Intronplugin-autotooltip__default plugin-autotooltip_bigIntron: sequences in a pre-mRNA that sit between exons and are removed by splicing. Formally speaking, introns are defined as being part of pre-mRNA, but the DNA sequence that codes for introns can also be informally described as introns. splicing: the act of remove intronsplugin-autotooltip__default plugin-autotooltip_bigIntron: sequences in a pre-mRNA that sit between exons and are removed by splicing. Formally speaking, introns are defined as being part of pre-mRNA, but the DNA sequence that codes for introns can also be informally described as introns. and joining exonsplugin-autotooltip__default plugin-autotooltip_bigExon: the portion of a pre-mRNA that contains codons. pre-mRNAs usually contain multiple exons that are interspersed with introns. Formally, exons are defined as a component of pre-mRNA, but the DNA sequence that codes for exons can also be informally referred to as exons. from pre-mRNAplugin-autotooltip__default plugin-autotooltip_bigpre-mRNA: In eukaryotes, genes are transcribed as a longer RNA molecule called pre-mRNA, which is then processed via splicing, 5'-capping, and 3' polyadenylation before it is transported into the cytoplasm and becomes a mature mRNA. to form an mRNAplugin-autotooltip__default plugin-autotooltip_bigmessenger RNA (mRNA): an RNA molecule that codes for protein.. This occurs in the nucleusplugin-autotooltip__default plugin-autotooltip_bigNucleus: in eukaryotes, the membrane-bound organelle in cells that contains the chromosomes. of eukaryoticplugin-autotooltip__default plugin-autotooltip_bigeukaryote: organism whose cells have membrane bound organelles, including the nucleus. cells and is catalyzed by an enzymeplugin-autotooltip__default plugin-autotooltip_bigEnzyme: a macromolecule, usually a protein (but sometimes an RNA), that functions as a catalyst of some kind of biochemical reaction. called the spliceosomeplugin-autotooltip__default plugin-autotooltip_bigSpliceosome: a large and complex enzyme located in the nucleus of eukaryotic cells that catalyzes intron splicing..