Sequencing

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.

Nucleotide sequencing

In genetics terminology, sequencing is determining the nucleotides of a DNA or RNA strand. Currently, virtually all sequencing is performed using the chain termination method, created by Frederick Sanger. This technique can only be used to identify fairly short sequences at a time (around 300-1000 base pairs on ABI machine), and therefore strategies to have been devised to scale the method up to sequence genes and genome. Two of the mainstream chain termination strategies are chromosome walking and shotgun sequencing. Besides chain termination sequencing, A. Maxam and W.Gilbert developed the chemical modification method in 1977 [1]. However, it is not commonly used due to the greater practicality of the chain termination method.

Other seqeuncing techniques are under development, which may offer many benefits over the conventional methods, include:

• Pyrosequencing
• nanopore sequencing
• GeneEngine

(The problem is, this article doesn't really explain *what it is* to a layman. Less technical terms, and a bit of "why do they do this" would be nice...)

Protein Sequencing

Methods for performing protein sequencing include:

• Edman degradation
• mass spectrometry
• protease digests

Polysaccharide Sequencing

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 at the National Center for Biotechnology Information
• (2005) Genome Sequencing: Using Models to Predict Who's Next. PLoS Biol 3(1): e25.