Practice question

Antisense oligonucleotides synthetic single-stranded nucleic acids 16-20 nucleotides bearing phosphorothioate backbone replacing nonbridging oxygen sulfur increasing nuclease resistance albumin binding prolonging half-life, 2 prime O-methoxyethyl sugar increasing affinity Tm 2 degrees per modification reducing immune stimulation TLR7/8, locked nucleic acids constraining ribose C3 endo enhancing hybridization strength. Binding target mRNA via Watson-Crick pairing forming heteroduplex nucleus or cytoplasm, two mechanisms dominate: recruitment endogenous RNase H1 hydrolyzing RNA strand DNA-RNA hybrid degrading transcript, and steric blocking preventing spliceosome U1 snRNP recognition 5 prime splice site or 40S scanning initiation complex finding start codon. Applications inotersen RNase H degradation transthyretin mRNA hereditary amyloidosis, nusinersen splicing modulation enhancing SMN2 exon 7 inclusion spinal muscular atrophy, eteplirsen exon 51 skipping restoring dystrophin reading frame. Conjugation N-acetylgalactosamine triantennary ligand enables asialoglycoprotein receptor-mediated hepatocyte uptake permitting subcutaneous dosing durable suppression. This mechanistic insight guides vector optimization, dosing strategies, and clinical safety monitoring essential for translational development and regulatory evaluation.