Lac Operon

• Production of Beta-galactosidase is controlled by lac operan along with two other proteins which are required for absorption and lactose metabolism
• Three genes are transcribed together in one mRNA, all three switched off when no lactose present
• P - Promoter region, RNA polymerase binds to start transcrption
• P - Promoter region, RNA polymerase binds to start transcrption
• O - Operator region, where inhibitor/repressor protein binds
• Z, Y and *A* - Structural lac Genes, for beta-galactosidase (digests), lactose permease (enables lactose in cell) and *another*
• Also i (gene regulator/repressor gene) on another bacterial chromosome part that codes for a repressor protein; binds to operator region and inhibits transcription of z, y and a
• E.coli prefer to respire glucose as it is more efficient, therefore in glucose and lactose presence, beta-galactosidase transcription is inhibited
• E.coli prefer to respire glucose as it is more efficient, therefore in glucose and lactose presence, beta-galactosidase transcription is inhibited
• Negative Control: Occurs when lactose is present and glucose absent; lac Operon is switched on when lactose binds to repressor protein, preventing it from binding to the O region and inhibiting RNA polymerase binding to P region
• Positive Control: cAMP is regulatory substance that binds to proteins causing 3D shape change; binds to cyclic AMP receptor protein (CRP) in lac operon; exposing DNA binding site on CRP - binding of activated CRP and DNA helps RNA polymerase to bind to promoter region and start gene transcription; cAMP levels are only high enough to activate CRP in glucose absence
• Positive Control: cAMP is regulatory substance that binds to proteins causing 3D shape change; binds to cyclic AMP receptor protein (CRP) in lac operon; exposing DNA binding site on CRP - binding of activated CRP and DNA helps RNA polymerase to bind to promoter region and start gene transcription; cAMP levels are only high enough to activate CRP in glucose absence