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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