Field sampling for
Taq and a host of other unique hotwater microbes.
( This is very dangerous and was done under park supervision. Do not attempt!)
DNA. There were a number of factors contributing to Mullis’ creation of the concept, one of which was frustration with the prevailing method of DNA analysis at the time, Southern blotting. It was a process of variable accuracy requiring many steps and substances such as gels, electricity, photosensitive films and— the clincher— radioactivity. Mullis started thinking of another way.
The goal was to take an entire genetic code and detect a target fragment of DNA— one piece of code that might indicate the presence of a certain disease. As for analogy, the endeavor could be likened to listening for a distinct yet barely-audible tone in a cacophonous sea of static. Methods like blotting were analogous to recording the cacophony and sorting out the tones so that a super-sensitive listening device might hear the one being sought. Mullis’ concept was different: Isolate the tone— the DNA fragment— and turn its volume up to a billion( see sidebar).
As early experiments of PCR eventually saw success, its benefits became apparent: PCR promised to be quicker, simpler, more sensitive and convenient— theoretically, the whole process could be done in one test tube, with cycles automated by a machine.
Yet there was one hitch— the rounds of high heat required to split the DNA also degraded the enzyme that catalyzed the chain reaction. They needed something that could take the heat, so to speak— a thermostable enzyme that could withstand the temperature fluctuations. Gelfand had been in PCR meetings at Cetus due to his experience in enzymology, and though making such an enzyme was not quite within his purview, he and colleague Suzanne Stoffel had the tools and the enzymatic know-how. Gelfand also knew where to start, securing thermophilic cultures from the ATCC— including the strain of Taq that Brock had obtained from Yellowstone years prior. After hard work in the lab, Taq’ s efficacy ultimately transformed the process. Says Gelfand,“ It was amazing. Not only did it enable PCR, but it enabled automation. You put everything in a tube, and that’ s it.”
The rest is biotech history, as PCR would come to revolutionize medical diagnostics, support AIDS testing and research, catch criminals, free those wrongly convicted, enable the Human Genome Project( featuring another Triton, J. Craig Venter’ 72, PhD’ 75), connect us with our ancestry and, of course, become the gold standard in detecting COVID-19 on nasal swabs the world over.
Pioneering Process
Polymerase chain reaction( PCR) is a process in which an enzyme causes DNA to reproduce itself:
First, high heat breaks the target DNA into two strands.
Upon cooling, an added enzyme complements both sides to create two new DNA strands.
Many rounds of heating and cooling multiply the DNA strand exponentially: 2 to 4, 4 to 8, into the billions.
But in early PCR, the enzyme derived from E. coli bacteria would degrade from the high heat of many rounds, requiring a new enzyme to be added manually.
Thermus aquaticus, which naturally thrives in the heated pools of Yellowstone, supplied a thermostable enzyme that lasted through the process.
PCR thus became an efficient and reliable means of amplifying DNA for disease testing, forensics, ancestry research and other uses.
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