Practice question

EdU, 5-ethynyl-2'-deoxyuridine, retains Watson-Crick pairing but bears terminal alkyne at 5 position instead of bromine. Detection utilizes bioorthogonal click chemistry specifically copper(I)-catalyzed azide-alkyne cycloaddition first described by Sharpless. In this reaction, alkyne on EdU incorporated into DNA reacts with fluorescent azide forming stable 1,2,3-triazole covalent linkage, catalyzed by CuSO4 reduced to Cu(I) by sodium ascorbate, proceeding rapidly in aqueous buffer at room temperature with exquisite specificity. Because fluorescent azide small molecule penetrates duplex DNA, harsh denaturation required for BrdU antibody access unnecessary. Standard BrdU assays need 2M hydrochloric acid, 95°C heat, or DNase digestion to unwind helix exposing brominated base for antibody binding, steps that destroy protein epitopes and fluorescent proteins. Click reaction eliminates antibody step, shortens protocol from overnight incubation to less than one hour, preserves morphology, and allows multiplexing with surface markers. Unlike radioactive thymidine labeling, EdU non-radioactive and bright. This advance revolutionized proliferation assessment. Nobel Prize in Chemistry 2022 recognized click chemistry applications transforming biological labeling and drug discovery. This knowledge strengthens laboratory safety, protocol reproducibility, and regulatory compliance critical for translational research and clinical applications, ensuring reliable data and workforce protection.