The physics of nucleic acids deals with the study of molecular structure–property relationship to describe life phenomena, in particular heredity and variability. The origin and development of molecular biophysics is associated with the genetic role of nucleic acids and with their interpretation. Physics has played a vital role in providing a foundation to molecular biology. For instance, the discovery of the DNA duplex structure was facilitated by data obtained from the X-ray diffraction studies by Watson and Crick (1953). They proposed a structure which has two helical chains each coiled around the same axis. The bases are located inside the helix whereas the phosphates on the outside. Schrödinger (1944) has discussed these issues in his book What is Life? In biomolecules, the relation between the molecular structure and its biological function is not trivially correlated. Due to high linear charge density, the DNA molecule acts as a strong polyelectrolyte. It is twisted into a very loose coil in its single strand conformation. Such a coil is associated with a persistence length of 50 nm in a 0.15M NaCl solution whereas it is 80 nm in a 0.0015M NaCl dispersion. We shall discuss some structural as well as functional aspects of these informational molecules in the following sections.

DNA stacking

Let us look at some examples of simple models that describe base pair stacking. We already know that for DNA the matching base pairs are A-T and G-C, while for RNA, it is A-U and G-C.