Practice question

Hybridization stability depends on chemical composition and physicochemical environment. Guanine-cytosine pairs contain three hydrogen bonds versus two for adenine-thymine, and stronger base-stacking interactions, conferring higher thermodynamic stability and elevated melting temperature. Elevated monovalent cation concentration, such as high salt, stabilizes duplex by shielding electrostatic repulsion between negatively charged phosphate backbones. High temperature destabilizes mismatched duplexes but GC-rich sequences retain annealing due to greater enthalpy. Therefore combination of GC-rich sequence with high salt maintains most stable hybrid despite thermal stress, whereas AT-rich or low salt conditions favor dissociation.