In the lac operon, the genes required to digest lactose are transcribed together because they are controlled by which DNA element?

In the lac operon, the genes required to digest lactose are transcribed together because they are controlled by which DNA element?

• A. Operator
• B. Promoter
• C. Enhancer
• D. Terminator

Answer: (B)

Transcription of the lac operon’s lactose-digesting genes happens from a single promoter, the DNA sequence where RNA polymerase binds to start transcription. Since all the structural genes lie downstream of this promoter, they are transcribed together as one polycistronic mRNA. The operator nearby is a regulatory site that binds the lac repressor to block transcription when lactose isn’t present, but it doesn’t initiate transcription itself. Enhancers aren’t the typical control elements in bacterial operons like this, and terminators signal where transcription ends rather than where it begins. So the promoter is the element that enables the genes to be transcribed together.

Transcription of the lac operon’s lactose-digesting genes happens from a single promoter, the DNA sequence where RNA polymerase binds to start transcription. Since all the structural genes lie downstream of this promoter, they are transcribed together as one polycistronic mRNA. The operator nearby is a regulatory site that binds the lac repressor to block transcription when lactose isn’t present, but it doesn’t initiate transcription itself. Enhancers aren’t the typical control elements in bacterial operons like this, and terminators signal where transcription ends rather than where it begins. So the promoter is the element that enables the genes to be transcribed together.