The nucleic acids are polymeric macromolecules made of repeated units called nucleotides. These consist in pentose sugar, nitrogenous base (purine or pyridimidine) and phosphate groups. In the living organisms due kinds of nucleic acids can be found: DNA and RNA .
The Watson and Crick hypothesis concerning the tridimensional structure of DNA is that it is formed by two purines: Adenine (A) and Guanine (G) and two pyridimidines: Cytosine (C) and Thymine (T) bound by phosphorylate sugars. Since DNA plays a key role as genetic material, the explanation of its tridimensional structure was essential in order to understand its functions. Wat- son and Crick’s deductions were deeply influenced by Linus Paulin description of hydrogenous bonds and alfa-helix. The fundamental characteristics are the DNA double helix where sugars and phosphates skeletal is oriented to the extern while the bases are oriented to the inside in such a way that an hydrogen bond can take place among purine and phyrimidine of opposite chains. The basis match is highly specific: A always binds with T and G with C. For this specific pairing, the two DNA chains are complementary: every chain contains all the needed information to determine the bases sequence of the other chain. The tridimensional RNA structure is represented by a simple chain made of C and uracil (U). The RNA decodes the DNA information, used to synthetize specif- ic proteins. The difference between DNA and RNA is that, while DNA has the essential function of containing information, the RNA carries out different functions in the cell and it is present in dif- ferent forms: mRNA, tRNA and rRNA.
The idea of searching for circulating DNA in plasm or serum came to the mind few years ago of a swiss physiologist who, noticed it in the plants’ lymph, had the idea to look for it in advanced tu- mor patients. He demonstrated its presence in radioimmunoassay essays. Later, other American labs published studies showing the tumoral origin of circulating DNA in plasm demonstrating the presence of genetic and epigenetic alterations typical of cancerous DNA in the plasmatic DNA in patients with different neoplasms like head and neck, lung, liver, pancreas, breast and prostate can- cer.
Huge de Vries in 1901 was the first to introduce the term “mutation” in the genetic field, observing how the trunk of the plant Oenothera Lamarckiana could produce unexpectedly large individuals. The concept of mutation, as it is intended today, has been used only from the 1927. Generally it can be said that genetic mutations play an essential role even before, from the very beginning of genet- ics; in his famous works the father of genetics, Gregor Mendel, the phenotypes like the white color of petals or the yellow color of the ripe seeds, used to formulate his laws, were caused by inactivat- ing mutations of the corresponding genes. A genetic mutation is every stable and heritable modifi- cation in the nucleic sequence in a genome or, more generally, in the genetic material (DNA and RNA) due to external factors or environmental interaction, and not due to genetic recombination. A mutations, therefor, modifies the individual genotype and it can lead to a phenotype modification.
