What type of bonds hold the two strands of a double helix together?

The strands of a double helix, such as that found in DNA, are held together primarily by hydrogen bonds. These bonds form between the nitrogenous bases of the two strands, where adenine pairs with thymine and guanine pairs with cytosine. The specific pairing allows for the stabilization of the structure while maintaining the flexibility necessary for biological functions such as replication and transcription.

Hydrogen bonds are relatively weak compared to other types of bonds; however, the cumulative effect of many such interactions across the length of the DNA molecule contributes to the overall stability of the double helix. This allows the strands to separate easily during processes like DNA replication—crucial for the hereditary transmission of genetic information.

While ionic bonds and covalent bonds play significant roles in the DNA structure (for instance, covalent bonds link the sugar and phosphate backbone of each strand), they do not hold the two strands together. Disulfide bridges are relevant in certain protein structures, but they do not pertain to the stability of the DNA double helix.