Question

In operon model, RNA polymerase binds to

• A. Promoter
• B. Structural gene
• C. Regulator
• D. Operator

Answer 1

The correct option is A Promoter

Operon
Operon is a cluster of genes which have a common promoter and are transcribed as a single polycistronic mRNA. Examples of operon include lac operon, trp operon, ara operon, his operon, val operon etc.
Structural gene
Structural genes are the DNA sequences in the operon which codes for proteins involved in a metabolic pathway.
The lac operon has three structural genes like lac z, lac y and lac a.
Promoter
Promoter is the site of initial binding of RNA polymerase. This then progresses to transcribe the downstream structural genes and produce mRNA.
Regulator gene
Regulator gene codes for the protein that regulates the process of transcription. In lac operon, lac i gene encodes a repressor that binds to the operator. Since the promoter and operator have overlapping sequences, the action of the repressor prevents the binding of RNA polymerase to the promoter and thus affects transcription.
Operator
Operator is a genetic sequence that lies adjacent downstream to the promoter region of DNA and regulates the synthesis of RNA from the downstream structural genes.
Final answer
(B) Promoter