DNA extraction lab
By. Maria Luiza Tavares
1. Introduction:
The deoxyribonucleic acid (DNA) is a molecule present in the cells' nuclei of all
living organisms, and it carries all their genetic information. It has millions of nucleotides
in its composition, which are constituted of three main parts: one deoxyribose (sugar),
one nitrogenous base, and one phosphate.
To know the structure of DNA and its characteristics is of extreme importance as
this molecule is responsible for the transmission of every genetic trait, and this
knowledge has the potential to develop research in various areas. The aim of this lab is
to introduce a DNA extraction technique, demonstrating the possibility of visualizing
DNA molecules agglomerated without the help of a microscope.
2. Materials:
● 2 cm of banana;
● Distilled water;
● Detergent;
● Salt;
● Fork;
● Sieve;
● Beakers;
● Test tube;
● Wooden stick;
● Cold ethanol (-20 oC).
3. Method:
a. Mash the banana in a Beaker with a fork;
b. Add 50 ml of distilled water;
c. Add 1 teaspoon of detergent and approximately the same amount of salt and stir
well;
d. Strain the mashed banana collecting the liquid in a clean beaker, then transfer
the liquid to a test tube, filling about 1/3 of the tube;
e. Gently pour the cold ethanol into the test tube. The volume of ethanol should be
about the same as the volume of “banana juice”;
f. Observe the interface;
g. Collect the DNA with a wooden stick.
4. Results:
The experiment started with the maceration. Followingly, the addition of distilled
water, detergent and salt had the objective of causing the lysis of the banana cells. The
resulting solution was filtered and transferred to a test tube. Ultimately, the addition of
the cold ethanol to the filtered mixture formed a DNA precipitate in the interphase in the
test tube.
5. Conclusion and Evaluation:
The extraction of DNA involves four main steps, which are: maceration, lysis of
the cells, removal of proteins in DNA fragments, and lastly the precipitation of the DNA.
Firstly, the maceration is important because it allows the solution of distilled water,
detergent and salt to easily reach the banana cells. The second step, which is the lysis
of the cell happens with the presence of the detergent, that breaks the lipidic bilayer of
the plasmatic membranes of the fruit cells (where the DNA is located). Furthermore, the
sodium chloride contributes with positive ions which neutralize the negative charge of
the DNA, and it is also fundamental to maintain the proteins dissolved. Finally, the
addition of the cold ethanol in the filtered solution contributes to the precipitation of the
DNA molecules, which have a low solubility in the alcohol.
This experiment can be replicated with other foods, such as: tomatoes, grapes,
onions and garlic. Especially in fruits, it is common to observe the precipitation of pectin,
a complex carbohydrate that is widely utilized in the sweets' industry. This molecule is
easily identified because of its jelly-like consistency. In contrast, the use of onion or
garlic guarantees more effective results, as they don't have pectin in their composition,
facilitating the visualization of the compacted DNA.
In conclusion, my replication of this experiment with bananas was well done. My
group followed the instructions correctly and we were able to observe the results that
were expected from the procedure. As an improvement, we could repeat the
experiment, but in the end, looking forward to identifying and differentiating pectin from
the actual DNA precipitate.
6. Works cited:
GONÇALVES, T. M. Extraindo o DNA de vegetais: uma proposta de aula prática para
facilitar a aprendizagem de Genética no Ensino Médio. Revista Educação Pública.
Website:
https://educacaopublica.cecierj.edu.br/artigos/21/15/extraindo-o-dn...-pratica-para-facilit
ar-a-aprendizagem-de-genetica-no-ensino-medio
Accessed in: September 7, 2024.
CRUZ, V.L.G. (UFPI); SOUSA, P.B. (UFPI); SOUSA, L.M. (UFPI); PASSOS, A.G.F.
(UFPI); LEAL, R.C. (UFPI). Extração do DNA da banana: aliando teoria e prática no
ensino de ácidos nucleicos em Bioquímica. 10o Simpósio Brasileiro de Educação
Química. Website: https://www.abq.org.br/simpequi/2012/trabalhos/219-13358.html
Accessed in: September 7, 2024.
MENEZES, A. LANGENDORF, C. MARQUES, L. MATTOSO, S. Extração do DNA da
fruta da banana. Website:
https://sites.unipampa.edu.br/pibid2014/files/2014/11/aula-pratica-extracao-do-dna.pdf
Accessed in: September 7, 2024.
