Practice question

Introns are intervening sequences interspersed between exons within transcription unit, transcribed into precursor RNA but excised during nuclear processing. Detected as discontinuities between genomic DNA and cDNA, introns vary from few base pairs to hundreds of kilobases, typically beginning GU and ending AG in mammals. Group I, II, and spliceosomal introns removed by different mechanisms; spliceosomal introns excised via lariat formation catalyzed by U1, U2, U5 snRNPs. Though non-coding, introns harbor regulatory RNAs, influence mRNA export, nonsense-mediated decay, and alternative splicing, distinguishing them as intragenic non-coding elements.