Read the Lac Operon from Leak to Induction
The lac operon is inducible: a repressor blocks transcription until lactose-derived inducer binds it.
Lac Operon is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Allow inducer entry
A low basal expression of lac structural genes produces a small amount of permease. Lactose/allolactose can enter and bind the repressor, changing its shape so it releases the operator. This is negative regulation because the repressor normally blocks transcription.
Read the operon statements
The i gene constitutively produces repressor; lacZ encodes β-galactosidase, lacY permease and lacA transacetylase. A missense mutation in lacZ changes an amino acid and may alter enzyme activity. The inducer is not continuously synthesised regardless of conditions.
OlympIQ exam lens
- ✓Leakiness supplies basal permease.
- ✓Inducer binds repressor; operator becomes available.
- ✓Repressor control is negative regulation.
- ✓lacZ: β-galactosidase; lacY: permease.
The repressor is not the permease transporter; basal lacY expression solves the entry puzzle.
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