How to extract DNA from a banana

This is one of the most popularly known processes to extract plant genetic material and be able to observe it under a microscope. It can also be made with tomatoes, passion fruit or other fruits. A banana is used, in this case, due to the simple way of handling it and the few steps required to crush it in our experiment.

To extract DNA from a plantain or banana, you need:

• A plantain or banana.
• A very sharp knife.
• A fork or a potato masher.
• Liquid detergent or laundry soap.
• Mineral water.
• A little bit of salt.
• Sodium bicarbonate.
• A funnel.
• Kitchen paper or paper filters.
• Very cold alcohol.
• Containers of any material to carry out the steps. One will be needed for the mashed banana and another for the soap and sodium. It is helpful if you make the final mix in a clear container where you can easily see the contents from the outside.
• Glass or plastic straw, preferably transparent. Alternatively, it is also a good idea to have a knitting needle with a hook point on hand.

Remember to avoid using utensils that could be contaminated to crush the fruit. A cheese grater, for example, could have traces of fat when used, and we don’t want these to contaminate the final sample.

Steps

• The first step will consist of cutting the banana into small pieces. Next, it is convenient to crush the banana so that it is a puree. By doing this you will be breaking the cells of this fruit, which contain the DNA.
• Taking into account that cells are generally covered by a lipid membrane, we will need an additional method to break them more thoroughly. For this, in the next step we will make a solution in a separate container. This solution is often called lysis buffer in academic chemistry circles.

To make the lysis buffer we must take liquid or laundry soap and a cup of mineral water, and dilute it. If it is the liquid, two jets of it will suffice to color the water. If it is powder detergent, a heaping tablespoon will suffice.

The detergent will carry out the function of dragging lipids (which are a type of fat) and proteins (a type of essential macronutrient) that are soluble in lipids. We must also add to this mixture two teaspoons of salt and six teaspoons of baking soda. The sodium in these two compounds, with its positive ions, facilitates the integrity of the strands that make up DNA. The bicarbonate in particular will be in charge of neutralizing the pH of the solution, to prevent the DNA from being damaged. The DNA strands are now unprotected because they have been stripped of the lipids that used to coat them.

• We will now resort to a physical separation method. What we need to do is add to our detergent solution the biological material that we extracted in step 1. We take four tablespoons and mix them for at least three minutes, with a maximum of five minutes.

With the kitchen paper or the coffee filters as a rudimentary filter and the help of a funnel, we place one of these filters in the funnel and pour the liquid of our mixture into the container. It will be from this mixture that we will finally extract the DNA sample to be observed. 

At this point we will have our solution in an aqueous phase and we can easily collect our genetic material. The solution contains RNA, DNA, and some proteins that are soluble in water.

chemical separation

Now we will explain the chemical separation method, taking advantage of the chemical characteristics of the molecules of the biological material that we will be separating. We will use 5 ml of the solution that we have just filtered. We mix with an amount of cold alcohol that triples it in volume, in this case, 15 ml. The cold temperature of the alcohol will guarantee a better performance of the method. Because the part of the biological solution that contains DNA is not soluble in alcohol, we will see how it agglomerates and separates from the other elements, forming a layer that is easily recognizable with the naked eye.

It is important to consider that the alcohol must be added slowly, preferably by sliding it along the edges of the container where the aqueous solution is waiting. We’re also trying not to damage the DNA, which we might want to look at under a microscope later.

Now that we can distinguish the cloudy solution that carries the DNA of our sample, we will proceed to extract it from the aqueous medium. We take the straw and introduce it into the aqueous medium until it touches the previously prepared solution. Immediately afterwards, we cover the outer end of the straw with a finger in order to cover the air leak and that it serves to hold the solution. If we are unable to get the solution to adhere to the tip of the straw, we extract it without ever removing our finger from the other end and proceed to repeat the process, making sure that the straw has at least visibly entered the dense medium containing the material. genetic. We place our finger at the opposite end, covering it well, and try little by little to extract this medium from the aqueous solution, slowly moving the straw outwards.

It is likely that we will have a hard time catching this last solution, so if we do not succeed with the previous method, we could use the knitting needle with its hook point downwards to extract this thick part of the solution from the aqueous medium.

We now have our plant DNA solution ready to be viewed under a microscope. It is recommended to immediately place it in a Petri dish or similar utensil to avoid contamination.

References

Educate and Create. (s/f). How to extract DNA from a plant? Available at: https://www.educaycrea.com/2015/09/como-extraer-el-adn-de-un-vegetal/

Ochoa, J. (2010). DNA extraction with kitchen material. Available: https://www.youtube.com/watch?v=PkjtFM_UVxk&t=243s