Final answer:
The phosphodiester bond holds neighboring subunits together in a single DNA strand, while hydrogen bonds between base pairs hold the two strands of the DNA double helix together.
Step-by-step explanation:
The type of bond that holds together neighboring subunits in a single strand of DNA is the phosphodiester bond, which is a type of covalent bond. However, it's worth noting that hydrogen bonds are responsible for holding the two strands of the DNA double helix together, facilitating the base pairing between nucleotides of opposite strands (for example, A with T, and C with G).
These hydrogen bonds allow the DNA double helix to 'unzip' for replication and transcription, since they are weaker than the covalent bonds in the DNA backbone.