DNA is found in the nucleus (bacteria in the mimic nucleus, viruses within the protein shell), copy mitochondria, chloroplasts (in the case of plants) RNA is found in the cytoplasm (viruses within the protein shell, with DNA there is no RNA).

　　The double helix structure of the DNA molecule is relatively stable. This is because on the inner side of the double helix structure of the DNA molecule, two long strands of deoxyribonucleotides are firmly linked in parallel by the formation of bases through hydrogen bonds. In addition, the longitudinal interaction between the base pairs further reinforces the stability of the DNA molecule.

　　This longitudinal interaction between the base pairs is called base stacking force, which is the aromatic base π electron interactions caused by the degree.

　　It is now generally accepted that the base stacking force is the most important factor in stabilising the structure of DNA. Then there is the negative charge of the phosphate group on the outside of the double helix with the positive charge of the cation between the formation of the ionic bond, can reduce the electrostatic repulsion between the double strand, and thus the DNA double helix structure is also a certain stabilizing effect.

　　DNA molecules due to the number of different base pairs, the order of the base pairs is varied, thus constituting the diversity of the DNA molecule. For example, a DNA molecule with 4,000 base pairs carries four types of genetic information, i.e. 10 types.