OPERON CONCEPT

• When E.coli cultured in a medium devoid of lactose the enzymes for lactose breakdown are not required.

• So the three structural genes are not expressed.

• In such a case the lac operon remains SWITCHED off or repressed.

• Under such a CONDITION the repressor protein coded by regulator gene ( i gene) is produced.

• The regulator gene is a gene which suppress the activity of structural genes.

• The repressor protein bind to the operator and blocks RNA polymerase movement.

• The operator gene thus directly control the structural gene as a result structural genes donot synthesis the mRNA and thus the enzymes are not synthesised this is called repression.

• When E.coli is cultured in medium containing lactose, E.coli needs enzymes for the breakdown of lactose, so the lac operon is switched on or derepressed.

• Under such a condition the lactose enters the E.coli and it GET modified into an inducer substance and binds with the repressor protein thus repressor protein structure is modified.

• Repressor cannot bind to the operator gene. Therefore the operator gene is free it induces the RNA polymerase to bind with PROMOTER gene.