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What is Polymerase Chain Reaction?
Polymerase chin reaction is a technique of amplifying a single copy of DNA. Thousands and millions of copies of DNA can be produced through this technique having particular sequences. Many primers, enzymes and other conditions are involved in this process. It is often used in DNA fingerprinting, DNA profiling and other tests which are necessary. Its applications range from research to the commercial sector.

Steps Involved in PCR:-
To initiate the polymerase chain reaction it is necessary to have some things like DNA polymerases, Restriction enzymes, a DNA template, primers or short DNA sequences to start the DNA polymerase. Without which the task of making multiple copies cannot be accomplished.

The reaction mixture is heated at the temperature of 94 to 98 degree Celsius for 20 to 30 minutes. It makes the double stranded DNA to melt by breaking the hydrogen bonds that keep the two templates together. Now DNA molecule becomes single stranded.

After the separation of the DNA strands, temperature of the reaction mixture is lowered and is kept at 50 to 65 degree Celsius for 20 to 40 seconds. It causes the annealing of the primers to the single stranded DNA molecules.

In this step, the DNA polymerase makes a complementary strand against each single stranded DNA. Usually Taq polymerase is used for this purpose.

Usually a temperature of 70 to 74 degree Celsius is required for this step to make sure that all the single stranded DNA templates have found their complementary strands.

Uses of PCR:-
The use of polymerase chain reaction is important in many scientific fields like genetics, genetic engineering and molecular biology. In the disciplines like microbiology and molecular biology, it is used for DNA cloning procedures, DNA sequencing, and recombinant DNA technology in the research laboratories. In clinical microbiology, many microbial infections are diagnosed by PCR. Similarly, epidemiological studies also make use of this technique. Field of forensics is another important field which uses PCR for the identification of criminals and to identify the paternity of the child in the court of justice by obtaining only small amount of blood.

Importance of PCR in Biotechnology:-
Polymerase chain reaction is of vital importance in biotechnology. It can be used for the diagnosis of diseases like AIDS, middle ear infection, Lyme disease and tuberculosis. PCR identifies and cultures those microorganisms which are responsible for causing these diseases. This technique also helped a lot during human genome project in the isolation, amplification and sequencing of human genes. Recombinant DNA technology also makes use of the PCR for making multiple copies of transgenes for different applications for example for diagnosing the diseases and for making certain changes in the genome of an organism.

Disadvantages of PCR:-
Like any other reactions, reaction occurring in the PCR also faces some problems. Usually the polymerases used in PCR do not contain the 3’ to 5’ exonuclease activity. Due to this reason, they are not able to correct any errors while incorporating the nucleotides.
Polymerase chain reaction (PCR) is a technique which is used to amplify the number of copies of a specific region of DNA, in order to produce enough DNA to be adequately tested. This technique can be used to identify with a very high-probability, disease-causing viruses and/or bacteria, a deceased person, or a criminal suspect.
In order to use PCR, one must already know the exact sequences which flank (lie on either side of) both ends of a given region of interest in DNA (may be a gene or any sequence). One need not know the DNA sequence in-between. The building-block sequences (nucleotide sequences) of many of the genes and flanking regions of genes of many different organisms are known. We also know that the DNA of different organisms is different (while some genes may be the same, or very similar among organisms, there will always be genes whose DNA sequences differ among different organisms - otherwise, would be the same organism (e.g., same virus, same bacterium, an identical twin; therefore, by identifying the genes which are different, and therefore unique, one can use this information to identify an organism).
PCR (Polymerase Chain Reaction) is a revolutionary method developed by Kary Mullis in the 1980s. PCR is based on using the ability of DNA polymerase to synthesize new strand of DNA complementary to the offered template strand. Because DNA polymerase can add a nucleotide only onto a preexisting 3'-OH group, it needs a primer to which it can add the first nucleotide. This requirement makes it possible to delineate a specific region of template sequence that the researcher wants to amplify. At the end of the PCR reaction, the specific sequence will be accumulated in billions of copies (amplicons).
It’s the law of nature that whenever we grow something, after some time, it results in high returns and prosperity! May it be a small seed which grows as tree and give nutritive fruits, flowers, oxygen, etc or may it be our knowledge! But we as a man never knew that even the amplification (growth) of microscopic (invisible to naked eyes) DNA will give us so much of benefits such that it will bring revolution in the field of science! Yes that’s what happened with Polymerase Chain Reaction technology. PCR technology has not only proved its mettle in bringing the revolution in science but also has once again proved the same law of nature!
Today in modern world of PCR technology, samples of DNA are easily diagnosed for presence of genetic disease mutations. This not only helps in detection of cancers cells but also helps in its effective treatment by specifically identifying the mutant gene. Today PCR technology had helped a lot in Prenatal testing in which DNA can be easily obtained by chorionic villus sampling , amniocentesis or even by detection of rare fetal cells which are in mothers bloodstream and thus these can be easily amplified. PCR is used in tissue typing and has helped in diagnosis of immunological disorders and diseases. Many infectious diseases like HIV, Tuberculosis and endemic are easily diagnosed with the help of PCR. Genetic fingerprinting can easily identify any one person from the entire world population only because of PCR technology.
World is proud of Mullis for his "revolutionary" discovery of PCR. In 1993, Mullis was awarded the Nobel Prize in Chemistry for this excellence which is known as polymerase chain reaction - revolution in science!

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