Hyperchromicity

In their native state, the bases of DNA absorb light in the 260-nm wavelength region.

The hyperchromic effect is the striking increase in absorbance of DNA upon denaturation.

The two strands of DNA are bound together mainly by the stacking interactions, hydrogen bonds and hydrophobic effect between the complementary bases.

The double helix then separates into two single strands which are in the random coiled conformation.

At this time, the base-base interaction will be reduced, increasing the UV absorbance of DNA solution because many bases are in free form and do not form hydrogen bonds with complementary bases.