Peptide nucleic acid
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2008-04-30T11:38:24Z
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[[Image:PNA en.svg|right|]]
'''Peptide nucleic acid''' (PNA) is an artificially synthesized [[polymer]] similar to [[DNA]] or [[RNA]] and is used in biological research and medical treatments. PNA is not known to occur naturally.
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 bond]]s. The various [[purine]] and [[pyrimidine]] bases are linked to the backbone by [[methylene]] [[carbonyl]] bonds. PNAs are depicted like [[peptide]]s, with the [[Nitrogen|N]]-terminus at the first (left) position and the [[Carbon|C]]-terminus at the right.<ref>Egholm, M., Buchardt, O., Christensen, L., Behrens, C., Freier, S.M., Driver, D. A., Berg, R.H., Kim, S.K., Nordén, B. and Nielsen, P.E. PNA Hybridizes to Complementary Oligonucleotides Obeying the Watson-Crick Hydrogen Bonding Rules. (1993) Nature, 365, 566-568.</ref>
Since the backbone of PNA contains no charged [[phosphate]] groups, the binding between PNA/DNA strands is stronger than between DNA/DNA strands due to the lack of electrostatic repulsion. Early experiments with homopyrimidine strands (strands consisting of only one repeated [[pyrimidine]] base) have shown that the T<sub>m</sub> ("melting" temperature) of a 6-base thymine PNA/adenine DNA double helix was 31°C in comparison to an equivalent 6-base DNA/DNA duplex that [[denaturation (biochemistry)|denatures]] at a temperature less than 10°C. Mixed base PNA molecules are true mimics of DNA molecules in terms of base-pair recognition. PNA/PNA binding is stronger than PNA/DNA binding.
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 [[nuclease]]s or [[protease]]s, making them resistant to [[enzyme]] degradation. 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.
It has been hypothesized that the earliest life on [[Earth]] may have used PNA as a genetic material due to its extreme robustness, simpler formation and possible spontaneous [[polymerization]] at 100°C<ref>Wittung, P., Nielsen P.E., Buchardt, Ole., Egholm, M. and Nordén, B. DNA-like Double Helix formed by Peptide Nucleic Acid. (1994) Nature, 368, 561-563.</ref> (while water at standard pressure boils at this temperature, water at high pressure - as in deep ocean - boil at higher temperatures). If this is so, life [[chemical evolution|evolved]] to a DNA/RNA-based system only at a later stage<ref>Nelson, K.E., Levy, M., and Miller, S.L. [http://www.pnas.org/cgi/content/abstract/97/8/3868 Peptide nucleic acids rather than RNA may have been the first genetic molecule] (2000) Proc. Natl. Acad. Sci. USA 97, 3868–3871.</ref>
<ref>Alberts, Johnson, Lewis, Raff, Roberts and Walter, ''Molecular Biology of the Cell'', 4th Edition, Routledge, March, 2002, ISBN 0-8153-3218-1.</ref>. Evidence for this hypothesis is however far from conclusive. See [[RNA world hypothesis]] for related information.
==See also==
*[[Glycerol nucleic acid]]
*[[Threose nucleic acid]]
==References==
<references/>
==External links==
*[http://www.horizonpress.com/gateway/pna.html An overview of the PNA molecule]
*[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15217608 Recognition of chromosomal DNA by PNAs]
*[http://pubs.acs.org/cgi-bin/sample.cgi/nalefd/2005/5/i01/abs/nl048246f.html Alternative Nucleic Acid Analogues for Programmable Assembly: Hybridization of LNA to PNA]
*[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=15581832 The peptide nucleic acids (PNAs): a new generation of probes for genetic and cytogenetic analyses]
*[http://sciencewriter.org/protocells/ A New Game of Life]
{{Nucleic_acids}}
[[Category:Nucleic acids]]
[[Category:Origin of life]]
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[[fr:Acide nucléique peptidique]]
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[[ja:ペプチド核酸]]
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[[ru:Пептидо-нуклеиновые кислоты]]
[[zh:肽核酸]]
[[tr:Peptit Nükleik Asit]]