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Automated Sequences for DNA Sequencing
In manual sequences the DNA fragments are radiolabelled in four different reaction vessels separated on the gel in four different lanes and detected by autoradiography. This is cumbersome and time-consuming making them an invaluable tool to be used in large scale sequencing projects

To overcome this problem, automated DNA sequencing method is developed. This method is a more modified version of dideoxy method. In this process, the dideoxynucleotide that is going to be incorporated in the DNA molecule is not radiolabelled but has a chromogen molecule.

Hence, the fragments that are generated have a colour or a chromogen molecule at the end of the chain. Each dideoxynucleotide is attached by a different fluoromolecule so that the nucleotide at the chain termination can be identified, (Le., all dGTPs have a green colour emitting fluoromolecule attached to it and all dQTPs have a red colour emitting fluoromolecule, etc.)

The other difference is that all the reactions are carried out in the same reaction tube and are run in a single lane in polyacrylamide electrophoresis rather than in four lanes.

As there is no radioactive material in the reaction there is no question of using autoradiography for sequencing. To deduce the sequences, the DNA bands are detected by their fluorescence as they electrophorese past a detector. The molecule or nucleotide at the end can be identified by identifying the flurogen, as we know what flurogen is attached to which nucleotide.

The sequence that is generated in this method will be of complementary strand, as the DNA sequencing proceeds from 5' - 3' end and follows Watson Crick base pairing. Hence the sequence that is obtained is the complementary strand. In automated sequencing, the entire process of detecting and deducing the nascent template DNA sequence is carried out by computers
 

 
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