Scene 5: special scenario, in the lab FHigh glucose, some lactose, +IPTG (isopro

Question

Scene 5: special scenario, in the lab FHigh glucose, some lactose, +IPTG (isopropyl thiogalactoside- very efficie lac operon- even in the presence of glucose), +O cleavage by -galactosidase makes a yellow, soluble product) ent inducer NPG (orthnitropheylgalactoside m Promoter Operator lacZlacY lacA Scene 6: special scenario, in the lab High glucose, some lactose, +IPTG (isopropyl thiogalactoside-very efficient inducer of lac operon- even in the presence of glucose), +X-gal (5-bromo-4-chloro-3-indolyl- B-D- galactopyranoside)-cleavage by -galactosidase to makes a blue, insoluble product) Promoter Operator lacz lacY lacA

Explanation / Answer

scene 5) : In this case there is high glucose that means cAMP level is low that does not the catabolic activating protein to bind to tha CAP region ( i.e. positive regulatory site that facilitate the binding of RNA polymerase to the promoter when CAP proten binds to that region). also some lactose is present that means lactose converted to allolactose inside the cell, that binds to the lac repressor, alter its shape so it can not bind to DNA any more and turned on the operon. IPTG is also added that triggers the lac operon trancription. ONPG is added that will be cleaved by beta galactosidase i.e. encoded by lac z when operon is on. therefore in this case transcription of lac operon takes place at medium level that is confirmed by the amount of yellow colour product that is formed by the cleavage of ONPG.

scene 6): similarly as that happened in scene 5. the only difference is that in this case blue colour product is formed due to the cleavege of X- gal by beta galactosidase. also beta galactosidase converts lactose into glucose and galactose in both the case.

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