What type of bond links nucleotides together in a DNA strand?

A phosphodiester bond links neighboring nucleotides together in a DNA strand. It connects the 3′ hydroxyl group of one deoxyribose sugar to the 5′ phosphate group of the next nucleotide, creating the continuous sugar-phosphate backbone.

The term “phosphodiester” refers to a phosphate group joined through two ester linkages to two sugars. Repeating bonds of this kind give each DNA strand a direction, running from a 5′ end to a 3′ end. The two strands of the double helix run antiparallel, meaning their directions are opposite.

Although a phosphodiester bond is a type of covalent bond, “covalent bond” is too broad to be the best answer to this question. Ionic bonds are not what forms the DNA backbone, and hydrogen bonds primarily connect complementary bases between the two strands.

The backbone’s negatively charged phosphate groups also influence how DNA interacts with proteins and ions. Enzymes such as DNA polymerases build new DNA strands by forming phosphodiester linkages, while nucleases break these bonds during DNA processing and repair.