PNA means Peptide Nucleic Acid , it does not exist Sigle in French. They is molecules at the bases similar to the DNA or the ARN but which is different by its skeleton (" backbone" in English). The PNA are not known to exist naturally on Earth. They are synthéstisés artificially and used in the medical research and certain therapies.

DNA and ARN respectively have sweetened residues of Désoxyribose or Ribose which composes their skeletons. In the case of the PNA, the skeleton are composed of a repetition of units N (2-aminoethyl) - glycine connected by a peptide Liaison. The bases Purin and Pyrimidine are attached to the skeleton by bonds methyl carbonyl. The PNA are thus noted like Peptide S, with the N-final end in first position (left) and the C-final end in last position (right).

The skeleton of the PNA thus does not contain grouping Phosphate (charged), which has as consequence which connection PNA/ADN is stronger than a traditional connection ADN/ADN because of electrostatic absence of repulsion. Preliminary experiments carried out with bits of homopyrimidine (bits made up of a repetition of only one base, the Pyrimidin) showed that T_m (" melting" temperature or temperature of hybridization) of a double helix PNA (constituted of 6 bases of Thymine)/DNA (compound of Adenine) was of 31°C. In comparison, equivalent ADN/ADN is denatured has a temperature lower than 10°C. The recognition between bases is perfect between DNA and the PNA.

PNA were used recently in Molecular biology like diagnostic tools and within the framework of therapeutic strategies Antisens. Because of their large affinity for DNA or ARN, it is not necessary to work with long oligomers for these uses which traditionally require probes oligos of 20-25 bases. The problem is then to be able to ensure a better specificity. The PNA also have the characteristic at the time of their connection to the ARN or DNA to be destabilized by 1 or 2 mésappariemments (" mismatch"). The PNA are not recognized by the Nucléase S or the Protéase S what makes them resistant to the enzymatic degradations. The PNA are also stable in an important range of pH. With final, the fact that they are not charged and of small size represents an advantage to cross the plasmic membrane. That remains however the factor limiting in a therapeutic use, the cellular methods of penetration not being adapted to this absence of loads. Once this raised limitation, a strong potential will open with these molecules.

It is supposed that primitive forms of life on Ground could use PNA like genetic material because of their high strength and then evolve to a system based on the ADN/ARN. This hyphothèse remains however far from probable. See the article devoted to with the origins of life for more information on this subject.

External bonds

• a review on the PNA (in English)