DNA double helix is maintained by:

In a DNA double helix, two polynucleotide strands come together through complementary pairing of the bases, which occurs by hydrogen bonding.Each base forms hydrogen bonds readily to only one other -- A to T and C to G -- so that the identity of the base on one strand dictates what base must face it on the opposing strand.Thus the entire nucleotide sequence of each strand is complementary to that of the other, and when separated, each may act as a template with which to replicate the other.