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 *** 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, protein, the works!
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, 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. Go carefully!
*** PREPARATION ***
Start the process off by peeling a kiwi and cutting it into 1-2 cm chunks.
Mash it then add some lysis buffer (made with water, detergent and salt)
Incubate at 50 oC.
Test it out yourself after 15 minutes by pouring some of the supernatant liquid into the glass then some of the chilled alcohol on top. Always keep a good result handy incase it doesn't work.
*** BASIC PROCEDURE AND EXPLANATION ***
This is my routine, as i would do it for younger children. It includes questions and answers, of course if you get the right answer modify you're reply. Try and use simple words and up the language as you deal with older kids or talking to adults.
I use it as a basis for talking about scale, with respect to cells and molecules. And also as a basis for discussing how similar our DNA is to kiwis. About 85%. One of the difficulties is younger children understanding percentages and I have a way around that.
Hellos and all that. 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. I've got about 100 cells underneath my fingernail.
Their 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. Now what I want you to do for me is mash up some kiwi fruit.
Add a few lumps of Kiwi to a cup of Kiwi mush and get them to mash it.
Now what you'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 enough that there's a thin liquid layer on top of the lumps and put in water bath
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. Do you do the washing up? *Teasing to amuse the parents!*
Well next time you're doing the washing up put some water in the frying pan then add some washing up liquid. The lumps of fat floating in the liquid break up into smaller lumps and then smaller lumps and then such small lumps that they disappear into the water. Do you know what that's called?
Do you know what it's called when sugar or salt disappears into water? Being dissolved. So washing up liquid breaks up / dissolves fat.
Do you know what's in a cell? A cell is like a bag full of water but the bag is made out of fat. Inside there's lots of important stuff floating around and the DNA. What do you suppose happens to the cell when you add the washing up liquid?
It breaks up the cell walls.and everything that's inside the cell gets spilled out. So the DNA inside the cell gets spilled out. 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 who 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. And what we're going to do is we're going to take the DNA from the kiwi fruit.
So this liquid here is full of DNA.
Pour out some of the water from the top into a glass or get an assistant to do it.
So what we're going to do is get out that DNA but first I want you to tell me what this is.
Get out the alcohol and pass it around the noses present. What does that smell like? It's not water, it's pure alcohol. I emphasize this as children commonly think anything that is liquid has water in it.
For about 9+ children, as some motor skill is required, I address them with Have you ever poured champagne? The things about pouring champagne like pouring coke is that if you pour it down to the bottom of the glass it fills with bubbles. If you don't want to get any bubbles in it you need to pour it down the side of the glass, now that's what I want you to do with the alcohol. If you pour it gently into the glass because the alcohol is lighter than water it will float on the water.
(We use a champagne glass so this works quite well.) Get them to pour out about a centimeter or so. 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 *wibbly finger demo!* and the two are mixing.
Can you see anything appearing between the two layers? Some stringy white stuff forming? That's the DNA.
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 a billion billion 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.
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Risk AssesmentsKiwi DNA Extraction Risk Assessment Electric Parts Risk Assessment
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| Authored by: Dave on 28/04/04 @ 22:44 BST |
I found this data at:
http://www.koshland-science-museum.org/exhibitdna/intro03.jsp
Another human? 100% - All humans have the same genes, but some of these genes contain sequence differences that make each person unique.
A chimpanzee? 98% - Chimpanzees are the closest living species to humans.
A mouse? 92% - All mammals are quite similar genetically.
A fruit fly? 44% - Studies of fruit flies have shown how shared genes govern the growth and structure of both insects and mammals.
Yeast? 26% - Yeasts are single-celled organisms, but they have many housekeeping genes that are the same as the genes in humans, such as those that enable energy to be derived from the breakdown of sugars.
A weed (thale cress)? 18% - Plants have many metabolic differences from humans. For example, they use sunlight to convert carbon dioxide gas to sugars. But they also have similarities in their housekeeping genes.[ Reply to This ]
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| Authored by: selina on 30/07/04 @ 21:42 BST |
Q: How do you know the white stuff is DNA?
A: Erm... (anyone got any ideas?)
Q: Why does the DNA precipitate out when you add cold ethanol?
A1: DNA is soluble in warm water but insoluble in cold ethanol.
A2: DNA has hydrophobic and hydrophilic regions, so it lines up with hydrophobic bits in the alcohol and hydrophilic parts in water.
Thinking about this again i'm not sure the hydrophobic/philic argument works as all the h-phobic parts of DNA should be buried on the inside of the double helix with h-philic parts on outside. Unless DNA is completely denatured i.e. H bonds between bases broken there shouldn't be any h-phobic parts available.[ Reply to This ]
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| Authored by: Anonymous on 31/07/04 @ 11:24 BST |
Q1 - How about an argument about acquired knowledge to answer this one? It must be a polymer however as it is stringy.
Q2 - DNA is also soluble in cold water. it becomes insoluble in water / alcohol mixtures. I share your scepticism about A2. It might have something to do with the shielding of the phosphate charges. As the shilding of the charges due to solvent becomes less adding alcohol, sodium ions are more likely to condense onto the phosphates... Perhaps as the charges become less shielded they interact with each other more and the polymer becomes less flexible... Solubility is a difficult question to answer.
Anthony[ Reply to This ]
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| Authored by: selina on 30/07/04 @ 21:44 BST |
| A good way to indicate percentages is to stick a metre long bit of masking tape onto the front of the table and mark off a metre. [ Reply to This ]
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