The man who won the 1993 NOBEL PRIZE in chemistry for inventing the Polymerase Chain Reaction (PCR) died on 7 th August 2019 in California. His landmark discovery, hailed as one of the most important scientific inventions of the 20th century, revolutionized Biology. In PCR, the Taq polymerase (a heat stable DNA polymerase enzyme capable of operating at 97.5 °C, isolated from the thermophilic bacterium Thermus aquaticus) containing mixture is cycled through sequences of heating and cooling to amplify the target DNA, creating millions of copies of a chosen sequence in a relatively short period of time. This can then be used for medical diagnosis or experimentation such as DNA cloning. PCR has become an indispensable technique in molecular biology ever since its inception. Before PCR, DNA amplification was a cumbersome, herculean task, took weeks before it had to be generated in bacteria. PCR technique opened a new world of possibilitiesa discovery that gave scientists the ability to study DNA from ancient samples such as a 40,000-year-old frozen mammoth and helped investigators worldwide to perform DNA fingerprinting analysis to convict or exonerate crime suspects. In the early 1980s, Dr. Mullis was at the biotech company Cetus Corporation, San Francisco, working on the application of synthetic DNAs to biotechnology. There, one night while driving with his girlfriend, an idea struck his head, he could use a pair of primers (a short nucleic acid sequence that provides a starting point for DNA synthesis) to bracket the desired DNA sequence and to copy it using a DNA polymerase. This, coupled with several rounds of thermal cycling, would allow the rapid amplification of any DNA segment- thus was born the technique of PCR. In PCR, target DNA is exposed to repeated cycles of heating and cooling to facilitate denaturation, annealing, and extension (the three basic steps of PCR). Denaturation involves separation of double stranded DNA to single stranded DNA. Annealing helps in attaching primers to target DNA sequence. Extension process involves the creation of new strands of DNA using DNA Polymerase. PCR has innumerous applications in almost all fields of biology, including forensic science, molecular biology and clinical diagnosis of genetic diseases. PCR was extensively used to decode and map the entire human genome sequence as part of the Human Genome Project, which revealed the nucleotide sequence of the entire human DNA and helped to identify and map all the genes in the human genome. Dr. Mullis was born on 28th December 1944 in Lenoir, North Carolina, USA. His interest in chemistry developed quite early when he learned how to chemically synthesize and build solid-state fuel propulsion rockets as a high school student. Mullis, in every sense, was an unconventional scientist and very much defied the stereotype of a “Nobel Prize winner”. After completing his PhD in 1973 in biochemistry at the University of California, Berkeley, he pursued a rather unusual career path; he dropped out of the science world altogether to follow his passion in fiction writing and later worked at a bakery before finding his way back to science via his job at Cetus. Besides PCR, Dr. Mullis also invented a UV sensitive plastic that changes its colour in response to light. He was honoured with several other awards in his life including Japan prize, Canada Gairdner International Award, and John Scott Legacy medal to name a few. Dr. Mullis once said “I think really good science doesn’t come from hard work. The striking advances come from people on the fringes, being playful.”

References

1. “Dancing Naked in the Mind Field” autobiography of Karry Mullis

2. https://www.nytimes.com/2019/08/15/science/kary-b-mullis-dead.html