When lactose is present, which enzyme binds to the promoter to Initiate transcription?

When lactose is present, which enzyme binds to the promoter to Initiate transcription?

• A. RNA polymerase
• B. Ribosome
• C. DNA ligase
• D. Topoisomerase

Answer: (A)

Transcription initiation is carried out by RNA polymerase. In bacteria, the RNA polymerase holoenzyme recognizes promoter sequences near the lac operon and binds there to start synthesizing RNA. When lactose is present, allolactose binds the lac repressor and removes it from the operator, freeing access to the promoter. With the promoter accessible, RNA polymerase can bind and begin transcription of the lac operon genes. The other enzymes do different jobs: the ribosome translates mRNA into protein, DNA ligase seals nicks in DNA, and topoisomerase relieves DNA supercoiling during unwinding.

Transcription initiation is carried out by RNA polymerase. In bacteria, the RNA polymerase holoenzyme recognizes promoter sequences near the lac operon and binds there to start synthesizing RNA. When lactose is present, allolactose binds the lac repressor and removes it from the operator, freeing access to the promoter. With the promoter accessible, RNA polymerase can bind and begin transcription of the lac operon genes. The other enzymes do different jobs: the ribosome translates mRNA into protein, DNA ligase seals nicks in DNA, and topoisomerase relieves DNA supercoiling during unwinding.