The mature mRNA has no introns
- The idea
- Predict
- See it
- Why
- Check
The idea
“The finished mRNA is the same as the transcript, with the introns still sitting between the exons.”
Exons and introns sit in one row in the gene, so it's easy to picture the message keeping that row. The cell edits it before it leaves the nucleus.
The short version
The mistake: The finished mRNA is the same as the transcript, with the introns still sitting between the exons.
What's actually true: Splicing cuts out the introns and joins the exons, so the mature mRNA holds only exons, plus a 5' cap and a poly-A tail.
- Transcription copies the exons and the introns alike. That first copy is the pre-mRNA.
- In the nucleus, a spliceosome cuts out the introns and joins the exons. The introns are broken down.
- A 5' cap and a poly-A tail are added. They protect the mRNA and help it get translated.
- Only this mature mRNA goes to the ribosome.
On the exam: Mature mRNA has its introns cut out, its exons joined, and a cap and tail.