Final answer:
Bases in DNA are bound together by hydrogen bonds, which stabilize the base pairs within the DNA double helix. Phosphodiester bonds link the sugar-phosphate backbones rather than the bases.
Step-by-step explanation:
Bases are bound together via hydrogen bonds. This type of bond is pretty significant. It enables adenine to pair with thymine (A-T), forming two hydrogen bonds, and guanine to pair with cytosine (G-C), forming three hydrogen bonds. These hydrogen bonds are responsible for stabilizing the base pairs at the interior of the DNA double helix. While hydrogen bonds are weaker than covalent bonds, they are still essential for the structure of DNA. The phosphodiester bonds, on the other hand, play a different role in DNA structure as they bond the sugar-phosphate backbones together, not the complementary bases themselves.