Banana DNA

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Biology: DNA, DNA Extraction
Grade Range: Elementary School, Middle School, High School
Format: Hands-on

This space is intended to describe the demonstration that is here. Please use this space to describe in short the demonstration, making sure to mention here if it will require any additional safety equipment or how easily it can be adjusted for varied grade levels. Use this page as a base layout for editing the wiki. Feel free to copy the layout onto other pages, and to put the content as needed into the page.

Contents

Materials

  • Banana or Other Fruit
  • Gauze
  • Centrifuge Tubes with Lids (two per group)
  • Cup or Bowl with Fork
  • Skewers (one per group)
  • Ethanol with an Ice Bath
  • Extraction Solution:
    • Liquid Soap
    • Salt
    • Sodium Citrate
    • EDTA


Safety Precautions

Please read the Dry Chemical section of the Demonstration Safety page before performing this demonstration.

Inform students that they should wash their hands after performing this demonstration.

Demonstration

Preparation: prepare the extraction solution. For every 500mL of liquid soap, add:

  • 146g Salt
  • 73g Sodium Citrate
  • 5g EDTA

This demonstration requires about 15mL of the extraction solution for each run, so adjust accordingly for the number of times you expect to present this demonstration. If you'd like, you can pre-mash the fruit for the demonstration, but it is better to mash it as needed.

  1. Give each group of 2-4 students two of the centrifuge tubes, a skewer, and a small wad of gauze. Inform them that they will be extracting DNA from the fruit you brought in.
  2. Mash up the fruit, and give each student a small scoop (about 10mL) in one of their centrifuge tubes. Have them add 15mL of the extraction solution, then put the cap on and shake the tube for 1-2 minutes.
  3. Have the students now put the gauze over the second centrifuge tube, and slowly pour the solution through the gauze to remove any big chunks.
  4. Add between 10 and 20mL of the chilled ethanol into their strained solution, and have them gently swirl it. They will see long strands start to precipitate out! Have them use their skewer to collect the strands and lift them out of the solution. Those strands are the DNA from the fruit!


Why This Works

DNA stands for DeoxyriboNucleic Acid. DNA is your body's instruction manual for living - it's a molecule that stores information on everything about your body. DNA is made up of four different building blocks called base components. These components are Adenine (A), Cytosine (C), Guanine (G), and Thymine (T). A and T can bond, and C and G can bond, which creates two kinds of Base Pairs. These base pairs can then bond with other molecules, like sugar molecules and phosphate molecules, to make a Nucleotide. Nucleotides string together to form Genes, which link together to create our Chromosomes. All the chromosomes in your body are collected into a single Genome that is made up of about three billion base components, and that genome is our DNA!

Almost all of your cells contain two copies of your full genome. This is because your DNA is coiled up in your cells, and it twists into a shape called a double-helix. If you unwound it all, it could stretch almost six feet! The double-helix shape of the DNA makes it easy to duplicate. Since A and T can only bond with each other, and C and G can only bond with each other, your DNA can split down the middle, and then each side can replicate the other. A way to think of it is if you were making a peanut butter and jelly sandwich. If your sandwich has only peanut butter, then you know that it needs the jelly. Likewise, if only has the jelly, then you know it needs the peanut butter! When a cell dies, a nearby cell will split its DNA and separate into two cells. Then each cell can recreate the other half of their DNA by seeing what is missing!

Almost every type of living creature on Earth uses DNA, just like humans. It's the information stored in the DNA that causes differences between organisms and species. You get your DNA from your parents - whatever information their DNA held is passed onto you. This is called genetic inheritance. About 99% of your DNA is the same as mine, and every human being; we all have almost exactly the same DNA. It's the small differences in your DNA that give people different eye colors, hair colors, skin colors, heights and other unique traits. Your DNA is what makes you so unique!

Additional Information

  • This demonstration pairs well with the Candy DNA.
  • Fun fact: We share about 98.8% of our DNA with Apes, signifying that we have a common ancestor. We also have shared DNA with mice (90%), cats (90%), dogs (84%), and even flies (50%). However, we do not share 50% of our DNA with bananas. Rather, we share only about 17% of our DNA with bananas, as a conservative estimate. This paper has more information on the banana genome.
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