MicroBiology

DNA Sequencing is a process to determine the precise order of the billions of chemical blocks known as bases. These bases are adenine, thymine, cytosine and guanine and they are abbreviated as A, T, C, and G respectively. They constitute the DNA of the twenty-four different chromosomes present in the human beings. DNA Sequencing contains the heritable genetic data in mitochondria, nuclei, chloroplasts and plasmids. These are responsible to form the base of the developmental programs in all the living organisms.

Thus, determination of the DNA Sequencing is of great help in studying the fundamental biological processes in basic research and in the applied fields like forensic and diagnostic research.  DNA Sequencing has initiated significant acceleration in biological discovery and research. The advent of modern technologies has attained rapid sequencing speed that is influential in the sequencing the large-scale human genome in the Human Genome Project.

For sequencing a piece of DNA, you will require the following: a DNA template containing the DNA that you want to sequence, DNA polymerase enzyme, DNA primer complimentary to the DNA that is being sequenced and four nucleotides. The most common method used for DNA Sequencing is the chain termination method. In this method, modified bases known as dideoxy bases are used. Replication of the DNA piece and incorporation of a dideoxy base in the new chain ceases the replication reaction.

The DNA that is to be sequenced is taken in a single strand form. This single strand acts as template on which the synthesis of a new DNA strand will take place. A nucleotide is included in each reaction, which cannot be extended. This nucleotide acts as a chain terminator. Four reactions, all containing the similar primer and template are set up. The process of incorporation of a new DNA strand takes place randomly as only a small amount of chain terminator is contained in the reaction. Thus, a collection of fragments is generated in each reaction, but all the DNA strands will end up with the same bases (A, C, T or G).

Most of the DNA Sequencing is done by the chain termination method. In the chain termination, method the synthesis of a new DNA strand takes place on a single stranded template. This method generates a set of the DNA molecules that differ in length from one another only by one nucleotide. You can easily recognize the last base in each molecule depending on the size that positions them in an exact order in order to read off the sequence easily.

DNA Sequencing technology is used widely in sequencing the genes and genomes precisely. The more number of times the template is being sequenced, the more accuracy will be achieved. This single-pass and low-fidelity sequencing is of great help in accumulating the sequence information rapidly as well as accurately. Another application where DNA Sequencing is of great use is in resequencing the same type of DNA molecule repeatedly. This is essential in the typing of the single nucleotide polymorphisms.

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