Extracting DNA

Time: 45-60 minutes

Materials (per classroom)

Blender / 3 Bananas / Container with ice (for test tubes)

Materials per group

2 small plastic cups / Plastic spoon / 20mL distilled water / 1 paper clip
5 mL detergent (clear-colored Suave shampoo) / 1 magnifying glass / Pinch of table salt / 1 eyedropper
Sealed test tube containing 14 mL of ethanol / 1 coffee filter

Getting Started

  1. Discuss DNA in living organisms. DNA is the single most important molecule in living cells and contains all information that determines who you are and what you look like. Everyone’s DNA, other than identical twins, is different. Have you ever seen DNA used to solve crimes?
  2. DNA in the nucleus is grouped into 23 sets of chromosomes that are called your “genome.” What do we share 99% of our DNA with? How about 50%?
  3. There is no right or wrong answer, but for today’s purpose the answer is 99% with chimpanzees and 50% with bananas!
  4. Discuss extracting DNA and how it’s related to biotechnology. How is the separation of the unwanted substances in a cell? How do you make sure the DNA is not broken

Directions

  1. In a blender, mix a ratio of one banana per one cup (250ml) of distilled water. Blend for 15-20 seconds, until the solution is a mixture. (You will need about 2 bananas/class).
  2. Make groups of 3-4 students. Have the students send one group member to the front to collect: 1 eye dropper, 2 small plastic cups, 1 spoon and a coffee filter.
  3. Go around the room and pour 1 teaspoon of shampoo, 20 ml of distilled water and 2 pinches of salt into a cup for each group. Ask the groups to stir the solution.
  4. Once their solution is well-combined, go around the room and add 3 heaping teaspoons of the banana mixture.

Note: Feel free to ask the teacher help distribute these items to save time.

  1. Have the groups stir their banana-shampoo-salt solution for 5 minutes. As they stir, discuss what is going on in their cups.
  2. While one member continues to stir the solution, have the groups prepare their second cup by folding the coffee filter’s edge around the cup so that the bottom of the filter is one inch from the bottom of the cup. Make sure that the filters are not touching the bottom of the cup.
  3. Filter the mixture by pouring it into the filter and letting the solution drain for several minutes until there is approximately 5 ml of filtrate to test.
  4. Pass out the test tubes of cold rubbing alcohol.

Note: Rubbing alcohol works best when cold. Try to keep it in the fridge overnight, and in ice or in a fridge during most of the setup of the activity

  1. Have the students fill their eye droppers with the filtered solution and add it to the test tube.
  2. Let the solution sit for a few minutes without disturbing it. Ask one student from each group to hold the test tube upright-stress the importance of not shaking/bumping the tube. White, stringy DNA will begin to appear where the water and alcohol meet. You will usually see DNA precipitating from the solution at the water-alcohol interface as soon as you pour in the alcohol. If you let the preparation sit for 15 minutes or so, the DNA will float to the top of the alcohol.While waiting go into the discussion portion.
  3. Use the end of a paperclip to collect the DNA. If the students want to keep their DNA, they can let it dry on a paper towel. The students can “examine” their DNA with the magnifying glasses.

Discussion

  1. Discuss what the shampoo may be used for.

The detergent breaks down the cell membrane by dissolving the lipids and proteins of the cell and disrupting the bonds that hold the cell membrane together, leaving the DNA.The shampoo works just like it does in our hair-it bonds to the proteins in the cell wall and causes them to precipitate out of the solution.

  1. Discuss what the salt may be used for.

Although the shampoo freed the DNA, it is still tightly wound around different proteins. The salt is an enzyme that works like a pair of scissors to cut out the DNA.

  1. Discuss the impacts of Genetic Engineering.

Genetic engineering involves the isolation, manipulation and reintroduction of DNA into cells or model organisms, usually to express a protein. The aim is to introduce new characteristics or attributes, such as making a crop resistant to a herbicide, introducing a novel trait, or producing a new protein or enzyme, along with altering the organism to produce more of certain traits. Examples include the production of human insulin through the use of modified bacteria, insect protected cotton, and herbicide tolerant soybeans. The first commercially grown genetically modified food crop was a tomato created by California company Calgene called the FlavrSavr. This tomato was made more resistant to rotting. Future envisaged applications of GMOs are diverse and include drugs in food, bananas that produce human vaccines against infectious diseases such as Hepatitis B, metabolically engineered fish that mature more quickly, fruit and nut trees that yield years earlier, and plants that produce new plastics with unique properties.