what holds one strand against the other in the double helix?

The two strands of the DNA double helix are held together primarily by hydrogen bonds between complementary nitrogenous bases. Adenine (A) pairs with thymine (T) via two hydrogen bonds, while guanine (G) pairs with cytosine (C) via three hydrogen bonds. These hydrogen bonds form between bases on opposite strands, stabilizing the double helix structure. Additionally, the sugar- phosphate backbones of each strand are held together internally by strong covalent phosphodiester bonds, but it is the hydrogen bonding between bases that holds one strand against the other in the double helix. The strands run antiparallel to each other, meaning their orientations are opposite, which is crucial for proper base pairing and helix formation