All living organisms, from the smallest bacteria to complex plants and animals, contain deoxyribonucleic acid, or DNA. This remarkable molecule serves as the fundamental blueprint, holding all the instructions necessary for an organism’s development, function, and reproduction. While DNA is incredibly tiny at the cellular level, it is possible to extract and even see it with the naked eye from common living things. This article will guide you through a straightforward and engaging home experiment to isolate DNA from a strawberry.
Gathering Your Supplies
You will need several common household items. Prepare a few fresh or frozen strawberries, removing any green leaves. For the extraction solution, gather dish soap, table salt, and water.
Additional tools include a resealable plastic bag, a plastic cup or beaker, a coffee filter or cheesecloth, and measuring spoons. Acquire cold rubbing alcohol, chilled in a freezer to enhance results.
Step-by-Step Strawberry DNA Extraction
The process of extracting DNA from a strawberry begins with mechanical disruption. Place a few destemmed strawberries into a resealable plastic bag and gently mash them for about two minutes, aiming for a smooth, pulpy consistency. This initial mashing helps to break apart the strawberry’s cells, an important first step in releasing the DNA from within.
Next, prepare the DNA extraction solution by combining two teaspoons of dish soap, one teaspoon of table salt, and half a cup of water in a separate cup. Once mixed, pour this solution into the bag containing the mashed strawberries. Reseal the bag, remove any excess air, and gently mash the mixture again for another minute, being careful to avoid creating too many soap bubbles.
After the second mashing, set up your filtration system. Place a coffee filter or a piece of cheesecloth inside another clean plastic cup, ensuring it lines the cup fully. Carefully pour the strawberry mixture from the bag into this filter, allowing the liquid to slowly drip through into the cup below. You may gently press the solids in the filter with a spoon to encourage more liquid to pass through, but avoid tearing the filter. This step effectively separates larger solid debris from the liquid containing the dissolved DNA.
Finally, precipitate the DNA. Tilt the cup containing the filtered strawberry liquid and slowly pour an equal amount of cold rubbing alcohol down the side, allowing it to form a distinct layer on top of the strawberry liquid. Avoid mixing the two layers.
Within a few seconds, you should observe a white, cloudy, or stringy substance beginning to appear at the interface where the two liquids meet. This visible material is the strawberry DNA clumping together. You can then gently spool this DNA onto a coffee stirrer or similar tool by rotating it at the interface of the two layers, lifting the extracted DNA out of the solution.
Understanding Your Results
Observing the extracted DNA reveals the processes within cells. The initial mashing of the strawberries physically breaks open the cell walls and cell membranes of the strawberry cells. These barriers must be disrupted to access the cellular contents, including the nucleus where the DNA resides.
Dish soap in the extraction solution breaks down cell membranes. Cell membranes and nuclear membranes are primarily composed of lipids, which are fatty molecules. The detergent dissolves these lipid membranes, causing cells to burst open (lyse) and release their internal components, including DNA, into the solution.
Salt neutralizes the negative charges on DNA molecules. DNA has a negatively charged sugar-phosphate backbone, and salt ions, such as sodium, bind to these charges. This neutralization allows the DNA strands to come closer together instead of repelling each other, making them less soluble in water and aiding in their eventual precipitation. Additionally, salt helps to separate proteins that are bound to the DNA and keeps them dissolved, preventing them from precipitating along with the DNA.
Filtering separates larger, insoluble cellular debris, like cell wall fragments and pulp, from the dissolved DNA and other smaller molecules. This ensures that only the dissolved components pass through, leading to a cleaner DNA sample.
Finally, cold rubbing alcohol makes the DNA visible. DNA is soluble in water but not in alcohol. When alcohol is layered on the solution, DNA precipitates, clumping together to form a solid, visible mass, often appearing as a white, cloudy, or stringy substance. The cold temperature further reduces DNA solubility, enhancing precipitation and visibility.