Deoxyribonucleic acid, or DNA, is the genetic material containing the developmental instructions for every living organism. While often associated with complex laboratory work, isolating DNA can be performed easily using common household materials. This simple kitchen experiment allows for the visualization of the blueprint of life, which is otherwise too small to be seen without a powerful microscope. The technique uses physical and chemical steps to free the DNA from its cellular confinement and make it visible.
Gathering the Necessary Supplies
The extraction process requires several common household items. The alcohol must be chilled in a freezer for at least 30 minutes before the experiment begins to maximize its effectiveness. A measuring spoon and a stirring rod or skewer are also needed for managing the materials.
- One ripe banana for the biological sample
- A resealable plastic bag
- A coffee filter and two clear glasses or cups
- Liquid dish soap and table salt (sodium chloride)
- Cold rubbing alcohol (91% isopropyl alcohol or greater)
The Step-by-Step Extraction Protocol
Begin by peeling the banana and placing about one-third of it into the resealable plastic bag. Gently mash the fruit inside the sealed bag for approximately two minutes until it reaches a smooth, soupy consistency. This mechanical action helps to break apart the tough cell walls of the plant material.
Prepare the extraction buffer by combining two teaspoons of liquid dish soap, one teaspoon of table salt, and a half-cup of water in a separate cup. Stir gently until the salt is completely dissolved, being careful not to create a large amount of foam. Pour about two tablespoons of the buffer into the mashed banana bag, reseal it, and gently mix the contents for one minute. The goal is to evenly combine the buffer with the fruit material without generating excessive soap bubbles.
Place a coffee filter inside a clean glass, securing the edges to form a pocket. Carefully pour the banana slurry into the filter, allowing the liquid portion to slowly drip through into the glass below. This liquid, known as the filtrate, contains the banana’s DNA and other dissolved cellular components. You can gently squeeze the filter to speed up the collection of the filtrate.
Once you have collected a noticeable amount of filtrate, gently tilt the glass and slowly pour an equal volume of the ice-cold rubbing alcohol down the side. Allow the alcohol to form a distinct layer on top of the filtrate. It is important not to stir or shake the mixture. After a few moments, a cloudy, white, thread-like substance will appear at the interface where the two liquids meet. This visible material is the isolated banana DNA, which can be carefully spooled out using a skewer or thin rod.
The Science Behind the Steps
The initial mashing uses mechanical force to break down the rigid cellulose cell walls of the plant cells. This action is necessary to expose the internal cell structures where the genetic material is stored. The extraction buffer then chemically dismantles the cell.
The liquid dish soap contains detergents similar to the lipids that make up the cell and nuclear membranes. These detergents interact with the membranes, dissolving the lipid bilayers and causing the cell and nucleus to burst open, a process known as lysis. This action releases the DNA, along with other cellular contents like proteins and carbohydrates, into the surrounding solution.
The salt plays a dual role in preparing the DNA for the final precipitation step. DNA molecules possess a negative electrical charge due to the phosphate groups along their backbone. The positively charged sodium ions from the table salt bind to these negatively charged phosphate groups, neutralizing the DNA’s charge. This neutralization allows the long, stringy DNA strands to aggregate and clump together instead of repelling each other.
The final addition of ice-cold alcohol makes the DNA visible. DNA is highly soluble in the water-based filtrate because it is a polar molecule, but it is not soluble in alcohol. The combination of salt and alcohol causes the DNA to precipitate. Using chilled alcohol further reduces the solubility of the DNA, maximizing the amount that separates from the liquid mixture.