Practice question

Exon terminology from expressed region denotes segments of transcription unit that persist in mature messenger RNA after intron removal by spliceosome. Exons include both protein-coding stretches and non-coding 5' and 3' untranslated regions that influence stability and translation efficiency. In pre-mRNA, exon-intron boundaries defined by conserved GU at 5' splice site, AG at 3' site, and branch adenosine. Spliceosome catalyzes two sequential transesterification reactions ligating exons. Because exon shuffling creates novel domain combinations, retention rather than removal defines exon functionally as information retained post-processing for export.