If a cell is actually to exist and function effectively and efficiently it Must Be able to control and regulate the way that the cell expresses the genetic information That is found inside dna molecules Now what that basically means is the cell Must Be able to control the process of transcription it Must Be able to turn on transcription when we need to synthesize proteins and turn transcription those prote and this process is as gene expr and gene regulation now prokaryotic cells such as bacterial cells can regulate gene expression by using special types of molecules special types of proteins known as dna binding proteins and dna binding proteins Used by prokaryotes come two categories We have repressors and we have activators so during the process of transcription when we transcribe the dna into rna the activators can basically activate transcription while the repressors can Block the process of transcription and ultimately Block the synthesis of proteins that correspond to those Uh genes now our activators and PR protein molecules can themselves be controlled aleric by other molecules as We see in Just A Moment so When We're discussing prokaryotic gene regulation and expression basically The Model that describes the regulation of genes in prokaryotic organisms is known as the operon Model and What the operon is It's basically unit or a segment of dna that contains two important sections it contains the regulatory section as well as the coding section Now what exactly is the regulatory section and What Is Our coding section well to see What That is Let's take a look at the following diagram So this is basically our operon So this operon consist of the regular anding se now the regulatory section itself consists of two important control sides We have the promoter side as well as the operator side and We see What the function of those ses is in Just A Moment and our coding section actually consists of sequence of dna that code for certain types of polypeptides for certain types of proteins So this is our opron it consists of our control ses and it also consists of the structural genes now any given unit any given operon itself also is found next to a regulatory gene and the regulatory gene basically consists of the sequence of dna that codes for the repressor or Activator so every single operon next to the opron contains the regulatory gene that codes for either the repressor or the Activator that is involved within that oper um within that operon now to Gain more intuition and understanding to what the operon is and how it actually works Let's take a look at One particular example of the lack of a Of An opron known as the lack opron which stands for the la to operon This is the operon that is Used by certain type of prokaryotic Cell known as Ecoli so prokaryotic cells basically control the genes by using the change in concentration of certain types of biological molecules so prokaryotic cells have genes that respond to changes in concentration of certain types of biological molecules such as Glucose When Glucose concentration is high the Glucose can basically or the cell can metabol the Glucose and use the ATP produced by the process of glycolysis to power the different types of processes that take place within our Cell However What happens when the Glucose concentration is low When the Glucose concentration is low the cell must actually some other type of biological molecule and one other Common type of biological molecule that the cell metabol is lactose so lactose is a sugar molecule It's a disac that consists of two individual Sugar monomers so our lactose consist Of A Glucose as well as a galactose now the enzyme that actually catalyze is the breakdown of lactose into Glucose is known as beta galactosidase and beta galactosidase is basically controlled so the synthesis of the protein the enzyme beta galactosidase is controlled by a special type of opron found on the dna of the prokaryotic cell known as the la opron so Let's take a look at the la opron the la opron is is basically this section here so the la opron consists of two sections We have the regulatory section Which is basically this section here and we have our coding section the coding section basically consists of three genes that each code for a specific type of Uh enzyme That is involved in the breakd of lactose So this reg own by region number six contains the gene for the beta galas while these other genes are genes that code for two other proteins two other enzymes involved in the breakdown of lactose into Glucose And galactose now What about this section basically this section is the regulatory section it consists of our control ses now the la opron actually consist of of three sides We have our operator side We have the promoter side and we also have another type of side known as the cap side and we discuss what that means in Just A Moment and to the left of our cap side of site number three We have the gene that codes for the repressor protein and we also have the promoter of our gene that codes for the repressed protein so Let's discuss once again What happens when our Cell contains a high concentration of Glucose so When Glucose concentration is high rna polymerase will bind to the promoter region so region number one and when rna polymerase binds to our promoter region It will basically transcribe this dna molecule into An mrna molecule and then that Mr mrna molecule will be Used by the ribosome to basically synthesize the repressor protein and once a repressor protein is formed it will go on and bind to side number five so side number five is one of the control sides It's known as our operator region and once the repressor protein binds to the operator region using electric forces once it binds it basically will Block the process of transcription of these genes here so once form the repressive protein binds to the operator region and blocks the rna polymerase from transcribing the mrna molecule that codes for the beta galas as well as these other two types of genes now exactly does the cell need to Block the transcription of these mrna molecules that code for the proteins that Break Down lactose so This Is because inside the cell We have a high concentration of Glucose so We do not actually have to Break Down lactose Because we have the Glucose that we can use as our Energy source and so because the concentration of Glucose is high we do not need to synthesize the proteins the enzymes that are involved in the breakdown of lactose so once again this takes place because at high concentration of Glucose the cell does not need to use lactose as the Energy source because It has the Glucose in the first place and so the genes for our beta Gala as well as these other two genes the proteins involved in the breakdown of lactose are essentially turned off They are not expressed now what exactly happens when the Glucose concentration drops so When the Glucose concentration drops our cyclic amp or cyclic adenosine monophosphate concentration will increase and our Camp molecule will go on to bind to a special type of protein known as our catabolite Activator or cap and What the cap eventually does is it will bind to s number three but before that actually takes place when we have a low concentration of Glucose We're going to have a high concentration of lactose and some of that lactose will transform into another molecule known as allolactose and allolactose is basically that alic molecule that will go on and bind to our repressor protein and once it binds to the repressor protein shown in Red it will inactivate that repressor protein and that repress a protein that is bound to the operator will basically detach from the operator and once it detaches then our cap can basically bind to the and that will activate the promoter region this region that basically promotes the transcription of these genes and so When our repressor is inactivated and our cap bonds to our capside only then can the rna polymerase actually bind to the promoter and Begin the transcription of these genes so at a low concentration of our Glucose We want to be able to Break Down lactose to actually form the Glucose that we can use to break down and form our ATP molecules and so at low concentration of Glucose We want to Express the formation of our Uh beta galactosidase so that we can Use this beta galactosidase to actually Break Down our lactose molecule so One When the Glucose concentration is low and lactose concentration is lactose can transform into another disar known as allolactose which binds to the repressor protein alic and inactivates that repressor protein which then detaches from the operator side on our Aon on our now at the same exact time Because we have a low concentration of Glucose We're going to have a high concentration of cyclic adenosine monophosphate or Camp and then Camp will go on and bind to a molecule known as the catabolite activated protein or cap and the cap goes on to special side That is shown by s number three That is known as the capside so the capside is part of the regulatory section and once it binds to our capside that will activate our promoter and the rna polymerase will bind to our promoter and will Begin the synthesis of the mrna molecules that code for these proteins and then the proteins can synthesize and once We synthesize our proteins those proteins can be Used to metabol our lactose to form the Glucose that can then be used to form ATP via the pathway of glycolysis