Here's a breakdown:

* DNA (Deoxyribonucleic acid) is a long, complex polymer that carries genetic information.

* Nucleotides are the building blocks of DNA. Each nucleotide consists of three components:

* A sugar molecule: Deoxyribose in the case of DNA.

* A phosphate group: A phosphorus atom bound to four oxygen atoms.

* A nitrogenous base: There are four types of nitrogenous bases in DNA: adenine (A), guanine (G), cytosine (C), and thymine (T).

How nucleotides join to form DNA:

* Nucleotides link together to form long chains called polynucleotides.

* The phosphate group of one nucleotide binds to the sugar molecule of the next nucleotide, forming a phosphodiester bond.

* This creates a sugar-phosphate backbone that runs along the length of the DNA molecule.

* The nitrogenous bases stick out from the backbone, forming the "rungs" of the DNA ladder.

* Base pairing: Adenine (A) always pairs with thymine (T), and guanine (G) always pairs with cytosine (C). This specific base pairing is crucial for DNA replication and protein synthesis.

So, to summarize, nucleotides are the fundamental units that join together through phosphodiester bonds to create the complex structure of DNA.