An exon is a region of a gene that ends up within an mRNA molecule and codes for amino acids. Exons are the protein-coding parts of the RNA plus the untranslated regions of the mRNA (UTR exon mRNA) plus some part that’s actually the non-coding RNA. After transcription, new, immature strands of messenger RNA, called pre-mRNA, may contain both introns and exons. These pre-mRNA molecules go through a modification process in the nucleus called splicing during which the noncoding introns are cut out and only the coding exons remain. Splicing produces a mature messenger RNA molecule that is then translated into a protein. Some exons are coding, in that they contain information for making a protein, whereas others are non-coding. The term exon derives from the expressed region and was coined by American biochemist Walter Gilbert in 1978.