Everyone talks about DNA. And shows those lovely double helix cartoon images of DNA. But when you’re a researcher in a lab, what does DNA actually look like? How in the world do we see it?
- X-Ray crystallography. To be fair, this is an indirect way to see DNA but it is the way that the structure of DNA was determined (as described in our book club book The Double Helix) so it’s worth mentioning. Remember when you were a kid and you made rock candy by hanging a string or stick in water that had a ton of sugar dissolved into it? Well scientists can do the same thing with DNA or proteins – make crystals of them. These crystals are much smaller than the crystals in rock candy. Think microscopic. When molecules are all lined up in the same direction, like they are when they form a crystal, scientists can hit the crystal with X-rays and what bounces around and through the crystal can be detected (this is called a diffraction pattern), measured and transformed to determine the 3D image of the molecule – that double helix structure you see pictures of all the time. This process is called X-Ray crystallography and for the first images of DNA, the diffraction pattern looked like the picture to the left.
- Most scientists do not look at DNA to the atomic level like in X-Ray crystallography, but rather want to see it inside of a cell. The DNA in a cell is inside the nucleus and certain dyes (such as the Hoechst dye) bind to DNA. Under UV light, the Hoechst dye glows, showing exactly where the DNA is in the cell. If you look at the picture to the right, you can see the outline of three cells and the blue DNA inside the nucleus of those three cells. Why would a scientist want to see where the DNA is and what it looks like? You can learn a lot from just looking at the DNA. For example, whether or not a cell is dividing or dying, which can be really important if you want to know whether or not the cancer cells you are studying die when you treat them with a drug.
- Scientists don’t always look at the DNA directly inside of a cell either. For an experiment they may want to isolate the DNA (meaning, take the DNA out of a lot of cells to study it) and then manipulate it in some way (sequence it, amplify it, modify it, etc). Once my mom asked me how big DNA is when you take it out of cells and work with it in the lab. Well, the answer is that you need a LOT of it to even see it. In the lab, we may grow bacteria in 5 ml of growth media, which after growing overnight contains 10,000,000,000 cells. We then bust these cells open with a detergent (like soap, but not soap), spin out all of the extra bits of cells, and then force the DNA to show itself by adding an alcohol like ethanol in a process called precipitation (if you want to learn more about the details, check out this article). How much DNA do you get in the end – well it depends, but it’s not a lot, visually at least. And what does it look like? See the whitish smear at the bottom of that tiny tube? That’s the DNA.
Are there other ways to see DNA? YES! But many of them are based on dyes like the one described in #2 above. At some point, we’ll definitely talk about them in the context of analyzing DNA sequence and running gels. And I’m not talking at all here about “seeing” DNA by determining it’s sequence, even though that’s important too.
So now that you know a few ways that scientists see DNA, it’s your turn. Grab a lab partner, and isolate DNA on your own!! Don’t know how? No problem! There are a number of different ways to isolate DNA at home, the most common being from the cells of an onion or the cells of strawberries. The experiments for extracting DNA from ONIONS or STRAWBERRIES are linked. At the end of the experiment, what will you see? Long strands of isolated DNA from all of the onion or strawberry cells. Enjoy and please share photos and stories of your DNA isolation adventures!