DIY Science: How to Extract DNA from a Strawberry – University of Leicester


Pretty much everybody has heard about DNA from the telly and it’s really popular for people to get their DNA tested to tell them about things like their ancestry. But hardly anyone is actually seen what DNA actually looks like, so this is a really quick little experiment that you can do at home, using household goods, so you can actually see DNA yourself. So what we’re going to do is we’re going to get DNA from strawberries and what you need to do is just take the tops off of the strawberries because it’s really hard to break up those leaves and things like that. So what we’re going to do is we’re going to put the strawberries into a bag, because the DNA that we are interested in is in the cells and it’s in a little structure known as the nucleus. So what we need to do is we need to break open the cell walls and get to that DNA, by squishing up the strawberries. So this is going to take a little bit of time and what you want to do is you want to get them as nice and as smooth a paste as possible, so you just have to work at it basically. Okay, now that we’ve broken down the cell walls a little bit just mechanically what we want to do is we want to add a little bit of water, because we’re going to get the DNA to come into solution. So we’ve got about a 100ml of water here, not terribly much and then we can break down the cell walls not just mechanically by squishing them but also using washing up liquid because the cell walls are made up of a fatty material and so the washing up liquid, just a few drops is fine, is going to help to break down those cell walls and break down the nucleus for us as well, to release that DNA into solution and then we’re just going to add a pinch of table salt and what that will do is help to clump the DNA strands together. So let’s close this back up again and we’re going to give it a little squish. So what’s happening now is you’ve got the DNA, it’s coming out into the water, but there’s lots of things in here that we don’t want, so bits of cell wall, bits of cell that we don’t want, we want the DNA that’s come into solution. So what we need to do is we need to filter out those bits we don’t want and we’re just going to do that with filter paper, this is a coffee filter, just pop it into a little funnel there and then just pour this in and then what happens is the cell walls, the bits of stuff we’re not interested in hopefully will stay in the filter paper and the stuff we are interested in, the DNA will come through in that water. So that’s going to take a little while for that to happen so you just have to let it go for a bit. Now what’s happened is the DNA has come through and it’s in that water, now DNA stays quite nicely dissolved in water but it doesn’t stay dissolved in alcohol, so what we need to do is we need to add alcohol. So what we’re going to do is we’re going to pour this into here, now you can do all this with your own spit if you like but it takes quite a bit of time to get enough spit together to be able to get a really good set that you can look at. Now I have got a really high proof alcohol, this is actually a white rum really high proof, which is great but you can use methylated spirits if you want to use a cheaper option and what we’re going to do is we’re just going to add alcohol to the top of this. Now you don’t want to mix it in too much, what you’re going to do is you’re going to basically rest this alcohol here, on the top and you’ll see that where the two layers meet the DNA is going to start to come out of solution, it doesn’t like being in solution in the alcohol it can’t do it. So what it does is it starts to precipitate out, we’ll do about equal amounts of each one, so equal amounts of alcohol to strawberry juice, like this and you can see it already. So you can see what looks like, sort of like clouds or cotton wool and that’s the DNA starting to precipitate out of solution. So if you have a look where the two layers meet you can see what looks like cotton wool, little strands of cotton wool coming out of solution there and that’s the DNA starting to precipitate out. If you leave it for a little bit what you’ll get is a layer of what looks like clouds and that’s the DNA that you can actually see there. So we’ll just leave that for a bit and you’ll get a better look at it like that and that’s something you can really easily do at home so you can actually see DNA yourself.

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