Deoxyribonucleic acid, or DNA, serves as the fundamental blueprint for all living organisms, guiding the development and function of every cell. Extracting DNA from fruit at home offers a hands-on opportunity to engage with basic biological principles. This accessible experiment demonstrates that science can be explored using everyday materials.
Gathering Your Materials
To begin your home DNA extraction, gather a few common household items. You will need a piece of fruit, such as a strawberry, kiwi, or banana; strawberries are particularly effective because they are octoploid, providing a greater amount of DNA for extraction. You will also need table salt, liquid dish soap (without conditioner), rubbing alcohol (isopropyl alcohol is suitable), a resealable plastic bag, a coffee filter or cheesecloth, and two plastic cups or small clear glasses. Ensure the rubbing alcohol is chilled in a freezer for at least 30 minutes before starting.
Step-by-Step DNA Extraction
Begin by preparing your fruit. Place about two strawberries, or a comparable amount of other fruit, into a resealable plastic bag. Carefully seal the bag, removing as much air as possible, then gently mash the fruit for about two minutes until it forms a smooth pulp.
Next, prepare the extraction solution. In a separate cup, combine two teaspoons of liquid dish soap, one teaspoon of table salt, and half a cup of water. Stir this mixture gently to avoid creating excessive bubbles. Pour this extraction solution into the plastic bag with the mashed fruit. Reseal the bag, removing excess air, and gently squish the contents for another minute to thoroughly mix the fruit and solution.
Prepare for filtration by placing a coffee filter inside a clean plastic cup, ensuring the filter creates a well. Carefully pour the fruit mixture from the bag into the coffee filter. Allow the liquid to drip through the filter into the cup below, separating the solid fruit pulp from the liquid filtrate. Avoid squeezing the filter, as this can force unwanted particles through. Once a sufficient amount of liquid has collected, remove the filter and discard the pulp.
Finally, retrieve your pre-chilled rubbing alcohol. Tilt the cup containing the filtered fruit liquid and slowly pour an equal amount of cold rubbing alcohol down the side of the cup. The goal is to create a distinct layer of alcohol floating on top of the fruit liquid. Within a few seconds, you should observe a white, cloudy, string-like substance forming at the interface between the alcohol and the fruit mixture. This visible material is the DNA.
The Science Behind the Extraction
Each step in this extraction process plays a specific role in isolating the DNA from the fruit cells. Mashing the fruit initially helps to break apart the plant tissue and rupture the rigid cell walls, releasing the cells’ contents.
The dish soap in the extraction solution acts as a detergent. Cell and nuclear membranes, which encase the DNA, are made of lipids. The detergent dissolves these fatty membranes, releasing the DNA into the solution.
Salt plays a dual role. It helps break down proteins bound to the DNA, keeping them dissolved. Additionally, the salt’s positively charged ions neutralize the negative charge of the DNA’s sugar-phosphate backbone. This neutralization makes the DNA less soluble in water, allowing the DNA molecules to clump.
The final step involves adding cold rubbing alcohol. DNA is soluble in water but much less soluble in alcohol. When the alcohol is carefully layered on top of the fruit extract, the DNA, now neutralized by the salt, will precipitate out of the watery solution. The cold temperature of the alcohol further enhances this precipitation by reducing the DNA’s solubility and slowing down enzymatic activity that could degrade the DNA.
What to Expect and Observe
After carefully layering the cold alcohol, you should observe a cloudy, white, stringy, or mucus-like substance forming at the boundary between the alcohol and the fruit layer. Strawberries, due to their polyploidy, often yield a more substantial amount of DNA.
To better observe the DNA, gently spool it by inserting a toothpick or a bent paperclip into the white substance and slowly twirling. The DNA strands will adhere to the tool, appearing like cotton candy or fine white threads. While this crude extract contains some impurities, it provides a tangible result of the molecular processes occurring within living cells.