Properties of DNA
1) The size of the DNA molecule: The size of the DNA molecule varies from organism to organism. It depends upon the size of the chromosome and the number of chromosomes found in each living cell. The size basically depends on the number of nucleotide present in each DNA molecule. The size of DNA molecule ranges from 0.7 mm to 40,000 mm.
2) Fragility of DNA molecule: The DNA molecule is highly fragile. The fragility of DNA molecule is determined by its length. Larger molecules break easily. But smaller molecules are not susceptible to breakage.
The DNA molecule is highly susceptible to breakage during handling operations, such as mixing, pipetting, pouring, etc. So the smaller molecules with less than 2x10 power of 8 daltons molecular weight are isolated without damage. The large sized DNA's undergo breakage during their extraction.
3) Denaturation: Denaturation refers to the separation of the two strands of a DNA. Denaturation is brought about by high temperature, acid or alkali.
Denaturation is brought about by the breakdown of hydrogen bonds between base pairs. Since G-C base pairs have three hydrogen bonds and A-T pairs have two hydrogen bonds, the region of DNA containing G-C base pairs is more stable and it requires high temperature or pH for denaturation.
Denaturation begins in the regions rich in A-T base pairs and progressively extends to the regions of increasing G-C content.
4) Renaturation: The denatured single stranded DNA can be made into double stranded DNA by cooling or neutralizing the medium. This process is called renaturation.
5) Effect of pH on DNA: The DNA is stable around the neutral pH in the solution. Further increase in pH causes strand separation and finally denaturation occurs above pH 11.3.
6) Stability: The DNA is a highly stable molecule. The stability is due to two forces:
a) Hydrogen bonding between the bases.
b) Hydrophobic interactions between bases.
7) Hyperchromic Effect: DNA molecule absorbs light energy. This is a property of individual bases.
The intact DNA absorbs less light energy as its bases are packed into a double helix.
A denatured DNA molecule absorbs more light as its bases in single strands are exposed. The increase in the absorption of light occurs even though the amount of DNA remains the same. This phenomenon of increased light absorption is called hyperchromic effect.
A single stranded DNA does not show the hyperchromic effect. This phenomenon of hyperchromic effect can be used to distinguish single or double stranded DNAs in the sample.