Sequencing is the operation of determining the nucleotide sequence of
a given molecule. There are several approaches to sequencing, but
generally, the most successful is based on gel electrophoresis. As mentioned
earlier, the DNA polymerase enzyme catalyzes the replication reaction
of DNA. DNA polymerase extends the chain by adding nucleotides to its end. Current
biotechnology enables synthesis of nucleotides which cause the strand to terminate.
For instance, A* denotes an Adenine molecule which does not allow other
molecules to extend the strand beyond the A* itself. By catalyzing DNA replication in
an environment containing mixtures of normal bases and
synthesized A* bases
instead of only Adenine, it is possible to create DNA strands of different lengths.
By applying gel electrophoresis to these molecules, it is possible to determine
the lengths of all the strands and from it to conclude the location of all Adenines
in the tested DNA strand. In a similar fashion it is possible to locate other
nucleotides (C*,G*,T*) and eventually to fully sequence a whole segment of DNA. Using this
method, sequences of 500-800 nucleotides can be determined. The advanced
sequencing machines nowadays can sequence simultaneously 96 different
sequences of 500-800 nucleotides in a few hours.
The problem that arises from this sequencing technique is the creation of a long DNA chain from the short local sequences. This problem is known as:
