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.