Polymerase binds the promoter, not the operator
- The idea
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- Why
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The idea
“The operator is where RNA polymerase binds, and the promoter is where the repressor sits.”
Operator sounds like the part that runs the genes, so it's easy to hand it polymerase's job. Both are short bits of DNA that a protein grabs.
The short version
The mistake: The operator is where RNA polymerase binds, and the promoter is where the repressor sits.
What's actually true: RNA polymerase binds the promoter to start transcription. A repressor binds the operator to block it.
- An operon is a cluster of bacterial genes transcribed together from one promoter. RNA polymerase binds the promoter to start making mRNA.
- The operator is a short DNA site next to the promoter. When a repressor protein binds it, polymerase can't transcribe the genes.
On the exam: Polymerase binds the promoter. The repressor binds the operator. A broken operator leaves the genes on.