Absorbance  Since purines and  pyrimidines show maximum absorbance in the ultraviolet region of the spectrum at 260nm, this property is useful in determining  the amount of DNA with a spectrophotometer. When the native DNA is denatured, there is increased absorbance due to the decrease in the number of hydrogen bonds. This change is known as the hyperchromic effect.

lonic interaction  DNA behave like a polyelectrolyte because the phosphate groups that lie on the outer surface of DNA impart an anionic character to it. The Phosphate groups are ionized at physiological pH so that the DNA is capable to interacting with a number of cations. In eucaryotes, DNA is always associated with histones which are positively charged.

Denaturation The double helix cannot withstand to disruptive forces of heating. When a salt solution of DNA is heated to 70 – 80^o C, the two strands separate due to the breaking of hydrogen bonds and this brings about a change in the viscosity, absorbance and optical rotation of the DNA.

This property is called denaturation or melting. The solution containing DNA is slowly heated until a critical temperature is reached when strand separation begins. This temperature Tm is specific for a given DNA preparation and it reflects the base composition of the DNA. AT –rich segments of DNA melt earlier C  G content affords greater stability to the molecule. Thus, the higher the C  G content, the higher is the Tm value.

On slow cooling the two strands region with the reformation of hydrogen bonds restoring  the  helical configuration. This is called renaturation or annealing of DNA, a Behavior that has wide-ranging implications hybridization experiments.


Molecule weight  Viral and bacterial DNAs are linear or circular and the genetic information of each molecule depends on the number of nucleotide pairs and length of the molecule which ultimately help in the determination of molecular weight. Eucaryotic DNA is complex and large, and invariably associated with proteins, and hence its molecular weight cannot be determined easily.

Viscosity DNA molecules are large and cab be fragmented. The fragments in solution become highly viscous and may be removed by moving a glass rod thorough the solution. The fragments stick on to the rod. Single stranded DNA molecule is identical to that of CsCl. This technique has been particularly useful in isolation different kinds of DNA, and to separate native DNA from the denatured or non-helical variety. Spinning in a high-speed concentration is lowest at the top and highest in the bottom of the tube. The molecule occupy regions in CsCl solution in accordance to their buoyant density matching with that of CsCl.

Sedimentation  the density gradient centrifugation technique is employed to analyze DNA.  A sample of DNA is taken in CsCl and spun in a centrifuge which gives a characteristic banding where the density of the DNA molecule is identical to that of CsCl. This technique has been particularly useful in isolating different kinds of DNA, and to separate native DNA from the denatured or non-helial variety. Spinning in a high-speed centrifuge enables the distribution of CsCl solution in a way that its concentration is lowest at the top and highest in the bottom of the tube. The molecule occupy regions in CsCl solution in accordance to their buoyant density matching with that of CsCl.