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Skip to 0 minutes and 9 secondsIn this next kitchen experiment, Lynne and I are going to be looking at how you can precipitate your DNA from saliva, showing that saliva is a lot more complex than just being a liquid. So how do we do that, Lynne? First of all we have to collect some saliva which we've actually done in this glass, here. If you want to do this at home, what we really want is some of the dead cells that are inside of your mouth mixed in with your saliva. So if you just sort of swish around in your mouth to just ease them off of just the side of your teeth. And then just spit into the glass. And just collect a little bit.

Skip to 0 minutes and 49 secondsThink of something nice to eat and the saliva flows very quickly. The next step we need, because we're in the kitchen really, is we just take some washing-up liquid. And what this washing-up liquid is going to do if we pour it in, just a little bit in here-- mix it in-- is just going to pop open the cells that are in the saliva. All the little cells that normally line the inside your mouth. They're going to pop open the cells and they're also going to pop open the nucleus that holds the DNA that makes you, you and me, me. OK? The next step is to take a little bit of salt, just ordinary table salt. I'll just put that in.

Skip to 1 minute and 37 secondsAnd what the salt is going to do is just going to make things sort of clump together a little bit and just help us to see the DNA when it comes out of solution. And then the final thing that's actually going to make the DNA come out of solution is vodka, alcohol. This can be any alcohol but I'm using vodka because it's a colourless liquid and you can see through it. But any sort of strong-ish alcohol will work because DNA will form a bit like a solid. It'll precipitate once it's in alcohol. We just pour some alcohol into here and we just wait and see-- just mix it around a little bit-- and wait to see what happens.

Skip to 2 minutes and 32 secondsThere it is! So the strands that you can see coming up through here are your DNA. And that's what makes you who you are, or me who I am. And mixed in with here, because my mouth is not as clean as I always like to think it is-- there are lots of bacteria in our mouth, they're the friendly bacteria. So there'll be some bacterial DNA mixed in with mine.

Skip to 3 minutes and 10 secondsA nice strand of DNA there. The real tips for making sure you can actually see your own DNA is to mix the washing-up liquid in with the saliva to start with, mix it in nicely. Don't put too much salt in. Just a pinch of salt is enough. And then if you just pour the vodka, or-- it really doesn't have to be vodka. Vodka's nice because you can see through it. But any strong alcohol, just pour it gently down the side of the glass and you'll get the layers forming then. And you'll immediately see the DNA starting to come out of the solution as little threads in the glass.

Skip to 3 minutes and 51 secondsAnd then, because it's a solid, it'll drop to the bottom, out of solution. So what can we do once we know that there is this DNA in the saliva that can be taken out. Is there anything you can do in the lab? There are lots of things we can do in the lab, and lots of lab researchers are getting quite excited now about the fact that you can take DNA out of saliva. Because the DNA can represent not just what's happening in your mouth-- so not only how you're unwell and have diseases of your mouth, but also diseases that come from other parts of the body. So we can take the DNA and we can look closely at it.

Skip to 4 minutes and 25 secondsAnd we can look at the difference between a normal sequence of DNA and maybe one that's been slightly changed by a disease process. And it's now being put forward as a marker of disease developing so it really is quite an exciting field. And so in the future, it may be that you actually don't go and have blood tests anymore. We just ask you to spit in a tube and we can use the saliva to see whether you're well or you're not well.

Kitchen experiments part 2: Extracting DNA from your saliva

We learnt about the basics of saliva in Week 2, but this experiment will demonstrate just how complex this liquid is by revealing the quantity of biological matter that saliva contains.

In this video, Dr Lynne Bingle shows you how you can extract the DNA from your own saliva at home, and explains why DNA samples from your mouth may be more popular in the future.

This experiment uses alcohol, so under 18s must ask permission and assistance from their parent/guardian before attempting the experiment.

Equipment needed:

  • A small glass or cup (something transparent is best)
  • Salt
  • About 5ml of Washing-up liquid (detergent)
  • About 10ml Alcohol* - we used cheap vodka but any strong, clear alcohol will work
  • About 5ml Saliva (although as much as you can get!)
  • A cocktail stick or toothpick - to spool the DNA strands onto

Note: If you do not want to use or buy drinking alcohol, you can also use Isopropyl alcohol (which is sold as a cleaning solvent).

Instructions

  1. First you will need to get your saliva. You’ll need as much as you can get, and thinking of food you like will help to stimulate the salivary glands. Remember to rub your tongue around your mouth as you do this in order to agitate and loosen cells from the epithelium (your cheek and gums) in your mouth.

  2. Add the washing-up liquid to the saliva (about the same amount as you have saliva). The detergent will break down the cell walls (a process called lysis) and expose the DNA (which is not affected).

  3. Now the cells are broken apart, we can add a small amount of salt which acts as a flocculant to make the cells’ contents stick together to make it easier to see. Give it a gentle swirl for 30 seconds or so.

  4. Finally we add the alcohol by gently pouring it down the side of the glass. This will allow us to see the DNA by bringing it out of solution. DNA is soluble in water, but not in alcohol. Adding the alcohol will force the DNA out of solution and make it visible. You might need to wait a few minutes for the solution to become clearer and to be able to see your strands of DNA.

  5. Use a cocktail stick or toothpick to ‘spool’ the DNA and see the strands more clearly.

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This video is from the free online course:

Discover Dentistry

The University of Sheffield

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