The transcription of structural genes in an inducible operon occur (B) It starts when the pathway's substrate is present.
Inducible operon is the one which works only when the stimulus is received by an inducer, enhancer or a positive regulator. Inducible operon consists of one or more structural genes. The example of inducible operon is lac operon.
Substrate is a chemical substance upon which any enzyme acts. It is a starting material for any process to begin. In operons as well, substrate acts as an inducer for beginning the process of transcription. In lac operon, lactose itself acts as a substrate for the transcription of the m-RNA coding for enzyme β-galactosidase.
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