Table: 3-1.1 The relationship between concentration of DNA, RNA, Protein and absorptivity are as below:

¹ "Antibodies: A Laboratory Manual", by E. Harlow, and D. Lane, p. 673. Academic Press, New York., 1988.

The purity of a solution of nucleic acid is determined by measuring the absorbance of the solution at two wavelengths, usually 260 nm and 280 nm, and calculating the ratio of A ₂₆₀ /A _280- . Value of this ratio is 2.0, 1.8and 0.6 for pure RNA, DNA and protein respectively. A ratio of less than 1.8 signifies that the sample is contaminated with protein or phenol and the preparation is not proper.

Fig 3-1.3.1: UV detection of nucleic acids

Hyperchromicity is the phenomenon of increment of absorbance when any material is exposed to UV light.The most well known application is the hyperchromicity of DNA that occurs when the DNA duplex is denatured and melting of DNA occurs. The UV absorption is increased when the duplex DNA strands are being separated into single strands, either by heat or by addition of denaturant or by increasing the pH level. On the contrary, decrease of absorbance peak is called hypochromicity.

Fig. 3-1.3.1.1: Nucleic acid melting curve showing hyperchromicity as a function of temperature