An _____ operon is usually inactive, unless it is made to become active.

An _____ operon is usually inactive, unless it is made to become active.

• A. Constitutive
• B. Inducible
• C. Repressible
• D. Promoter-regulated

Answer: (B)

An inducible operon is kept off most of the time and only turned on when an inducer molecule is present. This setup lets the cell conserve resources until the specific stimulus is needed. Typically, a repressor binds to the operator to block transcription; when the inducer binds to the repressor, the repressor changes shape and releases the operator, allowing RNA polymerase to proceed with transcription. This explains why the operon is usually inactive but can be activated when required. In contrast, a constitutive operon is expressed continuously because there’s no repressor blocking transcription, a repressible operon is generally on and can be shut off by a corepressor, and promoter-regulated describes regulation at the promoter but isn’t the standard categorization for operons like this.

An inducible operon is kept off most of the time and only turned on when an inducer molecule is present. This setup lets the cell conserve resources until the specific stimulus is needed. Typically, a repressor binds to the operator to block transcription; when the inducer binds to the repressor, the repressor changes shape and releases the operator, allowing RNA polymerase to proceed with transcription. This explains why the operon is usually inactive but can be activated when required. In contrast, a constitutive operon is expressed continuously because there’s no repressor blocking transcription, a repressible operon is generally on and can be shut off by a corepressor, and promoter-regulated describes regulation at the promoter but isn’t the standard categorization for operons like this.