To do a DNA test, you will have to supple a sample of your DNA. But have you ever wondered how we get the DNA out of your cells to analyze it? Well let's dive into the incredible process of DNA extraction!
Without the ability to isolate DNA, fields such forensics, medical diagnostics, and agriculture would still be the dark ages. Fortunately, we have scientist Friedrich Miescher to thank for one of the most fundemental proceedure of molecular biology. Miescher performed the first DNA isolation experiment in early 1869 and since then many advancement have led the process of DNA extraction being streamlined. Today, scientist can extract DNA in as little as 20 minutes .
Before we dig deeper into the procedure of DNA extraction, let’s first briefly look at where the DNA is in the cell. In Figure 1, you will see some basic features of a cell but what you really need to know is that DNA is located in the nucleus that is surrounded by a nuclear membrane. There is also a small chunk of DNA located in mitochondria, but that's a topic for another day.
There are actually many methods to isolate DNA from a cell but for the most part there are three stages of the method. First is the break down both cellular and nuclear membranes, then the removal of cell debris and lastly, precipitate and purify the DNA. Here is how those three stages are done :
- Breakdown (or so-called lysis) of cell and nuclear membrane that is achieved by adding detergents.
- Removal of cell debris and proteins is done by adding proteases. Proteases are enzymes that digest proteins.
- DNA purification and precipitation are done by adding ice-cold alcohol ethanol or isopropanol.
DNA can be isolated from any living organism and the method used will depend on the sample type, the purity of the DNA, the amount of DNA and how the DNA will be analyzed in further experiments. For example, scientists would use a different method to isolate DNA from plant cells as compared to isolating DNA from a blood sample.
If we get a bit more technical, all DNA extraction protocols can be divided into two main groups comprising of many other techniques, chemical-based DNA extraction methods (solution-based methods) and solid-phase DNA extraction method (physical method).
Chemical or solution-based methods utilize many various chemicals. Based on the type of solvent used, methods can be divided into organic and inorganic. Organic methods use phenol or chloroform as a solvent. Inorganic methods use proteinase K or salts such as sodium chloride, potassium acetate, or ammonium acetate.
Solid-phase DNA extraction methods rely on the unique chemistry. One such technique uses magnetic beads, the magnetic field separates DNA. Positively charged magnetic beads attract negatively charged DNA. DNA is then washed and separated from the beads. Another technique uses filter papers or silica, a solid substance that binds DNA and aids in purification.
Scientists may either buy ready-to-use DNA extraction or develop and rely on their own DNA extraction methods. At BioCertica, we rely on the silica-column extraction method, and we will explain it in the next section.
How does DNA extraction method work?
In this article you will read about how BioCertica collects saliva samples and send them for analysis. If the sample passes a quality control check, then it is ready for DNA extraction using a silica-membrane-based method. The method is carried as follows:
- Extraction starts by adding a lysis buffer to the sample to burst the saliva cell membrane. At the same time, we add an enzyme protease to break down the proteins. This step is necessary to release the DNA from the sample.
- The first step also includes keeping the sample in a hot tube at 37° C. The sample should be occasionally mixed at high speed (this is known as vortexing). The purpose of this is that the lysis buffer and enzyme have maximum effect.
- The next step is to add highly concentrated alcohol followed by vortexing. This step helps the DNA aggregate and precipitate from the other particles in the sample (cellular debris and proteins).
- The sample is then transferred into a silica-membrane column tube and heavily centrifuged (rotated at very high speed). This separates fluids and particles of different densities. During this step, the heavy parts (cell membranes, proteins, and other particles) are sedimented through the membrane and accumulated at the bottom of the column tube. At the same time, DNA is "caught" on the silica membrane within the column tube.
- This is followed by a series of washing steps to obtain a high-quality DNA sample. The completely extracted DNA is retrieved from the membrane tube using an elution buffer.
From here, the DNA then undergoes a quality control check before it is prepared for genotyping. BioCertica is one more step closer to unveiling the wealth of knowledge that lies in your DNA.
DNA extraction is a fasinating process and the process is so simple you can even extract DNA from bananas in your own kitchen using household materials. Watch this video and channel your inner scientist for a fun and exciting DIY DNA extration.
Written by: Nermin Đuzić, M.Sc. in Genetics, Content Specialist
Peer-reviewed by: Edin Hamzić, Ph.D in Genetics, Chief Scientific Officer
- Tan, S. C., & Yiap, B. C. (2009). DNA, RNA, and protein extraction: the past and the present. Journal of Biomedicine and Biotechnology, 2009.
- Alonso, A. (2013). DNA Extraction and Quantification. Encyclopedia of Forensic Sciences (Second Edition). 214-218