Practice question

During first step of splicing, formation of lariat structure arises because nucleophilic attack uses two prime hydroxyl of branch adenine instead of three prime hydroxyl standard for phosphodiester bond. Resulting linkage between two prime position of adenosine ribose and five prime phosphate of intron five prime guanosine creates unusual two prime to five prime phosphodiester bond within intron, alongside conventional three prime to five prime bonds elsewhere. This branched Y-shaped intermediate appears as loop with tail. Specific debranching enzyme DBR1 hydrolyzes two prime-five prime bond to linearize intron for exonucleolytic decay.