PCR and eccentric genius who invented it

By Prof Kirthi Tennakone
(Email: ktenna@yahoo.co.uk )

Hardly a day passes without the letters, PCR, – the acronym for polymerase chain reaction — being mentioned. To most of us PCR sounds just a test for knowing whether someone has contracted COVID-19 or not.

The polymerase chain reaction is a game changing technique offering diverse and far reaching applications beyond a gold standard for COVID-19 detection.

It is fascinating and entertaining to learn about polymerase chain reaction and its discoverer Kary Mullis, nicknamed untamed genius.

The invention of PCR is intimately connected to our understanding of the cause of biological inheritance. The reason why we have features resembling our parents. A mystery that lead to the discovery of DNA and development of the science of life thereafter. Brief digression into this subject helps to fathom what PCR really means.

Understanding the cause of biological

inheritance and discovery of DNA

Humans have wondered why progeny resemble parents and have some physical and mental traits of the latter. A sprout from a minuscule banyan seed always grows into a gigantus of the same kind but never a tender mustard plant. The ancient Greeks believed that a creature to be born or a plant to germinate subsisted inside the sperm and the seed respectively in their miniature forms. A different idea gained ground later and lasted for more than 2,000 years that physical traits acquired by parents indirectly pass to the offspring. A proponent of this hypothesis in recent times was the French naturalist Lamarck. If Lamarckism were true, amputation of the tails of successive offspring of mice would eventually lead to a generation of tailless rodents. All such experiments failed.

Lamarckism did not confront creationism and intelligent design to the hurt religious establishment. It attracted communists as a way of improving the society to meet ideological aspirations and enhance crop production. The infamous agronomist Lysenko mistrusting proven science attempted to reform Soviet agriculture believing Lamarckian ideals. He probably faked experimental results to justify his thesis and advised famers to abandon use of fertilizers and grow of each crop intensely segregated in order to increase the yield. The result was a famine that starved millions – a good lesson for those who advocate pseudoscience promoting quackeries as remedies for COVID-19 or recommend withdrawal of fertilizer on basis of unreliable claims.

When the world was deluded by Lamarckism, definitive clues as to what really causes inheritance followed from the seminal works two revolutionaries, Charles Darwin and Gregor Mendel.

Darwin in his presentation of the theory of evolution noted that the decedents of a given species, sometimes include one’s with distinct variations in their characteristics, referred to as mutants. If the new qualities acquired by the mutants fits the environment, they survived and continuation of evolution via natural selection led to the emergence of new species.

Another question crucial to understand the cause of inheritance has been how the traits of male and female sexual partners were represented in the offspring? Without resorting to experiment and careful analysis, the conservative stream of biologists continued to believe it should be a blend of the maternal and paternal traits. In late 1890s, the work of the Austrian monk Gregor Mendel, a mathematician and a botanist as well, provided a conflicting answer. In an experiment lasting for eight years Mendel planted different strains peas, cross-pollinated them and germinated the seeds brought forth to see features of the of linage such as the height to which they grew and the colour of flowers. His results did not indicate blending of traits, instead the original attributes appeared in each generation with different probabilities. Crossing tall and dwarf varieties never procreated medium size plants; instead, they were either tall or dwarf. Mendel concluded that traits were passed to the progeny as distinct qualities – what we refer to as genes today.

The work of Darwin and Mendel compounded by subsequent findings, pinpointed the inescapable conclusion that a chemical substance transmitted inheritance. Many believed it should be a protein. In 1942, the prescient Austrian physicist Erwin Schrodinger, famous for the quantum theory, expressed an alternative opinion. He hypothesized that the heredity determining entity, needed to be a molecule capable of encoding information and replication. Aroused by Schrodinger’s proposition, chemists all over the world competitively researched to identify the causative agent. In early 1950s, American biologist Watson and British physicist Crick, showed that the genetic material found in cells of animals and plants was deoxyribonucleic acid DNA – a lengthy molecule constituted basically of two strands of four different repeated subunits. Molecules of DNA encode information using these units as a four letter alphabet.

Cells of every organism contain DNA characteristic to the species and unique to each individual. The order in which millions of these units sequentially are arranged in a helical chain, is analogous to an instruction manual detailing the development of the organism. Short sequences of the four units in the chain represent genes, dictating special instructions, just like a sentence or a paragraph in the manual.

