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Starting From the Basics: DNA Extraction

BY: Farah Mahboob | Category: Biology | Submitted: 2010-07-16 07:59:20
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Article Summary: "Want to know how DNA is extracted? Listed is a simple procedure of DNA extraction plus some interesting and important facts about DNA..."


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What is DNA?
DNA, deoxyribonucleic acid is like a warehouse of information containing instructions that will be required for the development and function of a living organism.

How do I extract DNA?
DNA is present in the nucleus of our cells. Cells in different parts of our body have their own unique characteristic function due to their genetic material, that is the DNA. For example; Skin cell's DNA will be coding proteins that make your skin. Skin cells on your hands will be coding different proteins as compared to skin cells inside your cheeks which is smooth and moist, since it's being instructed by its DNA to constantly secrete mucous. Similarly hair cell DNA will be coding proteins that give hair its color and texture. For our experiment, we will be taking cheek cells which are the easiest to collect.

Step 1: Purifying DNA from Cells
Cheek cells are collected in a tube using a swab. A Lysis solution will be added in the tube. This solution will help in disrupting the cell membrane, entering the cell, disrupting the nuclear membrane, entering the nucleus and purifying our DNA from proteins and unwanted cellular material. So, the tube is then placed in warm temperature. Here the solution which contains detergent and Proteinase K (enzyme that digests proteins) come into action. The detergent will disrupt the cell and nuclear membrane where as the enzyme Proteinase K will free the DNA from its histones (proteins) around which DNA is tightly wrapped.

Step 2: Purifying DNA from unwanted cellular material
In this step a Salt solution is added to our DNA sample. Why are we using salt? Because salt causes proteins and other unwanted cellular material to precipitate and clump together. This of course further aids in our DNA purification. So our DNA sample with its salt solution is spun around at high speed in a centrifuge. Result; all the clumped unwanted cellular material sinks to the bottom of the tube while DNA rises to the top. DNA is then purified by carefully removing the top solution in the tube.

Step 3: Obtaining our DNA
Isopropyl alcohol is added. Since DNA is not soluble in alcohol it precipitates. This precipitated clumped DNA is now visible to the naked eye. Once again the solution is centrifuged which makes the DNA sink to the bottom of the tube. This DNA can either be used in further experiments using different solutions or it can be dried and stored in a freezer for any amount of time.

Step 4: Validating the presence of DNA
Presence of DNA can be confirmed through different procedures, for example;
1)Diphenylamine(DPA) indicator:
2)Electrophoresis on an agarose gel stained with ethidium bromide.
3)Measuring the absorbance of the DNA solution at different wavelengths.
4)Southern Blot technique.

How does DNA look like?
1. DNA is double helical.
2. Chemically DNA is made up of two long polymers of simple units called nucleotide. Nucleotides are attached to a back bone made up of sugar and phosphates.
3. Nucleotide base pairs are Adenine(A), Guanine(G), Thymine(T) and Cytosine(C). Adenine pairs with Thymine and Cytosine pairs with Guanine.
4. The two strands are anti parallel as they run in opposite directions and are twisted around one another forming a helix.
5. The torsion of helix and stepwise stacking of base pairs produces to major surface features on DNA, i.e., its major and minor groves.

How will DNA extraction help?
1. Genetic testing
2. Body identifications
3. Forensic Science

Facts about DNA:
1. Each cell contains about 2m of DNA.
2. DNA has an over all negative charge because of its phosphate backbone.
3. The arrangement and sequencing of base pairs along the length of a DNA is responsible for the unique characteristics of an organism. Thus, different combinations of base pairs produces variety in living organisms.
4. In DNA the amount of Adenine will always be equal to amount of thymine similarly, amount of Cytosine will always be equal to amount of Guanine (Chargaff's Law).
5. There are 10 base pairs in each complete twist of a DNA.
6. Nucleic acids (ATCG's) are heterocyclic aromatic organic compounds. Cytosine and Thymine are single ringed and called Pyrimidines. Where as, Adenine and Guanine are double ringed and are called Purines.

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