DNA is built from smaller molecules called nucleotides , and each nucleotide has three parts: a phosphate group, a deoxyribose sugar, and a nitrogenous base (A, T, G, or C). When people talk about the “building blocks of DNA,” they usually mean these nucleotides or, more simply, the four bases: adenine (A), thymine (T), guanine (G), and cytosine (C).

Core building blocks

  • The fundamental building block of DNA is the nucleotide, a repeating unit that links together to form each DNA strand.
  • Each nucleotide contains three components: one phosphate group, one deoxyribose sugar, and one nitrogenous base.

The four DNA bases

  • DNA uses four nitrogenous bases: adenine (A), thymine (T), guanine (G), and cytosine (C).
  • These bases pair in a specific way in the double helix: A pairs with T, and G pairs with C, forming the “rungs” of the DNA ladder.

How they form the DNA strand

  • Along each strand, nucleotides connect through their sugar and phosphate groups to create a sugar‑phosphate backbone.
  • The sequence of bases along this backbone encodes genetic information, acting as a molecular code for building proteins and directing cell functions.

TL;DR: The molecules that are the building blocks of DNA are nucleotides—each made of a phosphate, a deoxyribose sugar, and one of four bases: A, T, G, or C.