Practice question

Group I introns are self-splicing ribozymes catalyzing their own excision via two transesterification steps that require external guanosine cofactor. Free guanosine or GMP, GDP, GTP binds specific G-binding pocket in P7 paired region of intron tertiary structure. Its 3' hydroxyl serves as nucleophile attacking 5' splice site, becoming covalently attached to intron 5' end, freeing upstream exon. Second attack by upstream exon 3' OH on 3' splice site ligates exons. No ATP hydrolyzed, reversible, aided in vivo by maturases. This refined regulation supports accurate ribosomal assembly, quality control and translational fidelity under diverse physiological conditions and growth states.