Sequenced - Definition and Overview

For the sense of "sequencing" used in electronic music, see the music sequencer article.

In genetics and biochemistry, sequencing means to determine the primary structure (or primary sequence) of an unbranched biopolymer. Sequencing results in a symbolic linear depiction known as a sequence which succinctly summarizes much of the atomic-level structure of the sequenced molecule.

In genetics terminology, sequencing is most often restricted to determining the nucleotides of a DNA or RNA strand. Currently, most such sequencing is performed using the chain termination method; however, this can only be used to identify fairly short sequences (around 300-1000 base pairs on ABI machine), and must therefore be used as the basis for more complex techniques, such as chromosome walking and shotgun sequencing.

Other techniques under development, which may offer many benefits over these, include:

• Pyrosequencing
• nanopore sequencing
• GeneEngine

Methods for performing protein sequencing include:

• Edman degradation
• mass spectrometry
• protease digests

Though polysaccharides are also biopolymers, it is not so common to talk of 'sequencing' a polysaccharide, because a symbolic linear depiction cannot capture their tendency to branch and to bond to one another in different ways.

See also

• Genetic code
• Sequence motif

External links

• Information on genome projects, and the data they have produced (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=Genome) at the National Center for Biotechnology Information
• (2005) Genome Sequencing: Using Models to Predict Who's Next. (http://www.plosbiology.org/plosonline/?request=get-document&doi=10.1371%2Fjournal.pbio.0030025) PLoS Biol 3(1): e25.