DNA is built from smaller units called nucleotides , and each nucleotide has three parts: a phosphate group, a deoxyribose sugar, and a nitrogenous base (A, T, G, or C). These nucleotides link together to form long strands, which then pair up in a double helix using specific base pairs: adenine with thymine, and cytosine with guanine.

Quick Scoop: Core idea

  • The basic building block of DNA is the nucleotide.
  • Each nucleotide = phosphate + deoxyribose sugar + one base (A, T, G, or C).
  • The order of these bases along the DNA strand is what encodes genetic information.

The three pieces of a nucleotide

  • Phosphate group : Forms part of the sturdy “backbone” and links neighboring nucleotides into a chain.
  • Deoxyribose sugar : The sugar unique to DNA that holds the base and phosphate, giving the molecule its overall structure.
  • Nitrogenous base : The information-carrying part; the four are adenine (A), thymine (T), guanine (G), and cytosine (C).

How they form the double helix

  • Nucleotides connect so that sugar and phosphate repeat along the outside, forming a sugar‑phosphate backbone.
  • Bases stick inward and pair specifically (A–T, C–G), creating “rungs” of a twisted ladder known as the DNA double helix.

Why this matters biologically

  • The sequence of bases along DNA acts like a code that tells cells how to build proteins and run cellular processes.
  • Changes in this base sequence (mutations) can alter traits, diseases, or other characteristics because they change the information stored in the DNA code.

TL;DR: The building blocks of DNA are nucleotides, and each nucleotide is made of a phosphate, a deoxyribose sugar, and one of four bases (A, T, G, C) whose sequence stores genetic information.