The Polymerase Chain Reaction
The polymerase chain reaction (PCR) is an approach that is used by scientist to amplify a specific gene of interest. This is a powerful technique that biologist use routinely in order to isolate specific genes or certain DNA fragments when there is prior knowledge known about the sequence that is being amplified. The process of PCR begins in a test tube in which the specific gene of interest is isolated and amplified. We begin this procedure by obtaining a solution that contains the kind of DNA, the primers, the four deoxyribonucleotide triphosphates, and DNA polymerase that is tolerant to heat. A deoxyribonucleotide triphosphate is a single unit of DNA, also known as a monomer and is composed of a nitrogenous base, a deoxyribose sugar, and one phosphate group. The double stranded DNA is first denatured by heat at around 95 degrees Celsius, this causes the DNA to split apart and now the DNA molecules are single stranded. Next, the solution is cooled down at around 50 and 60 degrees and the primers hybridize to their complementary base pairs on the single stranded DNA molecules. Then, the temperature is increased to 72 degree Celsius and the DNA polymerase begins replicating the single-stranded DNA segments. Taq polymerase, which comes for the bacterium Thermus aqucaticus, which grows in thermal vents and makes it resistant to high temperatures of heat. Thus, that is why Taq polymerase is a good polymerase to use because it is able to survive high temperatures that are required for denaturation of the DNA molecules. The Taq polymerase is used to synthesize the first array of complementary strands in the reaction. Next, these two strands are heated again, which causes exposure of four binding sites. After these strands are cooled, the two primers bind to their respective strand at the 3’ ends of the targeted regions on the strands. When temperature rises again, the Taq polymerase synthesizes these four complementary strands. Repeated cycles of denaturation, annealing, and synthesis of the DNA molecules results in an exponentially increase in the amount of segments that are being replicated. Larger quantities of target DNA can be achieved by placing the PCR product into a plasmid. The PCR method is a very common tool used for applications in the biological field. For example, in criminal investigations, investigators are able to amplify segments of human DNA from follicle cells surrounding a single piece of hair.