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Kiwi DNA

Introduction
Public summary: 

In this experiment we get DNA out of living cells in kiwi fruit. The DNA can be made fully visible to the human eye - no microscopes or magnifying glass needed! Done in less than 5 minutes in front of your eyes.

Breaking open cells of a kiwi fruit and making the DNA inside visible to the human eye
Useful information
Kit List: 

Consumables: Kiwi fruit, salt, washing up liquid, 96% ethanol or 99% isopropanol (*caution*)
Equipment: Slow cooker, plastic pint glasses, half rolling pin (for mashing), sieve, plastic champagne flutes, ice bucket, bowl (for liquid waste), cloths (it's generally messy), sharp knife (*caution*), chopping board, spoon/fork/cocktail stick/pipette, model of DNA, posters about DNA and proteins
*NB. Ethanol/isopropanol need to be kept out of reach of children, as does the sharp knife. If possible, keep the knife and any spare alcohol in the box when demonstrating*

Packing Away: 

*Do not leave kiwi fruit in the water bath... they might end up there for months if we don't use the experiment again soon and green slime is not very nice!*

Frequency of use: 
5
Explanation
Explanation: 

Kiwi DNA repack for the 2011 Summer Roadshow

• Slow cooker, run on high for 30 mins in setup, then turn down to "warm" heat before visitors arrive.
• Stores box (small blue) has spares of most of the kit in the kiwi DNA box.
• Please use only 1-2 cm3 of ethanol/isopropanol per experiment to conserve our supplies for the whole roadshow. There are some plastic pipettes to help you with this.
• Poking the DNA at the end. As well as the cocktail sticks described in the main explanation we’ve now got some clear plastic cocktail stirrers, which are easier to get into the cocktail glasses when you’re getting the DNA out.
• RNA model: in a plastic Tupperware tub in the main box, and new for 2010. Don’t feel you have to use this, but if you want to talk about DNA being used as a template to make proteins it’s a nice prop, and has the same colour coding.
• Laminated sheets: provide some useful images, and there’s a wheel to show how DNA code is used to encode amino acids. Please try to dry these if they get damp during the day.
• DNA model in box. Roughly 1.4bn times bigger than real life (if my maths + memory is correct).

Overview

Breaking open the cells of a kiwi fruit to extract the DNA. You can demonstrate it to one family or a whole crowd as a show, discussing cells, DNA and proteins!

Tips for demonstrating:

  • It's difficult for the audience to participate in the practical activities, so it's more of an interactive show with lots of questions and answers.
  • Do the preparation work before the audience arrives! I work the experiment as a continuous process and maybe use five kiwis in the day.
  • Be aware that young children won't know a lot of science. For instance, don't assume they know about cells (most don't), they know about humans being animals and that plants and animals have a lot in common. They might not even have reached the stage where they relate the idea of parts of the body having different structures and functions.

Preparation

You need to have:

  • Isopropanol or ethanol on ice (as it works best when cold). If no ice is available, isopropanol seems to work better at room temperature than ethanol.
  • Water bath heated to "warm"
  • Use masking tape or similar to divide the water bath into pint-glass sized sections so that the glasses don't fall over when you put them in the water bath
  • A kiwi or two peeled and cut into 1 cm chunks
  • A bottle of lysis buffer - contains washing up liquid, salt and water. As a general guide, in a bottle, put about 1/8 volume salt and dissolve in 3/4 bottle of warm water, then top up with washing up liquid and invert a few times to mix. You don't want it particularly thick, so err on the side of less washing up liquid - you can always add more.

Basic procedure and explanation

The steps of the experiment are below in bold, with an example way of talking through the experiment for younger children. It includes questions and answers (of course if you get the right answer modify your reply). Try and use simple words and up the language as you deal with older kids or adults. You can use this experiment as a basis for talking about scale, with respect to cells and molecules and also as a basis for discussing what DNA does, and how similar our DNA is to kiwis (>50%).

You may want to have some mashed DNA in lysis buffer incubating, and use that rather than the one the group with you has prepared as it takes a while for the cells to lyse. Preparing a couple before you begin demonstrating also means you can check the lysis buffer is ok.

