Nucleic Acid Sequence
Nucleic acids consist of a chain of linked unites called necleotides. Each nucleotide consists of three subunits: a phosphate group and a sugar (ribose in hte 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.
In biological systems, nucleic acids (DNA article from Wikipedia) contain inofmration which is used by a living cell to construct specific proteins. The sequence of nucleobases on a nucleic 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