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A nucleotide is the smallest repeating unit in DNA (and RNA).

A single strand of DNA (or RNA) is made from a long chain of nucleotides. The precise order of the nucleotides forms a unique sequences.

Each nucleotide consists of three components:

  • Pentose sugar (deoxyribose in DNA and ribose in RNA) forms the backbone of DNA
  • Phosphate group forms bonds to two sugars
  • Nitrogenous base (A, T, C, G or U) encodes the DNA's instructions

There are four different nitrogenous bases in DNA: Adenosine (A), thymine (T), cytosine (C) and guanine (G). These four bases can be combined in different ways to make unique sequences of DNA.