Because in this particular case, we have the stacking of these bases and we have vanderbal forces and hydrogen bonds. And those bonds will essentially decrease the amount of UV radiation that can be absorbed by those bases. So how can we measure the dissociation of DNA molecules in solution? Well, it turns out that the amount of UV radiation, UV light, where UV stands for ultraviolet absorbed by DNA molecules, increases as the DNA dissociates. So as we shine light onto our solution, as we heat that solution, eventually that solution will begin to absorb more and more UV radiation. And we can plot that on a graph.