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You might have heard about the PCR test during this viral pandemic season. PCR is the recommended laboratory test available to detect the Corona viral infection as much as possible.
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The Polymerase Chain Reaction or PCR is a amplification process which can be used to multiply DNA or RNA. Simply, the PCR is use to produce millions of copies of target piece of DNA from very small sample. Actually PCR itself is not a test, it is a amplification method. But the product of the PCR can be utilized for the diagnosis.
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Any biological sample with RNA or DNA can be used for PCR. AS an example, the Corona virus has RNA in its genome. As we all know the target site for the Corona virus is the human respiratory tract. If we obtain those viral particles from mucous of an infected individual, it contains viral RNAs. Therefore, the health care workers obtain throat and nasal swabs as samples to check for viral RNA using PCR techniques.
Like that we can use any biological sample including animal, microbial or plant materials to perform PCR.
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Usually, the PCR can be performed for both DNA and RNA. In case of RNA, The Reverse Trancriptase PCR (RT-PCR) is used. Here, the complementary DNA (cDNA) is prepared from target RNA template and the resulting fragment is used for the amplification.
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Let’s see  Mainly we need,
- PCR machine/ thermal cycler
- Template DNA( This should be a purified, isolated DNA fragment)
- Primers( A known sequence which is used to identify the particular area of the target fragment to be amplified)
- Taq Polymerase
- Deoxyribo Nucleotide Tri Phosphates( dNTPS of adenine,thymine.guanine and cytocin)
- Nuclease free water and Buffers ( containing MgCl2) and etc.
Mainly there are 3 basic steps in PCR process.
- Denaturation of template strand: First the Ds DNA is breaked and convert it in to single strand. Usually this is done by heating the DNA up to 920C- 940
- Annealing: Here, the primer is sit on the complementary site of the strand for the initiation of DNA synthesis.
- Extention:The Taq Polymerase aids the incorporation of dNTP bases to elongate the DNA strand and extention occurs.
This is a thermo controlled cyclic process and after several cycles, it gives rise to millions to billions of copies of original DNA strand.
So that is it. This is simply about PCR. Yes I know that, now you are in a trouble. What is the fate of this amplified DNA? How can we diagnose a particular infection?
I will explain briefly about it.
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Let’s take microbial infection as an example. Now we have the PCR product obtain from the sample. What we can do is, we need to check our amplified DNA product is similar to microbial DNA/Whether the PCR product matches or complementary with microbial genes. Gel electrophoresis and staining, Sequencing are some of common methods available to do this task. I hope it is clear to you all.
However, the ultimate use of PCR is to generate lots of copies of particular DNA fragment, which is large enough to study in detail through various techniques.
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