Last week we did a week-long unit on ecosystem dynamics and evolution, which included the usual activities: looking at pond water microbes under the microscope, DNA extraction, walks in the woods (saw a snake!), predator-prey modeling, and so forth.
(Incidentally, we did our modeling in NetLogo, which is a terrific tool for teaching multi-agent modeling; I should do a separate post about this!)
Most this was run-of-the-mill science, and not too worthy of report, except for one interesting event.
DNA extraction from strawberries — using dish soap, salt, and alcohol — is about the most fun lab activity you can do in your kitchen! Here’s one of many all-the-same protocols you can find online. Unfortunately, all you get at the end is a huge clump of what is supposedly DNA. Since we were doing microscope work earlier in the week, I decided to try to visualize the DNA. My microscope goes up to about 470x (without oil), and since you need an electron microscope to see the helical structure at all, I figured that we wouldn’t see much in my light microscope.
However, when I was working in the lab we used a simple technique, called molecular combing, to stretch out the chromosomes in order to count them and get their sizes. I didn’t think that this would do anything useful in our kitchen, as you generally have to attach fluorescent markers to see the chromosomes in the lab, but I decided to give it a try anyhow.
Amazingly, just using the cover slip of the microscope slide to “comb” the strawberry DNA extract, we were able to visualize … well, I have no idea what this is:
They sure do look like helical structures of some sort. I’m guessing that these aren’t DNA, unless strawberry DNA are humongous! Rather, they are probably some sort of connective tissue from the strawberries. But for our first try at visualizing something DNA-like, it was pretty exciting. (I didn’t let on to Leo that these are almost certainly NOT DNA!)
Incidentally, this “photomicrograph” was taken by just putting my iPhone up to the eyepiece of the microscope. It took a few tries, but I’m slightly amazed that it worked at all!