A<unk>  or genetic<unk>  is a succession of letters representing the primary structure of a real or hypothetical<unk>  molecule or strand, with the capacity to carry information.
The possible letters are A, C, G, and T, representing the four nucleotide subunits of a<unk>  strand - adenine, cytosine, guanine, thymine bases covalently linked to phospho-backbone. In the typical case, the<unk> s are printed abutting one another without gaps, as in the<unk>  AAAGTCTGAC, going from 5' to 3' from left to right. A succession of any number of nucleotides greater than four is liable to be called a<unk> . With regard to its biological function, which may depend on context, a<unk>  may be sense or anti-sense, and either coding or noncoding.<unk> s can also contain "junk<unk> ."<unk> s can be derived from the biological raw material through a process called<unk> ng.
In some special cases, letters besides A, T, C, and G are present in a<unk> . These letters represent ambiguity. Of all the molecules sampled, there is more than one kind of nucleotide at that position. The rules of the International Union of Pure and Applied Chemistry (IUPAC) are as follows:
DNA sequence
Molecular mass
Open reading frame
Transcriptome
Peptide sequence
DNA supercoil
Gene expression
Spin quantum number