When DNA is denatured, the hydrogen bonds that hold the double helix together break apart, separating the DNA molecule into two single strands. Denaturation occurs as the temperature increases, according to Ian VanLare, Professor of Biology at Tusculum College.
The melting temperature of DNA depends on three factors. One is the number of guanine and cytosine pairs in the sample. This is because G-C pairs share three hydrogen bonds, while pairs of adenine and thymine share only two hydrogen bonds. The second factor is sodium concentration. Increased sodium concentration increases the stability of the DNA double helix, while decreased sodium concentration makes the double helix less stable. Finally, the length of a DNA hybrid also affects melting temperature. This is because longer hybrids have more hydrogen bonds to break during denaturation.
It is possible to replicate one strand of DNA after it has been denatured. Scientists do this by adding a short piece of DNA at one end of the single strand. This piece of DNA is called a primer. Then the scientist adds an enzyme called DNA polymerase. This enzyme recognizes the bases on the single strand of DNA and adds complementary bases to the new strand of DNA.