Question

Lacl' is a mutant lac repressor protein that cannot bind to the operator.

Predict the phenotype of the lacl mutant.
a) The lac genes would be expressed efficiently only in the absence of lactose.
b) The lac genes would be expressed continuously.
c) The lac genes would never be expressed efficiently.
d) The lac genes would be expressed efficiently only in the presence of lactose

Answer 1

A lacI- mutant with a repressor that cannot bind to the operator results in the continuous expression of the lac genes, showing how gene regulation conserves vital resources like energy and materials. The correct option is b) The lac genes would be expressed continuously.

Step-by-step explanation:

The phenotype of a lacI- mutant, which produces a repressor protein that cannot bind to the operator, would lead to the lac genes being expressed continuously (option b). This is because the normal function of the lac repressor is to bind to the operator region of the lac operon, which blocks transcription by RNA polymerase when lactose is absent.

However, with the mutant lacI- repressor being unable to bind to the operator, RNA polymerase is no longer impeded and the lac genes are transcribed irrespective of lactose presence, leading to the constant expression of genes encoding enzymes for lactose metabolism.

This situation indicates the importance of gene regulation. Typically, genes are expressed only when needed to conserve energy and materials, as synthesizing proteins is metabolically expensive. The correct option is b) The lac genes would be expressed continuously.