Kary Banks Mullis studied the chemical processes within living organisms, known as biochemistry, during the late twentieth century in the US. He helped invent the polymerase chain reaction, or PCR. PCR is a technique used in laboratories that makes millions of copies of a specific segment of DNA, the molecule that holds the genetic instructions in every living organism. In the twenty-first century, PCR is widely used for such applications as identifying diseases, solving crimes, researching genes, growing better crops, and monitoring the environment. Despite some debates about merited recognition, Mullis received the 1993 Nobel Prize in Chemistry for inventing the PCR method. Later in his career, he took controversial stances against the accepted science of HIV and climate change. Through his work on PCR, Mullis helped to facilitate advances in numerous fields of research that rely on molecular biology, which is the study of the basic chemical and physical processes that structure living systems.

Polymerase chain reaction, or PCR, is a technique that scientists use to rapidly make millions of copies of deoxyribonucleic acid, or DNA, which is the genetic material found inside every living organism. Kary Mullis, who shared the 1993 Nobel Prize in Chemistry for his contributions to PCR, developed the idea for its underlying biochemical mechanism in the early 1980s while working at Cetus Corporation, a company in Emeryville, California, that used biology to create tools for medical treatments, including cancer. Over the next several years, Mullis and his Cetus colleagues developed the technology, publishing the first study to reference PCR in the journal Science in 1985. Cetus scientists further enhanced PCR by adding Taq polymerase, an enzyme that helps copy DNA and remains stable at high temperatures. Prior to the development of PCR, researchers used slow, difficult methods to study small amounts of DNA. PCR facilitated the rapid and affordable amplification of DNA, helping with tasks like diagnosing diseases, solving crimes, and testing food and water for bacterial contamination.