Program 28: Banana DNA

For our final program of 2013, I wanted us to dig deep into science. That’s right – I broke out the test tubes and magnifying glasses and even some pipettes! This month we revisited one of my favorite programs from the past: Banana DNA. Our G3 scientists learned how to extract actual DNA from bananas!

dnaAs always, the program kicked off with a brief discussion. We talked about the nature of DNA itself. Do humans have anything in common with a rhinoceros? Or a frog? Or even a tree?  The answer to all questions was YES. All life forms contain DNA, which determines what that life will look like and more. In the case of our bananas, the DNA is what tells the banana to be a certain color, or a certain shape, or a certain flavor. We watched some great videos from Dole about what goes into harvesting and shipping all of their bananas. [Video 1: Dole Banana Development & Care; Video 2: Dole Harvesting Bananas.]  I also pointed out a sheet of fun banana facts that each scientist could take home with them.

Cavendish Banana...soon to be extinct?

Cavendish Banana…soon to be extinct?

One very interesting thing we discussed is the fact that most Americans eat only one type of banana: the Cavendish. And due to a fungus that is attacking Cavendish banana plants around the world, in 5 or 10 years the Cavendish banana could very well become extinct! When that happens, we will all be forced to begin eating a completely different kind of banana. Our G3 scientists’ children or grandchildren may never know what a Cavendish banana tastes like! Though this isn’t the first time a banana species has become extinct. Prior to 1950, most Americans would have been eating a banana called the “Gros Michel,” but a fungus made that banana species extinct before any of our young scientists (and maybe even their parents) were born!

OUR EXPERIMENT

Using the instructions from the magazine Scientific American as a guide, the G3 scientists discovered that we can extract the actual DNA from bananas using a few household items like dish soap, salt, rubbing alcohol…and of course bananas! I made a few tiny modifications based on experience that I’ll note below.

Our supplies for the day:

  • 1 ripe banana per scientist
  • 1/2 cup of distilled water
  • 1 resealable zip-top bag
  • 1 tsp. salt
  • 1/2 tsp. liquid dish washing soap (any kind)
  • Isopropyl alcohol (rubbing alcohol) (chilled in the freezer)
  • 1 coffee filter
  • 1 narrow and clear glass or test tube
  • 1 narrow wooden coffee stirrer

The first step was mashing up the bananas…something that we all enjoyed 🙂 Each scientist was given a whole banana sealed in a zip-top plastic bag. The goal was to achieve a “pudding” consistency. Both tracks did a great job of firmly, but gently, breaking apart all of their banana lumps and creating a bag of banana mush.

In a separate cup, we combined 1 tsp. salt and 1/2 cup of distilled water, stirring until the salt was dissolved. This salt water was then added to our banana “slurry,” gently kneading to combine the ingredients in the bag. We then added 1/2 tsp. of liquid dish soap to the “slurry,” again gently kneading to combine the ingredients.  This led us to our trickiest step:  straining our banana slurry (to collect just the banana liquid in a cup). [The soap actually helps to dissolve the membranes of the cell walls that hold the DNA, and the salt helps to draw the DNA strands toward each other.]

Photo Dec 05, 4 46 48 PMI made some modifications to our previous work with banana DNA (and to the steps as identified by sites like Scientific American) to help with our success. Each scientist placed a coffee filter in a clear plastic cup, holding it in place with a rubber band. [This was an important and successful improvement to the process! In the past, so many of our filters fell back into the cup forcing the slurry to be restrained time and again.] Once we had maybe 1/4-1/2 inch of banana liquid in the bottom of our cups, each scientist carefully worked with a partner to remove the filter and remaining slurry from the top of the cup so that all that remained was the strained liquid beneath. Using pipettes, the G3 scientists then filled their test tubes about 1/2 way up with the banana liquid. They then used a clean pipette to add chilled isopropyl alcohol to the top of the test tube. [NOTE:  You can keep the alcohol in the freezer…it will stay in liquid form!]

The online experiment descriptions say you may have to wait up to 8 minutes to see some results, but almost all of our G3 scientists had immediate and successful results in hand. All G3 scientists were able to extract the white, fibrous, web-like DNA from their bananas! We tried out best to preserve the DNA bits in plastic baggies for those scientists that wanted a souvenir, but I think that photographs are the best way to preserve the results of this experiment. Check out the nifty slide show below of our scientists (from both tracks) in action:

In a final note, many of the banana facts I shared were obtained from the Chiquita banana web site.

I’m looking forward to seeing everyone in 2014 when our next programs will start. Happy holidays!

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