Q) Explain the control of the lac operon by lactose
Main points | |
Key idea: | Role of repressor (during absence of lactose) – lac operon OFF |
· Lactose absent (in nutrient medium) : operator site bound by repressor mol which prevents binding of RNA polymerase to promoter · lac operon is switched off, struc genes not transcribed | |
Key idea: | Role of the lactose inducer – lac operon ON |
· Lactose present : some lactose transported into cells by low level of lactose permease present at surface of bacterial cells · lac operon switched on, struc genes transcribed | |
Key idea: | Mechanism of action |
· Lactose converted to allolactose by low level of β-galactosidase present · Allolactose inducer binds to repressor mol, changes its specific conformation · Repressor unable to bind to the operator site · RNA polymerase can bind to promoter, transcribe genes, results syn of (inducible) enzymes (i.e. β-galactosidase, lactose permease, lactose transacetylase) | |
Comments: (i) Visualize the answer with the aid of labelled diagram + animation (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) lac operon is an inducible system which can be activated by an inducer (i.e. allolactose) | |
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