Polymerase chain reaction (PCR) and its uses

PCR is a technique of amplifying million-fold a tiny quantity of DNA representing a sequence of interest in minutes so that it could be detected even in minutest quantities – justifying the use of the term chain reaction with polymerase as the catalyst ensuing the reaction. In the analogy of DNA to an instruction manual, PCR would be like inserting a book mark to fix a certain page and copying that page many times.

In finest detail DNA is unique to each individual, whether it is a human or a bacterium. The difference between DNAs of individuals in a given species is minuscule. Yet, the identity of a person can be established from DNA in the smear of saliva over a stamp by PCR. Again just like finding a needle in a hay stack, minute quantities of a specific type of DNA in a sample containing excessive quantities of DNAs from background sources, can be selectively ascertained by running a PCR. The technique finds wide range of applications in medical diagnostics, forensics and criminology, archaeology and paleontology, phylogenetics, cloning, gene editing etc.

How is PCR detecting corona virus?

The genetic material of the corona virus is RNA – a single strand of DNA. The test first converts RNA into DNA making it double stranded and then selectively amplify a fragment of DNA covering a specific sequence using special reagents. The amplification enables detection by a screening system. Test is extremely sensitive; in fact, too sensitive, responding to even the dead fragments of the virus.

The impact of PCR on forensics and criminology is unprecedented. The technique has enabled not only identification of criminals but also the exoneration of innocent. A man on death row for eight years has been released and compensated as PCR became available.

Kary Mullis: The man who discovered PCR

Kary Mullis born in Southern United States 1944 was exceptional and radical. As a high schooler he meddled with chemicals at home and created an ingenious technique for making rocket fuels. His homemade rockets propelled miles into the sky frightening pilots maneuvering airplanes to land. Having earned a bachelor’s degree in chemistry from Georgia Institute of Technology he moved to University of California, Berkeley to pursue studies towards a doctoral degree in chemistry. A fashionable field of study at that time was chemistry of DNA or molecular biology. Instead of following courses in biochemistry needed for the thesis, he opted for astrophysics, saying he could learn the former discipline talking to colleagues. He wrote an article on a fundamental problem in astrophysics and succeeded getting it printed in the prestigious journal Nature. He was a surfing enthusiast and guitarist.

At the oral examination for qualifying to register as a doctoral candidate, Mullis was found to be unprepared and weak in conventional biochemistry. However, his paper on an astrophysical subject rather than biochemistry saved him from disqualification. The committee decided despite odd behaviour and unpreparedness, the man was talented and granted him approval for registration. Mullis earned a Ph.D. in 1973 and decided to give up research to become a writer and worked in a restaurant. Later, one of his friends persuaded him to a job in a biochemical company, at least to earn a living. There, he worked in a laboratory devoted to DNA chemistry, often quarrelling with coworkers. In early 1980s, he came up with the idea of PCR, but no one took him seriously. The paper he wrote was rejected twice and finally published in a less acclaimed journal. Soon the world acknowledged the utmost significance of his work and Mullis shared 1993 chemistry Nobel Prize. He resorted to eccentric behaviour criticizing the establishment and mainstream thinking, earning reputation as the untamed genius. When he was invited to a high-standing conference on molecular biology, he projected three slides of female nudes, lambasted the way of funding research and vanished! In an interview, Mullis has said Nobel Prize serves as a licence to do things unacceptable.

Kary Mullis, who passed away in 2019, will be remembered as a demarcater of biology into two epochs – before PCR and after PCR. Fortunately, the pandemic is post – PCR. Otherwise the situation would have taken a more deadly and devastating turn.

The invention of PCR stands as a prime example to highlight how fundamental studies motivating creativity, foresight and hard work can pay off unexpectedly. A constant reminder to research and academic institutions to retain this spirit of accommodating the most talented and not the mediocre who entertain trivialities for the shake of survival. The latter even amend (adulterate) the established mandates for fostering advanced studies to suit them. And deceiving the policymaker and general public, stating the amendments (adulterations) were affected to meet national interest (self-interest).

Would a man of the calibre of Kary Mullis be considered for employment or allowed to continue in our institutions? Will a committee here act with the same altruism and consideration as the one that endorsed the candidature of Kary Mullis?