DNA, or deoxyribonucleic acid, serves as the fundamental blueprint containing the instructions for life within every living organism. While often associated with complex laboratory procedures, the exciting truth is that you can extract DNA from common household items. Bananas are particularly well-suited for this engaging home experiment. Their soft texture simplifies the initial cell breakdown, and their polyploid nature means their cells contain multiple sets of chromosomes, resulting in an abundance of DNA that is easier to observe.
Gathering Your Supplies
You will need a fresh banana, dish soap, table salt, and rubbing alcohol (isopropyl or ethyl alcohol, ideally chilled beforehand). Additional items include a resealable plastic bag, a measuring cup and spoons, a small bowl, a coffee filter, a funnel (or another cup to hold the filter), and a clear glass or test tube.
Step-by-Step DNA Extraction
Begin by peeling half a banana and placing it into a resealable plastic bag. Carefully seal the bag, removing as much air as possible, and then mash the banana thoroughly for about two minutes until it forms a smooth, lump-free paste.
Next, prepare the extraction solution. In a separate small bowl, combine half a cup of water, one teaspoon of dish soap, and a quarter teaspoon of table salt. Stir this mixture gently to dissolve the salt without creating excessive foam. The goal is to avoid too many bubbles, as these can interfere with later steps.
Pour the prepared extraction solution into the plastic bag with the mashed banana. Reseal the bag and gently mix the contents for about one minute. Be careful not to create a lot of suds during this step.
After mixing, set up your filtration system. Place a coffee filter inside a funnel, or simply drape it over the rim of a clear glass or cup. Carefully pour the banana mixture from the bag into the coffee filter, allowing the liquid to slowly drip through into the collection vessel below. You can gently squeeze the filter to encourage more liquid to pass through, but avoid tearing the filter.
Finally, slowly pour an equal amount of very cold rubbing alcohol down the side of the glass, allowing it to form a distinct layer on top of the banana filtrate. Do not mix the layers.
The Science Behind the Process
The initial mashing of the banana serves a mechanical purpose, physically breaking down the rigid plant cell walls and the cell membranes. This ruptures the cells, allowing their internal contents, including the DNA, to be released into the surrounding mixture.
Adding dish soap introduces a detergent that plays a key role in the process. Cell membranes and the nuclear membranes that enclose DNA are primarily composed of lipids, which are fatty molecules. The detergent in the soap dissolves these lipid membranes, effectively breaking them apart and releasing the DNA from within the cell and its nucleus.
Table salt is then added to the mixture to assist in the DNA’s isolation. DNA molecules carry a negative charge due to their phosphate backbone. The positively charged sodium ions from the salt neutralize these negative charges, allowing the DNA strands to come closer together and clump. Salt also helps to keep other cellular proteins dissolved in the solution, preventing them from precipitating with the DNA.
The final step involves the addition of cold rubbing alcohol. DNA is soluble in water, meaning it dissolves readily in the aqueous banana solution. However, DNA is not soluble in alcohol. When the cold alcohol is layered on top of the mixture, it causes the DNA to precipitate, or solidify, out of the solution. The cold temperature further reduces the DNA’s solubility in the alcohol, enhancing the precipitation process and making it more visible.
Observing Your Extracted DNA
After adding the cold alcohol, you should observe a cloudy, whitish, stringy substance forming at the layer where the alcohol meets the banana mixture. This is the banana DNA, often appearing as delicate, translucent strands or a jelly-like mass.
To get a better look, you can carefully insert a toothpick or a thin stick into the white substance and gently twirl it. The DNA strands will often adhere to the stick, allowing you to lift them out for closer examination. Holding the stick against a dark background can make the DNA more distinct. While impressive to see, this extracted DNA is not stable for long-term storage and should be disposed of safely after observation. This simple experiment provides a tangible glimpse into the microscopic world of genetics.