Peptide nucleic acid (PNA) is an artificially synthesized polymer similar to DNA or RNA. It was invented by Peter E. Nielsen (Univ. Copenhagen), Michael Egholm (Univ. Copenhagen), Rolf H. Berg (Risø National Lab), and Ole Buchardt (Univ. Copenhagen) in 1991.
Synthetic peptide nucleic acid oligomers have been used in recent years in molecular biology procedures, diagnostic assays, and antisense therapies. Due to their higher binding strength it is not necessary to design long PNA oligomers for use in these roles, which usually require oligonucleotide probes of 20–25 bases. The main concern of the length of the PNA-oligomers is to guarantee the specificity. PNA oligomers also show greater specificity in binding to complementary DNAs, with a PNA/DNA base mismatch being more destabilizing than a similar mismatch in a DNA/DNA duplex. This binding strength and specificity also applies to PNA/RNA duplexes. PNAs are not easily recognized by either nucleases or proteases, making them resistant to degradation by enzymes. PNAs are also stable over a wide pH range. Though an unmodified PNA cannot readily cross cell membranes to enter the cytosol, covalently coupling a cell penetrating peptide to a PNA can improve cytosolic delivery.
PNA is not known to occur naturally but N-(2-aminoethyl)-glycine (AEG), the backbone of PNA, are possibly an early form of genetic molecules for life on earth and produced by cyanobacteria.
DNA and RNA have a deoxyribose and ribose sugar backbone, respectively, whereas PNA's backbone is composed of repeating
N-(2-aminoethyl)-glycine units linked by peptide bonds. The various purine and pyrimidine bases are linked to the backbone by a methylene bridge (-CH 2-) and a carbonyl group (-(C=O)-). PNAs are depicted like peptides, with the N-terminus at the first (left) position and the C-terminus at the last (right) position.