While working in the lab last week, one of my tasks was to isolate DNA and RNA using TRIzol. It was a long protocol involving lots of pipetting, mixing, and centrifugation. And of course, lots of waiting in between steps.
But the protocol isn’t what I want to talk about in this post. It’s the preparation I did in advance of starting the RNA and DNA isolation. To do this isolation, you need to make a number of solutions and dilutions. So as we were prepping for the procedure, my lab supervisor handed me several bottles of concentrated solutions and a powder and basically told me to go at it.
Hm. Right. For about 5 seconds, I stared blankly at my composition notebook and calculator. Then I realized that this was exactly what we had learned to do in General Chemistry last year. We had never actually made the solutions – merely done the word problems from the book – but the concepts were the same.
So I took the bottle of sodium citrate that I was supposed to use to make a 0.1 molar solution in 10% ethanol, wrote down the molar mass off the bottle, and calculated how many grams I would need to make 10 mL of the solution (remembering that molarity is moles per liter). Then I took the 100% ethanol bottle and diluted it 1:10 (making 10 mL) in a 15 mL plastic tube. After that, it was simply a matter of mixing the powder in the 10% ethanol. Easy, right? Yep, easy – if you paid attention in Gen Chem – which I did.
By the time I finished with the sodium citrate solution, my confidence had shot up. So diluting the 1 molar sodium hydroxide to 8 millimolar was a cinch.
But the proof is in the pudding, right? So after I finished isolating the DNA, I went to the NanoDrop – this awesome machine that measures the concentration of nucleic acids based on a teeny tiny drop (1 – 1.5 microliters) of the solution – and checked the concentration. More than 900 nanograms per microliter! That sounds like nothing, but for a DNA concentration, it’s quite a lot. And it’s more than enough to run the future reactions we want to do.
When I actually use something I learned in class, it reminds me that yes – these classes truly serve a purpose. And that is a good feeling.