- Peptide nucleic acid
Peptide nucleic acid (PNA) is an artificially synthesized
polymersimilar to DNAor RNAand is used in biological research and medical treatments. PNA is not known to occur naturally.
DNA and RNA have a
deoxyriboseand ribosesugar backbone, respectively, whereas PNA's backbone is composed of repeating N-(2-aminoethyl)-glycine units linked by peptide bonds. The various purineand pyrimidinebases are linked to the backbone by methylene carbonylbonds. PNAs are depicted like peptides, with the N-terminus at the first (left) position and the C-terminus at the right. [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.]
Since the backbone of PNA contains no charged
phosphategroups, 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 pyrimidinebase) have shown that the Tm ("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 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
antisensetherapies. 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 enzymedegradation. PNAs are also stable over a wide pHrange. Though an unmodified PNA cannot readily cross cell membranes to enter the cytosol, covalently coupling a cell penetrating peptideto a PNA can improve cytosolic delivery.
It has been hypothesized that the earliest life on
Earthmay have used PNA as a genetic material due to its extreme robustness, simpler formation and possible spontaneous polymerizationat 100°C [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.] (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 evolved to a DNA/RNA-based system only at a later stage [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.] [Alberts, Johnson, Lewis, Raff, Roberts and Walter, "Molecular Biology of the Cell", 4th Edition, Routledge, March, 2002, ISBN 0-8153-3218-1.] . Evidence for this hypothesis is however far from conclusive. See RNA world hypothesisfor related information.
Glycerol nucleic acid
Threose nucleic acid
* [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]
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Look at other dictionaries:
peptide nucleic acid — noun A compound analogous to DNA in which a synthetic peptide takes the place of the sugar in DNA • • • Main Entry: ↑pepsin … Useful english dictionary
Peptide Nucleic Acid — Acide nucléique peptidique Pour les articles homonymes, voir ANP et PNA. L acide nucléique peptidique (ANP) ou Peptide Nucleic Acid, (PNA) en anglais, est une molécule aux bases similaires à l ADN ou à l ARN mais qui se différencie par son… … Wikipédia en Français
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