Polymerase chain reaction (PCR) is a method of molecular biology that allows you to detect small amounts of deoxyribonucleic acid (DNA) in biological material, more precisely, certain fragments of it, and multiply them many times over. 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 a laboratory. DNA reproduction may not begin in any region of the molecule, but only in regions with a certain nucleotide sequence - 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., corresponding) to the starting regions of the sample's DNA.
Of course, in order to create primers, scientists must study the nucleotide sequence of the nucleic acid involved in the technique. It is these DNA probes that provide the specificity of the reaction and its initiation. The polymerase chain reaction will not go if at least one molecule of the desired DNA is not found in the sample. In general, the above primers, a set of nucleotides, a heat-resistant DNA polymerase are necessary for the reaction to take place. The latter is an enzyme - a catalyst for the synthesis of new nucleic acid molecules based on the sample. All these substances, including the biological material in which it is necessary to detect DNA, are combined into a reaction mixture (solution). It is placed in a special thermostat that performs very rapid heating and cooling for a given time - a cycle. Usually there are 30-50.
How does this reaction work
Its essence lies in the fact that during one cycle the primers are attached to the desired sections of DNA, after which it is doubled under the action of the enzyme. Based on the resulting DNA strands, new and new identical fragments of the molecule are synthesized in subsequent cycles.
The polymerase chain reaction proceeds sequentially, its following stages are distinguished. The first is characterized by a doubling of the amount of product during each heating and cooling cycle. In the second stage, the reaction slows down, as the enzyme is damaged and also loses activity. In addition, the reserves of nucleotides and primers are depleted. At the last stage - a plateau - products no longer accumulate,because the reagents are out.
Where it is used
Undoubtedly, the polymerase chain reaction finds the widest application in medicine and science. It is used in general and private biology, veterinary medicine, pharmacy and even ecology. Moreover, in the latter they do this to monitor the quality of food products and environmental objects. The polymerase chain reaction is actively used in forensic practice to confirm paternity and identify a person. In forensics, as well as in paleontology, this technique is often the only way out, since usually very little DNA is available for research. Of course, the method has found a very wide application in practical medicine. It is needed in such areas as genetics, infectious diseases and oncological diseases.
