Nucleaic acid sequence
Nucleic acids consist of a chain of linked units called nucleotides. Each nucleotide consists of three subunits: a phosphate group and a sugar (ribose in the case of RNA, deoxyribose in DNA) make up the backbone of the nucleic acid strand, and attached to the sugar is one of a set of nucleobases.
DNA molecule strand showing double helix structure with deoxyribose and nucleobases.
In biological systems, nucleic acids (https://en.wikipedia.org/wiki/Nucleic_acid) contain information which is used by a living cell to construct specific proteins. The sequence of nucleobases on a nucleaic acid strand is translated by cell machinery into a sequence of amino acids making up a protein strand.
The different nucleobases that make up DNA are