We've also looked at this DNA synthesis issue in a sort of parallel way. What we used is P-33 phosphate. Again, you just can't buy phosphate in purple or green, so we used the radioactive tracer here. We mixed it with a sample in the bag, put it back in the stream so we don't have radiation going down these streams. It's all done, of course, with permits and so on. We incubate them and after a certain amount of time we put them in the dry ice, we bring them back and then what we do is we purify the DNA in the labs and we look for the amount of radiation that's been incorporated into the DNA. So we get some kind of a specific activity. If you've never heard of this before, don't be surprised, this is my own little invention here but I think it's kind of a clever way to actually measure DNA synthesis out in the field.

Back to P-33 and DNA, what happens at the molecular level is when I give them this radioactive phosphate, them meaning these algae, they're taking it and they're having to add it on to ADP and then the phosphate goes on this glucose and new nucleotides are made just incorporating this DNA. I will have to admit that I stupidly, when I started doing these experiments a bit naively, wasn't thinking and I said, well, gosh, if you add phosphates you just tack it on to the end of the ADP and that gets right to the phosphate backbone. No. Dumb me. Of course not. Phosphate on nucleotides that actually get some phosphate into the backbone of DNA is the phosphate first position.

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