The promoter, cap and tail never become protein
- The idea
- Predict
- See it
- Why
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The idea
“The promoter, cap and poly-A tail are part of the code, so they become protein.”
On a gene diagram, the promoter, cap and tail sit in a line with the codons, so they look like more code. None of them is ever read as codons.
The short version
The mistake: The promoter, cap and poly-A tail are part of the code, so they become protein.
What's actually true: Only the codons from AUG up to the stop codon become protein. The promoter, cap and tail mark where to bind, start or protect.
- A promoter is a DNA sequence where RNA polymerase binds to start transcription. It isn't copied into mRNA.
- In eukaryotes, a 5' cap and poly-A tail are added to the mRNA. They help it leave the nucleus and protect it from breakdown.
- The cap also helps the ribosome attach. Only the codons from AUG up to the stop codon become amino acids.
On the exam: Only AUG to stop becomes protein. The promoter, cap and tail are signals.