in this video we'll look at how the Lac operon functions in eoli this is the Lac operon here you can see the three structural genes Lac Z Lac Y and Lac a Lac Z encodes the protein beta galactosidase Lac y encodes the enzyme permease and Lac a encodes the protein transacetylase all three of these proteins work together to help the cell bring in and break down lactose when it's available in the environment lactose is a sugar that the cell can use for energy and growth so these genes all share a promoter and an operator further Upstream of the Lac operon you see the regulatory Gene Lac ey which encodes an active repressor the cell wants to be able to break lactose down when it's present so expression of these genes is necessary when lactose is present in the environment when lactose is not present it would be a waste of the cell's energy and resources to continue to make these proteins so transcription of these structural genes will be limited so how does the cell alter structural gene expression when lactose is absent from the environment the Lac eye repressor is active it binds to the operator and prevents RNA polymerase from binding to the promoter this limits transcription of the lack genes in this state the operon is said to be repressed when lactose is present in the cell the low concentration of metabolizing proteins that are always available start to convert lactose into Alo lactose this Alo lactose acts as an inducer binding to the Lac ey repressor making it inactive the repressor becomes inactive because The Binding of alol lactose causes its DNA binding domain to change shape so it's unable to attach to the DNA operator in this state the repressor cannot block The Binding of RNA polymerase to the promoter and therefore transcription of the structural genes can occur this means that the lack proteins are produced and the cell is able to break down lactose at a higher rate in this state the operon is said to be induced by the presence of lactose the Lac operon is said to be inducible because lactose must be present for the structural genes of the operon to be expressed that's the Lac operon when lactose is present the repressor is inactive and the genes that encode the proteins that help break down lactose are expressed when lactose is absent the repressor is active and the cell limits production of those lactose metabolizing proteins as a way to save energy and resources if you'd like to delve deeper into the Lac operon check out out my Advanced La operon video if you want to learn about another operon check out my video on the trip operon