Extraction of DNA
DNA extraction is the laboratory technique to isolate or remove DNA (deoxyribose nucleic acid) from cells like blood, skin, the cornea of the 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 provided less quantity of DNA. But now many methods have sped up the extraction of DNA. These are either column-based or solution-based. 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 placed 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, cancer medicines are prepared using this technique.
FAQs about DNA Extraction:
- What is DNA extraction?
- DNA extraction is a laboratory technique used to isolate or remove DNA from cells, such as blood, skin, or bacteria.
- Who discovered DNA extraction and when?
- DNA extraction was first performed by Friedrich Miescher in 1869. He initially used lymphocytes but later switched to leucocytes collected from pus on surgical bandages.
- What method did Friedrich Miescher use for DNA extraction?
- Miescher used a method involving the addition of acid to the collected substance, followed by alkali, leading to the precipitation and dissolution of the substance, which he named “nuclein.”
- How has the method of DNA extraction evolved over time?
- From the complex and time-consuming methods of the 1950s, DNA extraction techniques have evolved to become faster and more efficient. Today, there are column-based or solution methods, as well as DNA extraction kits for easier use.
- What are the steps involved in DNA extraction?
- The steps include lysis or breakdown of cells, separation of DNA from cellular particles, precipitation of DNA using alcohol, cleaning or washing of DNA, and verifying the presence and quality of the DNA.
- How is DNA separated from cellular particles during extraction?
- DNA-associated proteins and cellular proteins are broken down using a protease, and precipitation of the proteins is facilitated by the addition of a salt. DNA is then found at the interface between the two phases after centrifugation.
- What applications does DNA extraction have?
- DNA extraction is used in various applications such as studying genetic expression, diagnosing genetic diseases, sequencing the genome, determining paternity, forensic analysis, replicating genes of interest, and preparing genetically modified organisms, hormones, vaccines, and medicines.
- How is the presence and quality of DNA verified after extraction?
- The existence of DNA can be confirmed by electrophoresis on an agarose gel with fluorescent dyes such as ethidium bromide, which reacts with DNA and can be visualized under UV light.
- What types of samples can DNA be extracted from?
- DNA can be extracted from various sources, including blood, tissues, hair, saliva, nails, skin, bacteria, viruses, fungi, and other biological materials.
- What is the purpose of lysis or breakdown of cells in DNA extraction?
- Lysis or breakdown of cells helps release DNA by breaking down cell membranes and nuclei, allowing DNA to be extracted from within the cells.
- How is DNA precipitated during the extraction process?
- DNA is precipitated by adding chilled alcohol (ethanol or isopropanol) to the DNA sample. DNA becomes insoluble in the presence of salt and alcohol, leading to its precipitation.
- Why is washing of DNA necessary after precipitation?
- Washing of DNA helps remove any contaminants or impurities that may be present in the sample, ensuring the purity and quality of the extracted DNA.
- What is the significance of verifying the presence and quality of DNA after extraction?
- Verifying the presence and quality of DNA ensures that the extracted DNA is suitable for downstream applications such as PCR, sequencing, or genetic analysis.
- How is DNA extraction used in forensic science?
- In forensic science, DNA extraction is used to analyze DNA samples collected from crime scenes, helping to identify suspects or victims and provide evidence for criminal investigations.
- What role does DNA extraction play in genetic engineering?
- DNA extraction is crucial in genetic engineering for isolating specific genes of interest, which can then be replicated, modified, or inserted into other organisms to produce desired traits or products.
- Can DNA extraction be performed on ancient or degraded samples?
- Yes, DNA extraction techniques can be adapted to extract DNA from ancient or degraded samples, although the process may require specialized methods and additional precautions to prevent contamination and degradation.