Method for DNA Extraction

By Richard Hoyt
A model of DNA
Image by, courtesy of Pål Berge

All living things, animals and plants, contain DNA (deoxyribonucleic acid) that determines the characteristics that are passed on from one generation to the next. No two living things contain identical DNA, except twins that came from one separated ovum, or egg cell. Extracting a sample of DNA sounds complicated, but the process that has evolved over the years is surprisingly simple.


DNA is the physical means by which biological characteristics are passed on, the evolutionary process first described by Charles Darwin in his seminal book "On the Origin of Species" in 1859. In 1953, James D. Watson and Francis Crick discovered the structure of DNA. In 1962, Watson, Crick and Maurice Wilkins were awarded the Nobel prize in medicine for their research into DNA. In 1968, Watson published "The Double Helix," his bestselling book on the competition by scientists to be the first to describe DNA.

DNA Profiling

The DNA in every human is 99.9 percent identical. The genetic profiling, or identifying the individual characteristics of a person, is based on the remaining .1 percent that is different. Sir Alec Jeffreys developed the technique of profiling DNA at the University of Leicester in 1984. That technique is the basis of national DNA databases and is used in criminal investigations involving semen, skin, sputum and other biological samples.

Genome Sequencing

The DNA used for criminal identification is from the nucleus of the cell. It is also used in genome sequencing to learn the relationship of genes in an organism. Since the possible sequences are so large, they can only be charted through the use of computers.

Mitrochondirial DNA

Cells also contain what are structures called mitochondria that convert energy into a form that cells can use. Mitrochondrial DNA is passed on by females. Mitochondrial DNA is used to trace ancestry, and is currently being used by researchers studying the origin and spread of different races of humans.

Extracting DNA

The cells first have to be disrupted, or "broken open," to expose the DNA. This breaking down of the cell membrane is called lysis. Crime and medical research laboratories often use an ultrasound device to separate the cells by vibrating them. A blender can do the same thing.

Removing Fat and Proteins

After the cells are separated by vibrating or blending, the membrane lipids have to be removed. Lipids are sterols, fats and waxes. They form most of the fat in the human body and are insoluble in water. Both research scientists and students use detergent to remove the lipids; they literally "wash" the separated cells. Protective proteins are molded and folded around the nucleus of the DNA cell. A naturally occurring enzyme called a protease is ordinarily used to break down the proteins. Enzymes found in meat tenderizer, pineapple juice or the solution used to clean contact lenses can be used.

Turning Into Solids

As the cold alcohol is added, long, stringy molecules rise to the top of the solution. These are DNA molecules. As they rise into the cold alcohol, the cells form stringy clumps. Researchers collect these strands of DNA with a lab straw and use a microscope to identify or study them.

About the Author

I am interested in anything to do with writing and editing suspense fiction, mysteries, thrillers and plot and narrative-based novels. Since I have a PhD in American studies, my interests are wide ranging, including issues of the environment, public policy, the right of women to have abortions, the need for the regulation and reform of the financial industry. I am a political liberal, most comfortable with issues that reflect the need for constructive change in our country. I am interested in anything having to do with people learning to live more simple, less consumer-driven lives. I am interested in the larger topic of food and cooking, although I am no expert. I am also well traveled, having spent twenty years writing novels while living abroad. I am an agnostic and have a special interest in maintaining the separation of church and state. I am well read. I regard researching, learning and writing as a form of entertainment. I have eclectic interests. I am curious.