In eukaryotes, a gene often contains altereing sequences known as exons and introns. In contrast to prokaryotes, which do not have introns, the primary mRNA transcript (see transcription) from the DNA has to be spliced, that means, the introns are removed form the mRNA in an [intramolecular reaction]?, where the mRNA acts as a ribozyme?. Mutations in the introns can prevent splicing and thus protein biosynthesis.
XXXXEEEEIIIEEEEEEEEEEIIIIEEEEEEEEEEXXXX DNA with exons and introns ↓transcription↓ EEEEIIIEEEEEEEEEEIIIIEEEEEEEEEE mRNA (primary transcript) with exons and introns ↓ splicing ↓ EEEEEEEEEEEEEEEEEEEEEEEE mRNA (spliced) with exons ↓ translation ↓ protein