Why Does Denatured DNA Absorb More Ultraviolet Light Than Double-Stranded DNA?

The phenomenon of UV absorbance increasing as DNA is denatured is known as the hyperchromic shift. The purine and pyrimidine bases in DNA strongly absorb ultraviolet light. Double-stranded DNA absorbs less strongly than denatured DNA due to the stacking interactions between the bases. Single deoxynucleotides absorb more strongly than denatured DNA⁽¹⁾.

1. Alexander, R.R. and Griffiths, J.M. (1993) Basic Biochemical Methods, 2nd Edition. J.M. Wiley and Sons, New York.