The fact that the DNA molecule is made of two polynucleotide chains whose nitrogen-containing bases form hydrogen bonds facilitate the duplication of the molecule. During the DNA replication, the binding of the two chains is broken and each of them serves as a template for the formation of a new nucleotide sequence along with it, with the help of the enzyme DNA polymerase and obeying the pairing rule A-T, C-G. At the end of the process two double helix of DNA are produced, each made of an original template chain and of a newly synthesized polynucleotide chain.