Q.What type of linkages hold together monomers of DNA?

Step 1. DNA is a biopolymer whose repeating monomer unit is the nucleotide, itself built from a nitrogenous base, a deoxyribose sugar and a phosphate group (§14.5.1).

Step 2. Phosphoric acid forms a bond called a phosphodiester bond that bridges two neighbouring nucleotides: specifically, the phosphate group attached at the 5'-OH of one nucleotide's sugar forms an ester linkage to the free 3'-OH of the next nucleotide's sugar.

Step 3. Repeating this 5'→3' phosphodiester linkage many thousands of times over builds up the full polynucleotide chain, i.e. one strand of DNA.

Recall the nucleotide-to-nucleotide linkage chemistry from §14.5.1 -- a phosphate ester bridge between the 5' and 3' positions of adjacent sugar-phosphate units.

• Confusing the phosphodiester bond that links successive nucleotides ALONG one strand with the hydrogen bonds that link the two DNA STRANDS to each other across the double helix (§14.5.2) -- these are two entirely different bond types serving two different structural roles.