Posted on March 23, 2008 - by MG
Every so often I get all nostalgic for molecular biology. Ah, they were good days, so much work to do that you hardly had time to think about anything but science.
I found some videos on YouTube which made me smile. This has got nothing to do with Joshua Files, btw, but if you’ve half an interest in science geek humour, and the nostalgic musings of a former scientist then read on…
Here’s the PCR song. It’s from BIO-RAD, the manufacturer of the thermal recycling machine which makes the Polymerase Chain Reaction possible (at least optimal). Lucky BioRad, they had a bright employee named Kary Mullis who when faced with the dilemma that piqued many scientists in the 1980s, didn’t stop thinking. No; he took a long drive up to Marin County (or from…) and thought long and hard about it.
This was the dilemma: We were all using purified enzymes like DNA polymerase to amplify DNA ‘in vitro’ (as in, not in a cell but in a test-tube), but only on a small scale. We weren’t making enough DNA to use in DNA subcloning work or enough to see on a gel with the naked eye. It wasn’t possible.
We all knew that DNA can be replicated simply by melting the two strands, using DNA polymerase to fill in each strand. In theory, if you kept repeating the process 1 molecule would become 2, then 4, 8,16,32,64 etc. But the process of melting the DNA each time would destroy the enzyme. And it was a big hassle to keep swapping the DNA from water baths to ice baths to cycle the process of melting/annealing.
And that’s where most of us stopped thinking.
Kay Mullis, however, remembered that some bacteria exist at high temperatures (e.g. near volcanic vents under the sea), and have heat-stable enzymes. If he could use the DNA polymerase from such a bacteria, it should be possible to invent a machine that would heat-and-cool tubes for the optimum times so that small amounts of DNA could be melted and annealed 20,30,40 times.
And that would seriously amplify the molecules. That would make it possible to eventually detect teeny weeny amounts of DNA.
And so PCR was invented. As an employee Mullis didn’t get rich but he did invent a process that made the lives of all molecular biologists much easier, revolutionised forensic science and paternity suits.
For some reason I only once had a chance to use PCR. In my early days it wasn’t around and later it just wasn’t applicable to what I was researching, until the last month or so. And then I used it to detect a subcloned DNA molecule I’d made the day before. It was the fastest subcloning I ever did and the PCR worked first time, like a dream…and I thought Jeeeez…why wasn’t this around 6 years ago?!