DNA Isolation

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Posted By : ScienceIndia Administrator

Deoxyribonucleic acid, more commonly known as DNA, is a complex molecule that contains all of the genetic material or information necessary to build and maintain an organism. All living things have DNA within their cells. Most DNA is located in the cell nucleus (where it is called nuclear DNA), but a small amount of DNA can also be found in the mitochondria. The information in DNA is stored as a code made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T).

Human DNA consists of about 3 billion bases, and more than 99 percent of those bases are the same in all people. The order, or sequence, of these bases determines the information available for building and maintaining an organism. DNA bases pair up with each other, A with T and C with G, to form units called base pairs. Each base is also attached to a sugar molecule and a phosphate molecule. Together, a base pair, sugar, and phosphate are called a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix. The structure of the double helix is somewhat like a ladder, with the base pairs forming the ladder’s rungs and the sugar and phosphate molecules forming the vertical sidepieces of the ladder.

There are different forms of DNA known as the double stranded and single stranded DNA (dsDNA and ssDNA). Double-stranded DNA consists of two polynucleotide chains. Within this arrangement, each strand mirrors the other as a result of the anti-parallel orientation of the sugar-phosphate backbones, as well as the complementary nature of the A-T and C-G base pairing. Single stranded DNA Is a DNA molecule consisting of only a single strand contrary to the typical two strands of nucleotides in helical form.

DNA was first observed by a German biochemist named Frederich Miescher in 1869. But for many years, researchers did not realize the importance of this molecule. It was not until 1953 that James Watson, Francis Crick, Maurice Wilkins and Rosalind Franklin figured out the structure of DNA, a double helix, which they realized could carry biological information. From then on, DNA has been the key to information on human ancestry, diseases and genetic enhancement.

To obtain pure DNA samples a common technique known as DNA isolation is used. DNA isolation is a process of purification of DNA from sample using a combination of physical and chemical methods. Friedrich Miescher did the first isolation of DNA in 1869.

It involves separating all nucleic acid in a cell away from proteins, fatty acids and other cellular materials. The main principle behind DNA isolation is lysis or breakdown of materials, or in the case cellular matter. DNA can be isolated from all types of living or fossilized cells containing a nucleus or nucleoid e.g. Blood, skin, hair, nails, saliva, and bacteria. To summarize the process, the main 4 steps of DNA isolation are Lysis, phase separation, clearing of proteins and precipitation of the DNA. First, chemicals are used to break the cell membranes and expose the DNA along with the cytoplasm within the cell. For cells having a cell wall cellulase is used. Lipids, extra cellular debris and other organic substances present in the cell are separated from the genetic material using detergents and other enzymes. The proteins present in the solution are also broken down using a chemical known as protease. The solution is treated with certain chemicals to make unwanted debris such as broken lipids and proteins to separate from the DNA and clump together. After this is removed, the final solution is centrifuged and a DNA pellet is precipitated. The DNA can then be purified with an ethanol wash and air-dried. After the end product i.e. DNA pellet is ready, it can undergo qualitative and quantitative experiments i.e. electrophoresis and DNA quantification respectively.

The information extracted from the DNA can then be used for several real life applications. A major area of DNA research is that of genetics and medical research. It allows us to easily diagnose several diseases and better assess a person’s susceptibility to a genetic disease. DNA has also been very important in the field of forensic science with techniques like DNA fingerprinting. DNA has also created an impact in the field of agriculture by allowing breeders and scientists to breed different species of plants and animals to make new and improved versions of said species. In this way DNA plays a key role in the progress and the development of the future of a vast number of scientific fields.

Author: Ekta Ramesh, Gems Modern Academy, Grade 10

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