BOX 5.1Overcoming Scientific Roadblocks: PCR and Penicillin

The dramatic explosion of research and application that can follow from overcoming a scientific roadblock is demonstrated by two well-known examples from 20th-century life sciences.

Polymerase Chain Reaction (PCR)

Scientists knew that the primary genetic material of life was encoded in DNA but were limited in their abilities to analyze and manipulate specific genes because any particular sample contained such a small quantity mixed among other genetic material. In the 1980s, Dr. Kary Mullis described a technique to amplify a specific DNA sequence multiple fold. PCR exploits key aspects of DNA replication: double-stranded pieces of DNA are separated at high temperature; short DNA primers flanking and complementary to the target DNA sequence are annealed at lower temperature; and the enzyme DNA polymerase synthesizes new DNA to copy the target sequence. These cycles of heating and cooling are repeated, doubling the amount of target DNA each time. Starting from a single DNA copy, 32 cycles of PCR will yield more than 1 million copies of the target sequence. This technique revolutionized molecular biology and paved the way for a subsequent explosion in genetic research. The ability to amplify individual DNA sequences greatly expanded the ability to detect and analyze gene mutations, to associate genetic changes with particular diseases, and to enable medical diagnosis and genetic screening. PCR is one of the fundamental techniques that underpin modern biotechnology.


In 1928, Alexander Fleming at St. Mary’s Hospital in London identified a mold from the genus Penicillium on a culture plate of Staphylococcus bacteria he had left on a lab bench. A substance released by the mold had killed the bacteria, leaving a plaque—he subsequently named this substance penicillin and tested its efficacy against various types of bacteria. Early studies on the potential disease-fighting properties of penicillin were severely hampered by difficulty isolating and producing it. In the late 1930s, Ernst Chain, Howard Florey, and Norman Heatley at the University of Oxford became interested in penicillin, studying its chemistry and working in collaboration with Andrew Moyer of the U.S. Department of Agriculture’s (USDA’s) Northern Regional Research Laboratory to significantly improve the ability to purify and produce it in larger quantities. The subsequent medical studies this enabled established penicillin as a “miracle drug” that dramatically improved treatment for bacterial diseases and started the age of antibiotic therapeutics. The discovery of penicillin also highlights the long-standing interdisciplinary nature of life sciences research—the combination of Fleming’s biological observations with the Oxford and USDA researchers’ chemical and production work, as well as the determination by Dorothy Hodgkin of penicillin’s molecular structure using x-ray crystallography, brought penicillin to the point that it could feasibly be tested and used clinically and helped facilitate the development of new antibiotics.

From: 5, Monitoring and Assessing Trends in Science and Technology

Cover of Life Sciences and Related Fields
Life Sciences and Related Fields: Trends Relevant to the Biological Weapons Convention.
National Research Council (US) Committee on Trends in Science and Technology Relevant to the Biological Weapons Convention: An International Workshop.
Washington (DC): National Academies Press (US); 2011.
Copyright © 2011, National Academy of Sciences.

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