Regulation of Gene Expression

AP Biology· difficulty 3/5

In the lac operon, the actual molecule that binds and inactivates the LacI repressor is

A
$Galactose (a product of lactose breakdown)$
B
$Allolactose (an isomer of lactose)$
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C
$Glucose (a hydrolysis product of lactose)$
D
$Cyclic AMP (a low-glucose messenger)$

Explanation

A small fraction of intracellular lactose is converted to allolactose, which binds LacI and prevents it from binding the operator.

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