DNA: An Amazing Molecule
The structure of deoxyribonucleic acid (DNA) provides a com-plex code that encodes for synthesis of proteins. The DNA as a molecule exhibits many intriguing features. One useful prop-erty of DNA is that it readily anneals, meaning that it changes its binding properties in response to heating and cooling. Exposure to temperatures just below boiling (90–95°C) causes DNA to become temporarily denatured. When heat breaks open the hydrogen bonds that keep the double helix together, it sep-arates longitudinally into two strands. Each strand displays its nucleotide code so that the DNA in this form can be subjected to tests or replicated. When heating is followed by gradual cooling, two single DNA strands rejoin (renature) by hydrogen bonds at complementary sites. Annealing is a necessary feature of the polymerase chain reaction (PCR) and nucleic acid probes described later.