Why Transcription Needs To Be Regulated
- Every cell in an organism contains the same genome, but different cells express different genes.
- A muscle cell produces muscle proteins; a nerve cell produces neurotransmitters.
- This specificity is achieved by regulating transcription, controlling which genes are transcribed into mRNA.
- Proteins bind to specific DNA sequences to turn genes on or off.
Key DNA Sequences That Control Transcription
1. Promoters Are The Starting Point
Definition
Promoter
A promoter is a specific DNA sequence located near the start of a gene. It acts as a binding site for RNA polymerase and other proteins needed to initiate transcription.
- The promoter marks where transcription begins.
- RNA polymerase binds to the promoter to start transcribing the gene.
- A common promoter sequence in eukaryotes is the TATA box (TATAAA), which helps position RNA polymerase accurately.
The promoter is like a runway where RNA polymerase "lands" to begin the transcription process.
2. Enhancers Are Sequences That Increase Transcription
Definition
Enhancers
Enhancers are DNA sequences that increase the rate of transcription when activator proteins bind to them.
- Enhancers can be located far away from the gene they regulate, sometimes thousands of base pairs upstream or downstream.
- They work by DNA looping, bringing activator proteins bound to the enhancer close to the promoter.
