Polymerase chain reaction, its nature and application

Polymerase chain reaction (PCR) is a method of molecular biology that allows to detect in the biological material small amounts of deoxyribonucleic acid (DNA), more precisely, of certain fragments thereof, and multiply them many times. They are then identified visually by gel electrophoresis. The reaction was developed in 1983 by K. Mullis and is included in the list of outstanding discoveries of recent years.

What are the mechanisms of PCR

The whole technique is based on the ability of nucleic acids to self-replicate, which in this case is carried out artificially in the laboratory. Reproduction of DNA can begin not in any area of the molecule, but only in areas with a certain sequence of nucleotides - starting fragments. In order for the polymerase chain reaction to start, primers (or DNA probes) are needed. These are short fragments of a DNA chain with a given nucleotide sequence. They are complementary (i.e., appropriate) starting regions of the sample DNA.

Of course, in order to create primers, scientists need to study the nucleotide sequence of that nucleic acid that participates in the technique. It is these DNA probes that ensure the specificity of the reaction and its initiation. A polymerase chain reaction does not occur if there is not at least one molecule of the desired DNA in the sample. In general, the above-mentioned primers, a set of nucleotides, a thermally stable DNA polymerase are necessary for carrying out the reaction. The latter is an enzyme, a catalyst for the synthesis of new nucleic acid molecules based on a sample. All these substances, including biological material, in which DNA must be detected, are combined into a reaction mixture (solution). It is placed in a special thermostat, which performs its very rapid heating and cooling in a given time-cycle. Usually there are 30-50 of them.

How does this reaction go?

Its essence lies in the fact that during one cycle primers are attached to the necessary sections of DNA, after which it doubles under the action of the enzyme. Based on the resulting DNA strands in the subsequent cycles, new and new identical fragments of the molecule are synthesized.

The polymerase chain reaction proceeds in sequence, the following stages are isolated. The first is characterized by a doubling of the amount of the product during each heating and cooling cycle. In the second stage, the reaction slows down, because the enzyme is damaged, and also loses its activity. In addition, the stocks of nucleotides and primers are depleted. At the last stage - the plateau - the products no longer accumulate, because the reagents are over.

Where it is used

Undoubtedly, polymerase chain reaction is widely used in medicine and science. It is used in general and private biology, veterinary medicine, pharmacy and even ecology. In the latter, this is done to monitor the quality of food and objects of the external environment. Actively used polymerase chain reaction in forensic practice to confirm paternity and identify a person's personality. In forensic medical examination, as well as in paleontology, this technique is often the only way out, as usually an extremely small amount of DNA is available for research. Undoubtedly, a very wide application of the method found in practical medicine. It is necessary in such areas as genetics, infectious and oncological diseases.