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Do you know what this is? It's a kiwi fruit. And what's a kiwi fruit made out of? (you'll probably get seeds, flesh, skin types suggestions)

What are all living things made out of? If I scratch my nail across this what do I have under my finger nail? Cells. Just as a house is made out of bricks every living thing is made out of cells but they're very small. There are different cells in the flesh to what there are in the seeds or in the skin and in you their are hundreds of types of cell. Different types of cells in your eyes, blood, brain and skin too.

First what I want you to do for me is mash up some kiwi fruit.

Add a lump of Kiwi to a plastic cup and get them to mash it with the rolling pin (gently!). You can explain that what they're doing is like demolishing a house, all you've got left is a pile of bricks.

Now what I'm going to add is some washing up liquid.

Add lysis buffer to the cup containing the kiwi to a depth of about 1cm and put the cup in the water bath. You can ask: what does washing up liquid do? (You'll probably get "it makes bubbles" at this stage!) What do you use it for? Cleaning plates. Well what does it take off the plates? The grease and fat. It does this by dissolving the fat: this is like what happens when sugar or salt disappears into water. A cell is basically a bag full of water and other important things like DNA, and the bag is made from fat so the washing up liquid dissolves and breaks up the material the bag is made from (the cell membrane). This releases everything that is inside.

What do you know about DNA? Discuss! DNA is like the plans for building us. Just like you need plans for building a hospital. But if you build a hospital it's useless unless you know how to build the doctors, nurses and beds inside them and the doctors and nurses know what to do. So it's not just the plans for building you it's also the instructions for how you should be run. Alternatively, DNA could be like an instruction manual for how to build a person (or kiwi), and there is some inside almost every cell in our body and every cell in the kiwi. What we're going to do is we're going to take the DNA from the kiwi fruit.

Take the kiwi mush/lysis buffer mix out of the water bath. So this liquid here is full of DNA.

Pour the liquid from the cup into a plastic flute through a sieve to remove the lumps. We need to separate the DNA from everything else in the mixture.

Get out the alcohol and pass it around the noses present, taking care to keep control of it. What does that smell like? (kids often recognise it as hand gel) It's not water, it's pure alcohol. I emphasize this as children commonly think anything that is liquid has water in it.

Using a pipette, put about two pipettes-full of isopropanol into the glass by pouring it down the sides of the glass so it doesn't mix too much with the rest of the mixture and forms a layer on the top.

Show the glass around. What you can see here are two layers, the green layer is the water with the DNA in and the clear layer is the alcohol layer.

Now do alcohol and water mix? Sure they do. Because if you look at a bottle of whiskey or beer there's only one layer there. So what's happening is the water is moving up into the alcohol layer and the alcohol is moving down into the water layer *wibble your fingers about* and the two are mixing.

The DNA is the stringy white stuff that collects between the two layers. Can you see anything appearing between the two layers? Some stringy white stuff forming? That's the DNA. It takes a while to see this sometimes, so you can either show them a previous group's glass or pick up some of the bottom layer with a pipette and slowly release it through the top layer. It's helpful to have a few really good examples lying around to show "one that we made earlier", to make sure that they see the DNA even if the experiment didn't work for them.

Possible discussion points:

Now what I'm going to do is try and pick up a single molecule of DNA. (showman mode, on the end of a spoon I fish a little bit out.)
What's the largest number you can think of? Because what i have here on the end of this spoon is billions molecules of DNA. Just as the Kiwi is made up of the bricks we call cells the cells are made up of molecules.

So how big do you think one of these molecules is? It's about a millionth of a millimetre across. But because DNA is an especially long molecule it's a metre long. Now what I want you to do is use your imagination and I'm going to pick up one molecule of DNA *pretend to pick up a very thin strand and pass it to a child to hold and stretch it out to about a metre*

Now this is a molecule of kiwi DNA and if we use your imagination again I can pick up a molecule of your DNA and that's about a metre long too. Now in your right hand we've got a molecule of kiwi DNA, this is the instructions on how to build and run a kiwi and in your left hand we have your DNA which is the instructions on how to build and run you. Now how similar do you think these two are.

How much is the same? (Sweepstake the entire audience) About 85cm is the same (alternatively 85% the same), that's this much. (Mark out 85 cm and you've got around percentages!)

