hey everyone quick like a mr. basics here so let's talk about the lac operon the lac operon is the best studied model for understanding the regulation of gene expression the genomic DNA of bacteria has many genes genes matter process of transcription and translation forms a protein both transcription and translation are highly energy intensive and zhilie those genes that are required for homeostasis are continuously expressed this type of expression is known as constitutive expression most of the genes are controlled by the extracellular signals which are usually molecules in the growth medium the signals that positively regulate the gene expression are called activators while the signals that negatively regulate gene expression are called repressors both activator and repressor are the DNA binding proteins that regulate the gene expression the DNA sequence at which the repressor binds is called an operator while the DNA sequence at which the activator binds is called an activator binding site now let's talk about the lac operon an operon is a functional unit of DNA containing cluster of genes under a single promoter the lac operon has three genes like Zi like Y and lack a the like C gene encodes beta galactosidase enzyme this breaks lactose into glucose and galactose the lac y gene encodes lactose permease enzyme this enzyme transports lactose inside the cell the like a gene encodes Tioga lactose ID trans acetylase enzyme and it helps in the removal of toxic tile gallic besides which are also transported by the leg why the lack I and cause a repressor that binds the operator and represses the lac operon let's see how the lac operon functions in absence of lactose the operator is occupied by lac repressor this ultimately shuts down the lac operon genes basal level transcription now sometimes even in absence of lactose the repressor may fall off from the operator allowing the transcription of lac genes this occurs because the binding of repressor with the operator is not permanent because of basal level transcription there is always some amount of lactose permease beta galactosidase and Tioga lactose i trans acetyl is enzyme present in the cell when lactose is present lactose enters the cell with the help of lactose permease remember lactose permease is present because of the basal level transcription of the lac genes lactose that enters the cell binds with the repressor and releases the repressor from the operator as the operator is free the RNA polymerase can now bind the promoter and initiate the transcription of lac genes now as lac genes are continuously transcribed more amount of lactose permease beta galactosidase and thigh galactose i trans acetylase enzymes are formed the lactose permease further allows more amount of lactose to enter the cell the lactose that enters the cell is hydrolyzed to glucose and galactose by beta galactosidase enzyme glucose and galactose are used as an energy source the role of CA p protein in lac operon CIP stands for catabolic activator protein c AP binds c mb hence it is also known as c and be receptor protein when the glucose levels in the cell decreases the level of cyclic a and B in the cell increases the camb binds CA B protein and activates it the CA MP CA B complex then binds to the CFP site and interacts with the c-terminal domain of the alpha subunit of RNA polymerase enzyme this increases the rate of transcription of lac genes [Music]