Extracting DNA in your Kitchen

If the cell has a nucleus, the DNA is located in the nucleus.  If not, it is found in the cytoplasm.  DNA is the genetic material that has all the information about a cell.

DNA is a long molecule found in the formed by of two strands of genes. DNA carries two copies—two “alleles”—of each gene. Those alleles can either be similar to each other (homozygous), or dissimilar (heterozygous).

We’re going to learn how to extract DNA from any fruit or vegetable you have lying around the fridge. Are you ready?

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Materials:

• pumpkin OR apple OR squash OR bananas OR carrots OR anything else you might have in the fridge
• dishwashing detergent
• 91% isopropyl alcohol
• coffee filter and a funnel (or use paper towels folded into quarters)
• water
• blender
• clear glass cup

Download Student Worksheet & Exercises

Procedure:

Step 1: First, grab your fruit or vegetable and stick it in your blender with enough water to cover. Add a tablespoon of salt and blend until it looks well-mixed and like applesauce. Don’t over-blend, or you’ll also shred the DNA strands!

Step 2: Pour this into a bowl and mix in the detergent. Don’t add this in your mixer and blend or you’ll get a foamy surprise that’s a big mess. You’ll find that the dishwashing detergent and the salt help the process of breaking down the cell walls and dissolving the cell membranes so you can get at the DNA.

Step 3: Place a coffee filter cone into a funnel (or use a paper towel folded into quarters) and place this over a cup. Filter the mixture into the cup. When you’re done, simply throw away the coffee filter. Note: Keep the contents in the cup!

Step 4: Be careful with this step! You’ll very gently (no splashing!) pour a very small about of alcohol into the cup (like a tablespoon) so that the alcohol forms a layer above the puree.

Step 5: Observe! Grab your compound microscope and take a sample from the top. You’ll want a piece from the ghostly layer between the puree and the alcohol – this is your DNA.

What’s going on?

Veggies and fruits are made of water, cellulose, sugars, proteins, salts, and DNA. To get at the DNA, you first need to get inside the cells and separate it out from the other parts. The blender breaks up the fibers that hold the cells together.

The salt and detergent are added next so they can break down the cell walls. Cell walls of plants are made of cellulose. Inside that cellulose is another cell wall (cell membrane). This membrane has an outer later of sugar and an inner layer of fat.

The detergent is a special molecule that has an attraction to water and fats (which is why it works to get your dishes clean). The end of the molecule that is attracted to fat attaches to the fat part of the cell membrane. When you stir up the mixture, it breaks up the membrane (since the other end likes water). It wedges itself inside and  opens the cell up… which causes the DNA to flow out.

Since DNA dissolves in water, it stays in the vegetable juice. When alcohols is added, the DNA “comes out” of solution as the ghostly white strands seen at the bottom of the alcohol layer.

For Advanced Students:

For advanced students, here’s a set of videos that detail the cell walls, the basic biological molecules, DNA and RNA and how everything works together.

First watch this video below to see how we broke down the cell walls in the DNA extraction experiment:

Here’s a video on how DNA and RNA work:

Here’s a video that describes how the four biological molecules (proteins, lipids, carbohydrates, and nucleic acids) work:

Exercises

1. What are fruits and veggies made of?
2.  What does DNA stand for?
3.  What is DNA?
4.  What is a gene?
5.  Describe the structure of DNA.

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