That's because both you and the kiwi are made up of cells and the cells in the kiwi do the same sort of thing as the cells inside of you. They make more cells, they use sugar and oxygen to make energy and use protein and fat. So who do you think is the most similar person in the worl to you? It's your brother or sister, not your mum or your dad. Which is why you've got to look after you're little brother as they're the most similar person in the world to you. You're all but a tenth of milimeter the same as you're brother or sister and you're all but about millimetre the same as anyone else in this room. You're all but 2 cm different from a chimpanzee. Which is why I think we should look after everything in this world as we're really not very different from anything else.

Risk Assessment
Date risk assesment last checked: 
Sat, 12/01/2019
Risk assesment checked by: 
abb53
Date risk assesment double checked: 
Mon, 14/01/2019
Risk assesment double-checked by: 
Polly Hooton
Risk Assessment: 

Heat mixture of salt, water, washing up liquid and mashed up DNA (60°C) for 15 mins. Decant some of the liquid into a plastic champagne flute. Drizzle an equal volume of ice-cold ethanol/isopropanol on top. DNA visible at interface. Using model and posters to explain DNA.

Hazard Risk Likelihood Severity Overall Mitigation Likelihood Severity Overall
Ethanol/isopropanol Irritant, flammable, and very toxic if ingested 2 3 6 Only have a small amount of ethanol/isopropanol out, away from naked flames AND THE PUBLIC. Avoid contact with skin and eyes. Do not ingest. Only allow parents and children to mash kiwi on its own - not once mixed with detergent or ethanol/isopropanol. Ensure eyewash is nearby and that you know the location of it.
In case of contact, wash off skin. Use eyewash to wash out of eyes if trained and confident to do so, and call first aider. If ingested call first aider immediately.
1 3 3
Water bath Hot water can scald. 3 3 9 Maintain the water bath at 60°C out of reach of children. Ensure has passed PAT test in last 2 years. Ensure cables are taped to the ground/table to reduce risk of person tripping on/pulling the cables.
In case of burns, run cold water over affected area for at least 10 mins. Call first aider.
2 3 6
Glassware and plastic containers If broken can cause cuts. 2 3 6 Dispose safely of any broken glassware immediately. Keep spares out of reach. Check plastic container and ethanol/isopropanol are compatible.
First aider to be summoned in the event of an accident.
1 3 3
Kiwi/detergent solution Solution is harmful, especially should it be splashed into the eyes. 2 3 6 Do not allow children to mash the kiwi once it has been mixed with detergent or ethanol/isopropanol. Keep all mixtures within demonstrator's reach. Avoid contact with eyes or the mouth. Try to work on a surface which is not at eye level. Demonstrator can show children how to mash the kiwi without splashing kiwi everywhere. If any does splash out of the container, clean up immediately. Know the location of the nearest eyewash.
In case of contact with eyes, use eyewash to wash out of eyes if trained and confident to do so and call first aider. If ingested call first aider immediately.
1 3 3
Sharp knife Possible cuts/other injuries. 3 3 9 Supervised use only. Keep sharp knives away from children. It's impractical to cut all the kiwi beforehand, but after cutting fresh kiwi, keep the knife in the pencil case provided and keep this in a drawer/out of sight.
First aider to be summoned in the event of an accident.
1 3 3
Wet surfaces Slip hazard. 3 2 6 Wipe up any spills. Use wet floor sign if necessary. Keep experiments away from electrics.
First aider to be summoned in the event of an accident.
2 2 4
Kiwi fruit Small risk of allergic reaction to kiwi fruit in a small minority of people. 2 3 6 Demonstrator to check that visitors are not allergic to kiwi fruit before commencing the experiment.
In case of contact, call first aider. Rinse skin with clean water.
1 3 3
Heating element/stirrer Risk of heat element and stirrer overheating if not covered by water. 2 3 6 Demonstrator to ensure that element is always covered with water and stirrer is always rotating.
In case of accident, turn off electricity at mains. Call first aider if necessary. Allow to cool before using again.
1 2 2
Small parts Small pieces in model may present choking hazard. 2 4 8 Keep model completely assembled and prevent children taking it apart. Keep the black stopper on top of the stand as this prevents the rest being disassembled.
If child ingests small part of model, call first aider immediately.
1 3 3
This experiment contains mains electrical parts, see separate risk assessment.
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Images
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