In fact, two strands of DNA that are complementary to one another actually bind to form a double stranded DNA. And that double stranded DNA forms a coil that we call the double helix. And the two single stranded DNAs bond to one another via a special type of dipole dipole bond known as hydrogen bonds. So the thing that holds our two strands of DNA together to form our double helix are hydrogen bondings or hydrogen bonds between adjacent or opposite nucleotide, specifically our nitrogenous basis. So we have this nucleotide, which is right next to this nucleotide, and the bonding takes place between our adjacent or complementary nitrogenous bases. So guanine always forms hydrogen bonds with cytosine, while our Adamine always forms hydrogen bonds with arithymine.