Unraveling the Code: Extracting DNA from Fruit!

A hands-on biology lesson where the student learns about DNA structure through introductory reading and then performs a simple lab experiment to extract and observe DNA from fruit using common household materials.

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Unraveling the Code: Extracting DNA from Fruit!

Materials Needed:

  • 1/2 Ripe Fruit (strawberry, banana, kiwi work well)
  • Small Ziploc bag
  • Measuring spoons (teaspoon, tablespoon)
  • Small clear glass or jar
  • Small sieve or coffee filter
  • Funnel (optional, helps with filtering)
  • Water
  • Table Salt
  • Liquid dish soap (like Dawn)
  • Ice-cold Isopropyl Alcohol (70% or higher, keep in freezer beforehand)
  • Wooden skewer or toothpick
  • Short reading material on DNA structure and function (prepare beforehand or use reliable online sources)

Lesson Procedure (50 Minutes):

1. Introduction & Reading (15 minutes):

  • Begin by asking: "What do you know about DNA? Where is it found? Why is it sometimes called the 'blueprint of life'?"
  • Provide the student with the prepared reading material about DNA. Focus on: What is DNA? What is its basic structure (double helix, nucleotides)? Where is it located inside cells (nucleus)? Why is it important?
  • Discuss the reading briefly to ensure comprehension.
  • Explain the goal: Today, we're going to actually *see* DNA by extracting it from fruit!

2. Lab Setup - Making the Extraction Buffer (5 minutes):

  • In a small cup, mix: 2 teaspoons of liquid dish soap, 1 teaspoon of salt, and 1/2 cup of water. Stir gently until the salt dissolves. This is your extraction buffer.
  • Explain the roles: Soap helps break open the cell and nuclear membranes (which are made of fats). Salt helps the DNA strands clump together.

3. Lab Activity - Extracting the DNA (20 minutes):

  • Place the chosen fruit (e.g., one large strawberry or half a banana) into the Ziploc bag.
  • Seal the bag, removing most of the air.
  • Thoroughly mash the fruit with your hands for about 2 minutes until it's a smooth pulp. (This breaks the cell walls).
  • Add 3 tablespoons of the prepared extraction buffer to the bag.
  • Reseal the bag and gently mix/squish the contents for another minute. Avoid making too many bubbles.
  • Set up the filtering apparatus: Place the sieve or coffee filter (supported by a funnel if needed) over the clear glass or jar.
  • Carefully pour the fruit mixture into the filter. Let the liquid drip through into the glass. You only need about 2-3 tablespoons of filtered liquid (filtrate). You can gently squeeze the filter to get more liquid, but try not to break it. Discard the pulp/filter.
  • Tilt the glass containing the filtrate slightly. VERY slowly pour about 1/4 cup of ice-cold isopropyl alcohol down the side of the glass so it forms a distinct layer on top of the fruit liquid. Do not mix!

4. Observation & Discussion (10 minutes):

  • Watch closely where the alcohol layer meets the fruit liquid layer. You should see white, stringy, cloudy stuff forming – that's the DNA! DNA is not soluble in cold alcohol, so it precipitates out.
  • Wait a few minutes for more DNA to become visible.
  • Gently use the wooden skewer or toothpick to spool (wind up) the DNA strands. Carefully lift it out to observe.
  • Discuss observations: What does it look like? Feel like (if you touch it - it's safe)? Why did we need cold alcohol? Where did this DNA come from?
  • Connect back to the reading: This substance holds all the instructions for making a strawberry (or banana, etc.).
  • Clean up the materials.

Extension (Optional): Research different methods of DNA extraction or famous scientists involved in discovering DNA's structure (Watson, Crick, Franklin, Wilkins).