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Denaturation disrupts hydrogen bonding and base stacking in DNA, separating strands while leaving the phosphodiester backbone intact. Heat, extreme pH, chemical denaturants, low ionic strength, and mechanical shear can promote this change. As bases become unstacked, absorbance at 260 nm increases; melting temperature (Tm) marks the point at which half of the DNA is single-stranded. Tm is influenced by GC content, salt concentration, length, and mismatches. Renaturation, or annealing, depends on complementary sequences and suitable conditions, including slow cooling and sufficient salt. The balance between strand separation and reassociation is important in hybridization assays and PCR, while RNA secondary structures may also be managed during electrophoresis.