What type of bond holds the two strands of DNA together?

The correct answer is that hydrogen bonds hold the two strands of DNA together. DNA is composed of two strands that form a double helix structure. These strands run in opposite directions and are connected by pairs of nitrogenous bases: adenine pairs with thymine, and guanine pairs with cytosine. The specific pairing is stabilized by hydrogen bonds, which are relatively weak interactions compared to covalent or ionic bonds. This allows the DNA strands to be separated easily during processes such as replication and transcription, while still providing enough stability for the overall structure to remain intact.

The strength and specificity of hydrogen bonds are crucial for the proper functioning of DNA, as they enable the precise matching of base pairs that codes for genetic information. The other types of bonds mentioned do not play a role in holding the DNA strands together in the same manner. Ionic bonds, for example, typically occur between charged ions and do not contribute to the specific base pairing in DNA, while covalent bonds primarily connect atoms within each individual DNA strand (such as the bond between the sugar and phosphate groups in the backbone). Metallic bonds are not relevant in this biological context. Thus, the hydrogen bonds are essential for the structural integrity and function of DNA strands in the double helix formation.