Introns are cut out of the RNA copy
- The idea
- Predict
- See it
- Why
- Check
The idea
“Introns get cut out of the DNA, or skipped while the gene is being copied.”
Introns never reach the protein, so deleting them from the gene seems simplest. The cell edits the RNA copy instead.
The short version
The mistake: Introns get cut out of the DNA, or skipped while the gene is being copied.
What's actually true: Every exon and intron of a gene is copied into pre-mRNA. The introns are then cut out of that RNA, and the DNA keeps them.
- Exons end up in mature mRNA. Introns are the stretches between them that get removed.
- RNA polymerase copies the introns right along with the exons. That first copy is pre-mRNA.
- Spliceosomes, made of proteins and small RNAs, cut the introns out of pre-mRNA in the nucleus and join the exons.
- The gene in the DNA keeps its introns. To get an intron-free copy for bacteria, labs use reverse transcriptase to copy mature mRNA back into DNA.
On the exam: Introns are copied into RNA, then cut from the RNA. The gene in the DNA keeps them.