Extraction of DNA
DNA extraction is the laboratory technique to isolate or remove DNA (deoxyribose nucleic acid) from the cells like blood, skin, the cornea of eyes, or from bacteria and viruses.
Discovery
DNA extraction was first done by Friedrich Miescher in 1869. Initially, he used lymphocytes but was not successful in drawing sufficient quantities. He then used leucocytes, which he collected from pus on fresh surgical bandages from a nearby clinic.
When Miescher added acid, he observed the precipitation of that collected substance. Then he added alkali and observed the dissolving of the substance. Thus, he called this substance “nuclein” as it was obtained from nuclei of cells.
After this, he developed a method for extraction from salmon sperm. He studied the extracted substance and observed that its chemical composition was different from proteins and other molecules. He also noticed that this substance played a vital role in the division of cells.
Method of DNA Extraction
From the 1950s the methods used for DNA extraction were very complex, time-consuming, and also provide less quantity of DNA. But now there are many methods that have sped up the extraction of DNA. These are either column-based or solution. Today, many DNA extraction kits are available with much easier use.
Steps involve in DNA Extraction
DNA can be extracted from plants’ cells, blood, hair, tissues, bones, saliva, nails, skin, etc. of humans or other animals. DNA can also be extracted from bacteria, viruses, and fungi.
Thus, all these things can be taken as a sample.
Lysis or Breakdown of Cells
The cells in a sample are separated from each other, frequently by physical means such as grinding or mincing and place into the solution containing sodium. The positively charged sodium ions in the salt aid safeguard the negatively charged phosphate groups that run along the foundation of the DNA.
A detergent is then added. The cleaning agent breaks down the lipids in the cell membrane and nuclei. DNA is released as these membranes are split.
Separation of DNA from cellular particles and other molecules
DNA-associated proteins, as well as other cellular proteins, may be broken down with the addition of a protease. Precipitation of the protein is assisted by the addition of a salt such as ammonium or salt acetate.
When the sample is minced with phenol-chloroform and centrifuged the proteins will stay in the natural phase and can be drained carefully. The DNA will be found at the interface between the two stages.
Precipitation of DNA by using Alcohol
Finally, chilled alcohol (either ethanol or isopropanol) is thoroughly added to the DNA sample. DNA is soluble in water however insoluble in the presence of salt and alcohol.
By carefully stirring the alcohol layer with a sterile pipette, a precipitate becomes visible and can be spooled out. If there is lots of DNA, you might see a stringy, white precipitate.
Cleaning/ Washing of DNA
Wash the resultant DNA pellet with chilled alcohol again and centrifuge for retrieval of the pellet. After pouring the alcohol off the pellet and drying, the DNA can be re-suspended in a buffer such as Tris or TE.
Verifying the presence and quality of the DNA
The existence of DNA can be confirmed by electrophoresing on an agarose gel consisting of ethidium bromide, or another fluorescent color that reacts with the DNA and checks under UV light.
Applications
- DNA extraction has many applications especially in biotechnology and forensic science.
- Extracted DNA is used in the study of genetic expression.
- It is used in diagnosing genetic diseases and disorders.
- Used in the sequencing of the genome.
- Used for determination of paternity.
- Criminals can be found out with the help of DNA extractions. (Skin, hair, nails, etc. at the crime scene are taken for this purpose).
- Extracted DNA is further used in replicating genes of interest either in plants, animals, or bacteria.
- Genetically Modified Organisms can be prepared from this.
- Different vital hormones (such as growth hormone) and vaccines, medicines for cancer are prepared using this technique.