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.