The principle of PCR is biological polymerase chain reaction. The basic principle of PCR technology is similar to the natural replication process of DNA, and its specificity depends on oligonucleotide primers complementary to both ends of the target sequence. PCR is based on the fact that DNA degenerates into single strand at 95℃ in vitro. At low temperature (often about 60℃), the primer and single strand are combined according to the principle of base complementary pairing, and then the temperature is adjusted to the optimum reaction temperature of DNA polymerase (about 72℃), and DNA polymerase synthesizes complementary strand along the direction from phosphoric acid to pentasaccharide (5'-3').

Characteristics of pcr reaction:

1. Strong specificity.

The combination of primer and template and the extension of primer chain follow the principle of base pairing. Because of the fidelity of polymerase synthesis reaction and the high temperature resistance of TaqDNA polymerase, the combination (renaturation) of template and primer in the reaction can be carried out at higher temperature, the specificity of combination is greatly increased, and the amplified target gene fragment can maintain high accuracy. By selecting highly specific and conservative target gene regions, its specificity will be higher.

2. High sensitivity.

The amount of PCR products increases exponentially, and the initial template to be tested can be amplified to the level of μg=-6 according to Pique (pg= 10- 12). A target cell can be detected from 6.5438+0 million cells; In virus detection, the sensitivity of PCR can reach 3 RFU (plaque forming unit); In bacteriology, the lowest detection rate is 3 bacteria.

3. Simple and quick.

Application of thermostable Taq DNA polymerase in PCR reaction. After the reaction solution is added at one time, denaturation-annealing-extension reaction is carried out in DNA amplification solution and water bath pot, and the amplification reaction is generally completed within 2 ~ 4 hours. Amplification products are generally analyzed by electrophoresis, and isotopes are not needed, so there is no radioactive pollution and it is easy to popularize.

4. The purity requirement is low.

There is no need to separate viruses or bacteria from cultured cells, and crude DNA and RNA can be used as amplification templates. It can be directly used for DNA amplification and detection of clinical samples such as blood, body cavity fluid, mouthwash, hair, cells and living tissues.

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