Here's why:

* Nucleotides are the monomers (building blocks) of DNA. Each nucleotide consists of a sugar (deoxyribose), a phosphate group, and a nitrogenous base (adenine, guanine, cytosine, or thymine).

* Poly means "many."

* Nucleotides are linked together in a chain to form a polynucleotide.

So, a DNA molecule is essentially a very long polynucleotide chain.