starts with only a single copy of a fragment. After one cycle of PCR two copies of the desired fragment exist. After two cycles four copies exist, and after three cycles eight copies exist. Four cycles make 16 copies. The increase in copy number is not linear, but rather geometric. Finally, after approximately 30 cycles, over a billion copies of a particular DNA segment will exist in the reaction.
Mullis had one serious problem to overcome. At 95 °C almost all cellular material denatures, destroying the needed polymerase in the PCR reaction. In the original PCR design, fresh polymerase had to be added after each cycle. By 1988, however, the cycle was modified by the addition of a DNA polymerase from the bacterium Thermus aquaticus, which normally thrives in and around deep‐water thermal vents and easily resists the 95 °C melting temperature in the PCR cycles. The cycle could thus run continuously without adding fresh polymerase by starting it at 94 °C (denaturing the DNA strands), lowering it to 45–65 °C (to anneal the primers), and then raising it to 72 °C (to activate the T. aquaticus, or Taq, polymerase). (39)
The molecular revolution was just over 30 years old by the mid‐1980s. Although so much had been accomplished since Watson and Crick’s groundbreaking discovery in 1953, the broader application of genetics was limited by the then‐current state of technology. Molecular biologists had established the basic physical and chemical rules of heredity, providing the biochemical tools to answer Schrodinger’s question What is Life? From Sanger’s basic sequencing tools, to the cracking of the genetic code, to the development of PCR, technologies were developed that brought science closer to answering Schrodinger’s question. But even with these tools scientists were only barely able to apply knowledge of cellular “life” to basic medical challenges. The genetics of sickle‐cell anemia, for example, have been understood for more than 50 years yet there is still no cure for this disease. The proposal to sequence the human genome in 1985 was an attempt to provide biology with something akin to chemistry’s periodic table. Such a catalog of the human genome, scientists hoped, would provide a foundation for improving our understanding of the relationship between genetics and human disease, and be a way to begin to apply nearly a century of work in genetics to health care. Much as Schrodinger’s question prompted a generation of scientists to investigate and uncover the molecular mechanisms of heredity, the sequencing of the human genome inspired scientists at the dawn of the twenty‐first century to develop a more precise and richer understanding of how our genomes work.
REFERENCES
1 1. Erwin Schrodinger. 1992. What is Life: The Physical Aspect of the Living Cell. New York: Cambridge University Press, p.5.
2 2. Schrodinger, 1992, p.6.
3 3. Schrodinger, 1992, p.3.
4 4. Schrodinger, 1992, p.5.
5 5. Horace Freeland Judson. 1996. The Eighth Day of Creation: Makers of the Revolution in Biology. Cold Spring Harbor, NY: Cold Spring Harbor Laboratory Press, pp.29, 87–88; James D. Watson and Andrew Berry. 2003. DNA: The Secret of Life. New York: Alfred A. Knopf, pp. 35–36.
6 6. Stephen Jay Gould. 1995. “What is Life?” As a Problem in History,” What is Life? The Next Fifty Years: Speculations on the Future of Biology. Michael P. Murphy and Luke A.J. O’Neill, eds. Cambridge: Cambridge University Press, p.26.
7 7. Frederick Sanger. 1945. “The Free Amino Groups of Insulin,” Biochemical Journal 39: p.507.
8 8. Frederick Sanger. 2003. “What You Need to Know About … Phenylketonuria,” Nursing Times 99: p.26.
9 9. Frederick Sanger. 1959. “Chemistry of Insulin,” Science 129: oo.1340–1344; Frederick Sanger. 1988, “Sequences, Sequences, Sequences,” Annual Review of Biochemistry 57: pp.1–28.
10 10. Sanger, 1959, pp.1340–1344.
11 11. Judson, 1996, p.88.
12 12. Sanger, 1959, pp.1340–1344.
13 13. Alok Jha. 2013. “DNA Pioneer Frederick Sanger Dies Aged 95,” The Guardian (November 20): p.14.
14 14. Judson, 1996, pp.256–266.
15 15. Judson, 1996, p.470.
16 16. Michael Morange. 1988. A History of Molecular Biology. Cambridge, MA: Harvard University Press, p.135; Marshall W. Nirenberg and Johann H. Matthaei. 1961. “The Dependence of Cell‐Free Protein Synthesis in E. coli upon Naturally Occurring or Synthetic Polyribonucleotides,” Proceedings of the National Academy of Sciences USA 47: pp.1588–1602.
17 17. Judson, 1996, p.298.
18 18. Horace Freeland Judson. 1992. “A History of the Science and Technology Behind Gene Mapping and Sequencing,” in The Code of Codes: Scientific and Social Issues in the Human Genome Project. Daniel J. Kevles and Leroy Hood, eds. Cambridge, MA: Harvard University Press, p. 59.
19 19. Sydney Brenner, Francois Jacob, and Matthew Messelson. 1961. “An Unstable Intermediary Carrying Information from Genes to Ribosomes for Protein Synthesis,” Nature 190: pp.576–581; Francoise Jacob and Jacque Monod. 1961. “Genetic Regulatory Mechanisms in the Biosynthesis of Proteins,” Journal of Molecular Biology 3: pp.318–356.
20 20. Morange, 1998, p.22.
21 21. George W. Beadle. 1977. “Genes and Chemical Reactions in Neurospora,” in Nobel Lectures in Molecular Biology, 1933–1975. New York: Elsevier, pp. 51–63; Tonse N.K. Raju. 1999. “The Nobel Chronicles,” The Lancet 353: p.2082.
22 22. Arthur Kornberg. 1989. For the Love of Enzymes: The Odyssey of a Biochemist. Cambridge, MA: Harvard University Press, p.121.
23 23. Kornberg, 1989, pp.147–154.
24 24. Morange, 1998, pp.236–237.
25 25. Kornberg, 1989, pp.217–220, 240–268.
26 26. Edward Southern. 1975. “Detection of Specific Sequences Among DNA Fragments Separated by Gel Electrophoresis,” Journal of Molecular Biology 98: pp.503–517.
27 27. David C. Darling and Paul M. Brickell. 1994. Nucleic Acid Blotting: The Basics. New York: Oxford University Press.
28 28. Stanley Cohen et al. 1973. “Constrcution of Biologically Functional Bacterial Plasmids in vitro,” Proceedings of the National Academy of Sciences USA 70: pp.3240–3244.
29 29. Eric Green. 2002. “Sequencing the Human Genome: Elucidating Our Genetic Blueprint,” in The Genomic Revolution: Unveiling the Unity of Life. Michael Yudell and Rob DeSalle eds. Washington, DC: Joseph Henry Press, p.39.
30 30. Robert Cook‐Deegan. 1994. The Gene Wars: Science, Politics, and the Human Genome. New York: W.W. Norton and Company, p. 62.
31 31. Kevin Davies. 2001. Cracking the Genome: Inside the Race to Unlock Human DNA. New York: The Free Press, p.37.
32 32. Frederick Sanger et al. 1977. “DNA Sequencing with Chain‐Terminating Inhibitors,” Proceedings of the National Academy of Sciences USA 74: pp.5463–5467.
33 33. Green, 2002, p.40; Sanger, 1988, pp.1–28.
34 34. Cook‐Deegan, 1994, p.62.
35 35. Morange, 1998, p.205.
36 36. International Human Genome Sequencing Consortium. 2001. “Initial Sequencing
