milk as milk contain lactose what will happen?
Now the interesting thing gonna happen,when lactose shows upon in the environment their is a isomer formed called allolactose.Allolactose will go and bind with the repressor protein changing its from its active form to inactive form and will halt it from the operator.Now the lac operon is turned on, as a result operator is free from all hazards that mean the repressor (figure b) . so now RNA polymerase can come and bind with the promoter region and make transcription and further translation it will produce distinct protein!