Sequence length: 20
GC content: 50%
Salt [Na⁺] mM: 50
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As temperature rises, hydrogen bonds break and the double helix denatures. GC pairs (3 bonds) melt at higher temperatures than AT pairs (2 bonds).
Nearest-neighbor thermodynamics: each dinucleotide step contributes ΔH and ΔS. The melting temperature Tm = ΔH/(ΔS + R·ln(CT/4)) where CT is total strand concentration. Cooperative helix-coil transition gives the characteristic sigmoidal shape.