MicroBiology

DNA Sequencing is the process that determines the exact order of the three billion chemical building blocks known as bases and abbreviated as A, T, C and G. These three billion building blocks are responsible to make up the DNA of the twenty-four different human chromosomes. DNA Sequencing maps are greatly used by the scientists for exploring the human biology as well as many other complex phenomenons related to our body.

The exact order of the bases A, T, C and G are determined in a piece of DNA through DNA Sequencing. In the core, DNA is used as a template for generating a set of fragments differing in length from each other by a single base. These fragments are then separated by size and the bases are recognized at the end, recreating the original sequence of DNA.

The most frequently used method for DNA Sequencing is the dideoxy method or the chain termination method. This method was developed by Fred Sanger. The basics involved in this method is the use of adapted bases known as dideoxy bases. When the DNA piece is replicated and the dideoxy base is integrated in a new chain, the replication reaction stops immediately.

Most of the DNA Sequencing is done by this chain termination method. In this method, a new DNA strand is synthesized on a single stranded template and the chain terminating nucleotide analogues are randomly incorporated. This method leads to the production of a set of DNA molecules that differs in length by a nucleotide. The last base in every molecule can be identified easily due to its unique label. Separation of the DNA molecules as per to their sizes, locates them in a correct order to read off the sequence.

The DNA Sequencing method forms the basis of the automated cycle sequencing reactions. In these reactions, fluorescent dyes are added and a laser, inside the automated DNA Sequencing machine is used for analyzing the DNA fragments that are produced in the process. For sequencing a piece of DNA, you require a short DNA “primer” that is complimentary to the DNA that you wish to sequence, a template DNA i.e. the DNA that you want to sequence, an enzyme known as DNA polymerase and four nucleotides.

DNA Sequencing is a very useful method. The most foreseen application of DNA Sequencing is seen in accurate sequencing of the genomes and genes in your body. Only up to 500-800 bases can be sequenced in one demonstration. So, obviously, the larger DNA molecules along with the genomes should be broken down in small fragments before sequencing them. You will get accuracy only when you sequence each template for a number of times. Low fidelity single pass sequencing is very useful for quick accumulation of the sequence data. Another application where DNA Sequencing is seen is in resequencing the same DNA molecule again and again. This is very important, for instance, in typing of the single nucleotide polymorphisms.

DNA Sequencing is the center of Human Genome Project and it promises to revolutionalize the Biomedical Sciences as well as the treatment of the human disease.