Activitat

DNA extraction from human buccal epithelial cells.

Personatges:

Rosalind Elsie Franklin

Tema: Nucleic Acids

Competències

Competència Matemàtica, en ciència, tecnologia i enginyeria

Competència personal, social i aprendre a aprendre

Matèries i cursos per Sistema Educatiu

Espanya > Biologia i Geologia > 4t ESO > Genètica i evolució

Enunciat

<img title="Women's Legacy logo" src="//inclusion.womenslegacyproject.eu/images/LogoWL.svg" /><hr />Rosalind Franklin has gone down in history as the author of the famous photograph 51. An image of the DNA molecule taken with a technique that was absolutely novel at the time: X-ray diffraction. As both Watson and Crick recognised years later, Rosalind Franklin's vision of the image was fundamental in the discovery of the structure of DNA.&nbsp; DNA is found in the nucleus of cells, bound to proteins called histones. The DNA-protein complex is called chromatin. &nbsp; Nowadays, it is very common to carry out different types of tests in forensic medicine as well as in clinical medicine, for which it is necessary to extract DNA from cells. Once extracted, we can check whether the genetic sequence corresponding to a certain disease we are looking for is present or not, or whether certain genetic sequences in the sample match or do not match those present in police evidence (e.g. blood, hair or semen collected at a crime scene).&nbsp; When DNA extraction is done in a laboratory, it has to be done very carefully in order to separate the nuclear DNA from the other DNA (e.g. mitochondrial DNA) that may be present in the cell. In addition, it has to be obtained as pure as possible (i.e. free of proteins etc.).
On the other hand, DNA is very labile, i.e. it is easily broken, both by physical methods (rough shaking, etc.) and chemical methods (presence of Dnases in the hands, for example), so one of the basic rules when working with DNA is to wear gloves so that the Dnases in the hands do not break the DNA we are working with and to be very careful when handling it.&nbsp; We are not going to take so many precautions, as we are not going to use the DNA for sequencing, etc., so the result of our extraction will be a very contaminated and dirty DNA, without purification; however, the DNA strand will be visible in the test tube, which will achieve the objective of this practice. &nbsp;The cells of the buccal epithelium are easily detached just by rinsing your mouth, so this is an easy way to obtain DNA from the nuclei of these cells.&nbsp; We break the nuclei of these cells using a hypertonic solution (with a lot of salt) and empty the contents into the solution. As the nuclei of the cells contain RNA and proteins, among other things, we try to separate the DNA from other substances as far as possible. This is achieved with the detergent.
MATERIAL&nbsp; -Distilled water.&nbsp; -Common salt.&nbsp; -Liquid detergent or shampoo.&nbsp; -Sodium bicarbonate.&nbsp; -96&ordm; ethyl alcohol.&nbsp; -Epithelial cells.
REALIZATION&nbsp; 1.- Prepare a buffer with the following ingredients and keep it in the fridge or in a crushed ice bath: &nbsp; &nbsp; &nbsp; &nbsp;-120 ml of water, if possible distilled and if not mineral. Do not use tap water. &nbsp; &nbsp; &nbsp; &nbsp;-1.5 g table salt, preferably pure. &nbsp; &nbsp; &nbsp; &nbsp;-5 g baking soda. &nbsp; &nbsp; &nbsp; - 5 ml of liquid detergent or shampoo. &nbsp;
2.- Take 15 ml of buffer and put it in a glass.&nbsp; Put about 20-25 ml of water (one tablespoon) in your mouth and rinse well, moving the water from one cheek to the other. Spit the water into the glass where the tampon is. &nbsp; 4.- Stir gently to mix the two solutions, but do not shake, to avoid foaming.&nbsp; 5.- Pipette 15 ml of alcohol (it must be cold. If it is not, it may not come out well). The alcohol should carefully slide down the walls of the beaker. This is very important so that the DNA does not break.&nbsp; 6.- Stir the beaker gently until you see a precipitate appear. DNA is not soluble in alcohol, so it precipitates in the form of "threads" that can be observed with the naked eye and collected with a rod or a hook.
QUESTIONS&nbsp; 1.- What does the DNA obtained look like?&nbsp; 2.- Why did we use salt? Reason the answer.&nbsp; 3.- What about the alcohol? Reason the answer.&nbsp; 4.- Look up information about Rosalind Franklin: How did the images of the DNA get into the hands of Watson and Crick? Did these scientists recognise the work done by Franklin? Why do you think this was the case?&nbsp; 5.- Write down your conclusions.

Observacions i context

Rosalind Franklin was a contemporary of the British nutritionist Elsi Widdowson and the Austrian physicist Lissa Meitner.
Like Mary Anning, the English palaeontologist who discovered the first ichthyosaur, plesiosaur, and dinosaur coprolites, Rosalind found it very difficult to research and publish because she was a woman. In both cases, their male colleagues used their findings to achieve success in their research. In the case of Mary Anning, she could not publish her findings because she was a woman and her name always appeared behind a male name. In the case of Rosalind Franklin, her "photography" was key to the discovery of the double helix, but the recognition went to Watson and Crick, who received the Nobel Prize.

Descripció

Learning situation. This is a laboratory practice. It is advisable to divide students into groups of three or four people to carry out the activity.
Objectives:
-To obtain DNA from cells in the mouth and observe it.
-To learn how to work in a molecular biology laboratory.
-To learn how to make solutions.
-Understand that scientific activity is a human activity in a social context, in which things like what happened to Rosalind Franklin can happen.
Specific competences: CE1, CE3, CE4, CE7.
Timing: One session to carry out the practical and another (which can also be done by the students at home) to answer the proposed questions.
Spaces/Resources needed: Biology laboratory. Laboratory material indicated in the practical script.
Evaluation criteria:
-To be able to follow the guidelines indicated in the script to obtain results.
-Correctly measure volumes and carry out the necessary calculations.
-Use laboratory equipment appropriately.
-To argue conclusions in a coherent way using appropriate language.
Curricular evaluation of students:
Students will be assessed, on the one hand, on the basis of a Sel-assessment rubric and, on the other, according to the diligence in the execution of the practice and attending to the relevance of the answers offered. The evaluation will be group-based, if it has been decided to organise the activity in groups.

DNA extraction from human buccal epithelial cells.

Enunciat

Observacions i context

Descripció

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