Observations and results
The stringy substance that you see is DNA! It has been removed from the millions and millions of cells that make up the banana. All living things have DNA. The more similar and closely related two living things are, the more similar their DNA is. Every human shares 99 percent of his or her DNA with every other person. Furthermore, human DNA is very similar to that of other species. We share most of our genes, which make up DNA, with fellow primates such as chimpanzees and with other mammals such as mice. We even have genes in common with the banana plant!
In this activity each material plays a specific role in helping to extract the DNA from the cells. For instance, the detergent or soap helps to break down the cell's outer membrane, and the salt helps to separate the DNA from other materials in the cell. And because the DNA doesn't dissolve in alcohol, this substance helps the DNA clump together in a separate layer.
Share your banana DNA observations and results! Leave a comment below or share your photos and feedback on Scientific American's Facebook page.
Cleanup
You can wash the bag and reuse it. Pour the banana liquid and alcohol down the drain and wash out the cup.
More to explore
"Can Science Save the Banana?" from Scientific American
"Bar Code of Life: DNA tags help classify animals" from Scientific American
DNA model activity from CSIRO's Double Helix Science Club
DNA Interactive site from Cold Spring Harbor Laboratory
My First Book about DNA by Katie Woodard, ages 9–12
Have a Nice DNA by Frances R. Balkwill, ages 9–12
Up next…
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What you'll need
• Tweezers
• Cotton swab
• Binder clip
• Several different kinds of seeds, grains or nuts that differ in size and shape. It is best if you have a wide range: some that are tiny (for instance, grass seeds or couscous), some that are medium-sized (black-eyed peas or lentils), and some that are larger (almonds, cashews, walnuts or hazelnuts).
• Timer with a second hand or clock
• Dish
• Paper
• Pen or pencil
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13 Comments
Add CommentThis is very simple but of great importance experiment you have given. Also materials required are so common.
Reply | Report Abuse | Link to thisI believe this is a best experiments for students to see DNA.
The analogy of DNA being a blueprint for a living organism is not very good. While a blueprint can be followed to build a structure; carefull observation of the structure can be used to create a blueprint. No amount of observation and measurement of a banana will allow us to recreate the banana DNA. Richard Dawkins has suggested the analogy to origami is a much stronger than the blueprint analogy. I agree with his assesment but I wonder if even better analogies can be created. Any ideas?
Reply | Report Abuse | Link to thisCool experiment but I'm curious about what each step in the process accomplishes. What is happening when the salt water is added? What then happens when the soap is added? And then the alcohol?
Reply | Report Abuse | Link to thisOnce the DNA is separated, are there more experiments possible that show properties of the DNA? Like decomposing it into sugar, organic bases and phosphoric acid and performing identification experiments on those?
Reply | Report Abuse | Link to thisI actually don't think it's such a bad analogy. If one studies the proteins and RNAs within a cell it is simple to infer a large amount of information about that cell's DNA. The obvious difference is that the blueprint of a cell would have to contain more information than that encoded by DNA. But this is the problem of explaining complex concepts to the public--too much information engenders disinterest, while too little may be misleading. Honestly, if you had to explain the engineering principles that go into developing a blueprint I suspect you would lose most people.
Reply | Report Abuse | Link to thisAbout that blueprint again. If you have a finished building it's relatively easy to reconstruct a blueprint from that. Not so for reconstructing the DNA sequence from an finished living being. You can better compare the workings of DNA with a cooking recipe. With the recipe it's easy to make a cake, but try to reconstruct the recipe once the cake is finished...
Reply | Report Abuse | Link to thisThe salt-soap mixture "lyses", or breaks apart, the individual cell membranes in the banana, thus releasing the DNA molecules into the solution. The alcohol works to condense and precipitate the DNA into the compact form you get at the end.
Reply | Report Abuse | Link to thisSo, you could equally say I'm seeing atoms of carbon, hydrogen, oxygen etc., but what I'm really seeing is slimy mucus. How can I prove it's more than the equivalent of phlegm?
Reply | Report Abuse | Link to this"How can I prove it's more than the chemical equivalent of phlegm?"
Reply | Report Abuse | Link to thisBy agarose gel electrophoresis followed by staining with the fluorescent dye, ethidium bromide:
http://www.vivo.colostate.edu/hbooks/genetics/biotech/gels/agardna.html
Excellent article and comments...Thanks!
Reply | Report Abuse | Link to thisWe've linked to this over at Genome Engineering http://www.genome-engineering.com/extracting-dna-at-home.html
Reply | Report Abuse | Link to thisJust curious but wouldn't it be better to remove the banana/aqueous layer before gathering the DNA? It could be removed a turkey baster or syringe I think. Neat idea. Onions are good to but have the acid-problem. Thanks.
Reply | Report Abuse | Link to thisUm...How do i get the deoxyribonucleic acid out. I tried but it always slip> D:
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