What forms the bond between the two chains in a DNA double helix?

The bond between the two chains in a DNA double helix is formed by hydrogen bonds between the nitrogenous bases. In a DNA molecule, the two strands run in opposite directions and are held together at their bases, which are adenine (A), thymine (T), cytosine (C), and guanine (G). The specific pairing occurs through complementary base pairing where adenine pairs with thymine through two hydrogen bonds, and cytosine pairs with guanine through three hydrogen bonds.

These hydrogen bonds are crucial as they provide the necessary stability to the double helix while still allowing for the strands to separate during processes like DNA replication and transcription. This unique pairing is a key feature of DNA's structure and function, highlighting the importance of hydrogen bonds in maintaining the integrity and functionality of genetic material.

Other types of bonds mentioned, such as covalent bonds, are present within each individual DNA strand—connecting the sugar and phosphate backbone. However, they do not play a role in the interaction between the two strands. Peptide bonds are found in proteins, linking amino acids together, and disulfide bridges are covalent bonds that help stabilize protein structures, but neither of these is relevant to the structure of DNA.