Kary B. Mullis: The Genius Behind the Polymerase Chain Reaction

Kary Mullis was an American biochemist who was awarded the Nobel Prize in Chemistry in 1993 for his invention of the polymerase chain reaction (PCR). This technique allows for the copying of a specific stretch of DNA billions of times in just a few hours. Mullis was born in Lenoir, North Carolina on December 28, 1944, and passed away on August 7, 2019, in Newport Beach, California.

• Born: Kary Banks Mullis · December 28, 1944 · Lenoir, North Carolina, U.S.
• Died: August 7, 2019 (aged 74) · Newport Beach, California, U.S.
• Known for: Invention of polymerase chain reaction
• Fields: Molecular biology

In This Article:

Kary B. Mullis: The Visionary Behind the Polymerase Chain Reaction (PCR)

Kary Banks Mullis, an American biochemist, forever changed the landscape of molecular biology with his groundbreaking invention of the polymerase chain reaction (PCR). This transformative technique allows scientists to amplify specific DNA sequences, making it possible to create billions of copies from a small sample in just a few hours. The impact of PCR has been far-reaching, influencing fields as diverse as genetics, medicine, and forensic science. For his revolutionary discovery, Mullis was awarded the Nobel Prize in Chemistry in 1993.

PCR’s ability to replicate DNA quickly and accurately has made it an indispensable tool in scientific research, enabling advancements in everything from disease diagnosis to criminal investigations. Mullis’s unique combination of curiosity, creativity, and unconventional thinking led to one of the most significant breakthroughs in modern science.

Early Life and Education of Kary Mullis

Kary Mullis was born on December 28, 1944, in Lenoir, North Carolina. From an early age, Mullis demonstrated an inquisitive nature and a passion for science. He attended the Georgia Institute of Technology, where he earned a B.S. in Chemistry in 1966. His thirst for knowledge led him to pursue graduate studies at the University of California, Berkeley, where he earned a Ph.D. in biochemistry in 1972. At Berkeley, Mullis thrived in the intellectually stimulating environment, working under renowned scientists and developing the critical thinking skills that would later fuel his groundbreaking work.

The Genesis of PCR: A Serendipitous Idea

In 1979, Mullis joined Cetus Corporation, a biotechnology firm focused on cutting-edge research. It was during his time at Cetus that Mullis developed the concept of PCR, a method that allows for the exponential amplification of specific DNA sequences. The idea came to him during a late-night drive in 1983, a flash of insight that revolutionized molecular biology. Prior to PCR, replicating DNA required laborious methods, and large amounts of DNA were needed for analysis. Mullis’s innovation eliminated these hurdles, allowing researchers to amplify minute amounts of DNA rapidly and with precision.

How PCR Works: The Science Behind the Innovation

PCR mimics the natural process of DNA replication but in a controlled laboratory environment. The technique requires three key steps:

1. Denaturation: The double-stranded DNA is heated to around 95°C to break the hydrogen bonds between the two strands, separating them.
2. Annealing: The temperature is lowered to allow short sequences of synthetic DNA, known as primers, to bind (or anneal) to specific target sequences on the separated DNA strands.
3. Extension: The temperature is then raised to around 72°C, enabling the enzyme Taq polymerase (extracted from the heat-resistant bacterium Thermus aquaticus) to synthesize new strands of DNA by adding nucleotides to the primers.

This cycle is repeated multiple times, with each cycle doubling the amount of DNA, resulting in exponential amplification. PCR’s efficiency and sensitivity make it ideal for analyzing trace amounts of DNA in fields like forensic science, where even a single molecule of DNA can be amplified into billions of copies.

Overcoming Challenges: Mullis’s Key Insight

Although the idea of amplifying DNA was not entirely new, previous attempts had encountered a major problem: the enzyme DNA polymerase used in the process would degrade at the high temperatures required for DNA denaturation. Mullis’s critical insight was to use a special heat-stable polymerase from the bacterium Thermus aquaticus, commonly known as Taq polymerase. This enzyme could withstand the high temperatures necessary for DNA denaturation, allowing the PCR process to proceed without needing to add new enzymes after each cycle. This breakthrough made PCR practical and scalable, transforming the way scientists conduct DNA analysis.

PCR’s Profound Impact on Science and Medicine

The implications of PCR were immense and immediate. Suddenly, researchers could amplify specific DNA sequences from a tiny sample, opening the door to numerous scientific advances:

• Genetic Research: PCR became a foundational tool in genomics, allowing scientists to analyze genes, identify mutations, and map the human genome.
• Forensic Science: PCR revolutionized criminal investigations by enabling the analysis of minute DNA samples from crime scenes. DNA typing became faster and more reliable, leading to the conviction of perpetrators and the exoneration of the wrongfully accused.
• Medicine: PCR is used to diagnose genetic disorders, identify pathogens, and track the spread of infectious diseases. It has been critical in fields like cancer research, where detecting genetic mutations can guide personalized treatments.
• COVID-19 Testing: During the COVID-19 pandemic, PCR became the gold standard for testing. By detecting the genetic material of the virus, PCR tests allowed for early, accurate diagnosis, playing a crucial role in controlling the spread of the virus.

Forensic Applications of PCR: A Game-Changer

PCR has had an especially profound effect on forensic science. Prior to its invention, DNA analysis required large samples of biological material, often limiting its usefulness in investigations. With PCR, forensic scientists can now analyze even trace amounts of DNA—such as a single hair, a drop of blood, or a few skin cells. PCR’s speed and accuracy have revolutionized DNA profiling, making it a powerful tool in solving crimes, identifying victims, and proving paternity.

Notably, PCR played a critical role in many high-profile criminal cases, where DNA evidence became a linchpin in courtrooms. Its ability to provide definitive genetic matches has improved the justice system, both by securing convictions and overturning wrongful ones.

Recognition and Awards

Kary Mullis’s contribution to science earned him international acclaim. In 1993, he was awarded the Nobel Prize in Chemistry for the invention of PCR, sharing the award with Michael Smith, who was recognized for his contributions to site-directed mutagenesis. Mullis’s other notable honors include:

• Japan Prize
• National Biotechnology Award
• Gairdner Award
• Thomas A. Edison Award
• California Scientist of the Year
• Induction into the National Inventors Hall of Fame

Mullis was known not only for his scientific achievements but also for his colorful personality. He often challenged conventional thinking and was outspoken on a range of issues, sometimes courting controversy. His eccentricity and brilliance made him a memorable figure in the scientific community.

Legacy: Mullis’s Lasting Impact on Science

Kary Mullis passed away on August 7, 2019, in Newport Beach, California, at the age of 74. His legacy, however, continues to thrive through PCR, which remains a cornerstone of molecular biology, genetics, and forensic science. The technique he pioneered has paved the way for countless scientific discoveries and technological advancements.

Today, PCR is used in laboratories around the world for applications that Mullis could not have imagined when he first conceived the idea in 1983. From solving crimes to diagnosing diseases, PCR has become an indispensable tool in the arsenal of modern science.

How did Kary Mullis’s invention of PCR change the landscape of forensic science and molecular biology?