The story behind the PCR (Polymerase Chain Reaction)

PCR has often been equated with the discovery of the Internet which seemed rather controversial as one impacts the whole world and other limits to the scientific community. However, their implications and use have been equally valued in both quality and quantity in the last 40 years. Human life is unimaginable without the internet and it is preposterous to say that any biological research now can work without a part of PCR in it. PCR is the cornerstone behind the Human Genome project and every molecular biology works. It’s quite astonishing to know that the discovery was made just 40 years ago.

PCR is a technique, not a machine.

The story of PCR starts with the isolation of Taq DNA Polymerase from Thermus aquaticus in 1976 by a surprised microbiologist, Thomas Brock, who found them living at temperatures of over 70 degrees Centigrade in hot springs at the Yellowstone National Park. This meant that the molecular biologists had their hands upon the thermally stable enzyme and they did not have to add enzyme at every cycle. Back in the days, PCR reactions had to be reset to as many as 40 times for over 5 hours in a hot water bath which was no fun. Taq enzyme made our lives better and easier in so many ways.

The use of this Taq enzyme was not much widespread until 1988 when Kary Mullis and the Cetus Corporation Emeryville, California made the enzyme commercially available. Driving a Honda Civic on Highway 128 from San Francisco to Mendocino, in the spring of 1983, Dr. Kary Mullis conceived an idea in his head that led to the successful development of PCR using which we now can produce millions of copies of DNA from a scarce quantity in a test-tube. He earned a $10,000 bonus from the company he worked for and Cetus Corporation got the patent which later they sold to Roche for $300 million. Kary Mullis was awarded Nobel Prize in 1993 for the work he did in the 1980s.

PCR; it simply is an amplifier. It amplifies a DNA into far too many millions of same copies. What’s needed for the process? A test-tube to hold a large loose collection of nucleotides, the original DNA that we need to copy, a short DNA segment called primers which attaches to the DNA we need to copy and fix the starting point for the synthesis and, Taq polymerase enzyme that locks the loose nucleotides into the sequence between the primers. 

In the thermal cycler, the test-tube is heated which unzips the DNA strands, the temperature gets lowered which allows the complementary pairing of primers to the open strand of DNA, and at the same time enzyme loads the free nucleotides into the DNA forming a double-stranded structure in between the primers. The process now cycles repeatedly for 30-40 times and the number of DNA increases geometrically. After 30-40 cycles, a single DNA gets multiplied to hundreds of millions of same copies.

PCR is invaluable in far too many applications. Anything that involves DNA/RNA has PCR there with it. It is the major breakthrough in modern molecular biology. Apart from research works, it can be used in diagnosing the diseases, detection of bacteria, viruses in the human body, detection of mutation in a child before birth, forensics, identification of archaeological evidence, etc. With modern additives, PCR has been getting better and better each day. The accuracy in the copy and reliability of the data generated through the addition of robust and cutting edge technology in PCR is leading towards making it a limitation free technology.

Binod G C

I'm Binod G C (MSc), a PhD candidate in cell and molecular biology who works as a biology educator and enjoys scientific blogging. My proclivity for blogging is intended to make notes and study materials more accessible to students.

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