PNA
From Wikipedia, the free encyclopedia
- For other uses, see PNA (disambiguation).
PNA is peptide nucleic acid, a chemical similar to DNA or RNA but differing in the composition of its "backbone." PNA is not known to occur naturally in existing life on Earth but is artificially synthesized and used in some biological research and medical treatments.
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 methylene carbonyl bonds. PNAs are depicted like peptides, with the N-terminus at the first (left) position and the C-terminus at the right.
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 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 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 enzyme degradation. PNAs are also stable over a wide pH range. Finally, their uncharged nature should make crossing through cell membranes easier, which may improve their therapeutic value.
It has been hypothesized that the earliest life on Earth may have used PNA as a genetic material due to its extreme robustness, and later transitioned to a DNA/RNA-based system. This hypothesis is not widely considered likely, however. See RNA world hypothesis for related information.
[edit] External links
- An overview of the PNA molecule
- Recognition of chromosomal DNA by PNAs
- Alternative Nucleic Acid Analogues for Programmable Assembly: Hybridization of LNA to PNA
- The peptide nucleic acids (PNAs): a new generation of probes for genetic and cytogenetic analyses
- A New Game of Life
| Nucleic acids and oligonucleotides edit | ||
|---|---|---|
| Nucleobases: | Adenine | Thymine | Uracil | Guanine | Cytosine | Purine | Pyrimidine | |
| Nucleosides: | Adenosine | Uridine | Guanosine | Cytidine | Deoxyadenosine | Thymidine | Deoxyguanosine | Deoxycytidine | |
| Nucleotides: | AMP | UMP | GMP | CMP | ADP | UDP | GDP | CDP | ATP | UTP | GTP | CTP | cAMP | cADPR | cGMP | |
| Deoxynucleotides: | dAMP | TMP | dGMP | dCMP | dADP | TDP | dGDP | dCDP | dATP | TTP | dGTP | dCTP | |
| Ribonucleic acids: | RNA | mRNA | tRNA | rRNA | ncRNA | sgRNA | shRNA | siRNA | snRNA | miRNA | snoRNA | LNA | |
| Deoxyribonucleic acids: | DNA | mtDNA | cDNA | plasmid | Cosmid | BAC | YAC | HAC | |
| Analogues of nucleic acids: | GNA | PNA | TNA| LNA | morpholino | |
| ←Amino acids | Major families of biochemicals | Carbohydrates→ |
