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Public Health Summer Immersion Program 2017

Public Health Summer Immersion: Extracting DNA – One Banana at a Time

  • It’s day three of Public Health Summer Immersion at Massachusetts College of Pharmacy and Health Sciences (MCPHS), and high school students are listening intently to Crystal Ellis, PhD in White Hall on the Boston campus. She’s holding a beaker in one hand – and a banana in the other.

    She’s guiding the students through a lecture called “Do your ears hang low? The role of mutation in the evolution of human traits,” and has just reached the hands-on lab activity. She’s going to demonstrate how to isolate DNA from a banana.

    “DNA has a negative charge to it, so it dissolves very easily in water,” explains Dr. Ellis. “That’s a bummer, because we want to be able to see that DNA. How do we get it out of the water? How do we make it fall out of solution?”

    The students divide themselves into groups of three or four, their tables filled with the equipment they will need for the lab. Soon, students are mashing up bananas, then adding a detergent and salt solution. This step becomes very important later, explains Dr. Ellis. She then guides the students through straining the mixture through a cheese cloth.

    Caroline, a rising junior at Winsor School in Boston, is carefully adding meat tenderizer to her team’s banana liquid. Dr. Ellis explains that the tenderizer works as an enzyme to break down the proteins in the banana. This is important, she explains, because the DNA in the nucleus is molded, folded, and protected by proteins that need to be cut away. "The meat tenderizer will also deactivate any other proteins in the cell that are capable of degrading DNA as part of the normal recycling action of any cell," explains Dr. Ellis.

    Next, current MCPHS students appear with buckets of ice cold ethanol. They carefully pipette ethanol into each team’s test tube.

    “We’re adding ethanol, in a very high concentration,” explains Dr. Ellis. “And this is where the salt we added earlier comes in. We’re looking to neutralize the charge. When we add salt to this mixture, that salt will also dissolve in water, become positively charged sodium ions, and those positive charges will become attracted to the negative charges on the DNA, and will start to neutralize that charge, making the DNA a little more difficult to dissolve in water.”

    Students around the room lean in to get a closer look at their test tubes, hoping to see DNA.

    “The ethanol we added at the end stabilizes the interaction, and when you stabilize the interaction between those two charges – boom – it falls out solution, turns into this white stringy precipitate and you can actually see it with the naked eye,” explains Dr. Ellis.

    And sure enough, it works. Students around the room discover the stringy precipitate in their test tubes. They’ve just extracted DNA – one banana at a time.

    Massachusetts College of Pharmacy and Health Sciences (MCPHS) offers immersion programs designed to give high school students hands-on experiences in the health sciences. Interested in future immersion programs? Email us at