Bacteria come into contact with foreign DNA in a variety of ways. For instance, viruses can infect bacteria, and when they do, they inject their genetic material, or DNA, into the bacterial cell. As a protective mechanism, the bacteria use enzymes that degrade the foreign DNA, called restriction enzymes, to destroy the invading genetic material.
DNA Basics
DNA, which stands for deoxyribonucleic acid, is genetic material. Cells use their DNA to make proteins, and the information encoded into DNA dictates how a cell is shaped and how it functions. Drs. Reginald Garrett and Charles Grisham explain that viruses, unlike bacteria and other organisms, don't have the machinery to convert their genetic information into products. Therefore, they must invade other cells, like bacterial cells, inject their DNA and then take over the cell's machinery to reproduce.
Bacterial Invasion
When a virus infects a bacterium, it first binds to the outside of the bacterial cell. It then injects its DNA into the bacterium. If the bacterial cell allows the viral DNA to remain, it will take over the cell to the extent that the bacterial cell can no longer produce any of its own cellular products, nor can it reproduce. The virus will use the bacteria's machinery to make many copies of itself and will then cause the cell to rupture, freeing the new viruses. Drs. Garrett and Grisham note an infected bacterium will inevitably die unless it deals with invading viral DNA.
Restriction Enzyme Features
An enzyme is simply a molecule, generally a protein, that helps a chemical reaction happen more quickly than it otherwise would. Digestive enzymes, for instance, allow the human digestive tract to break down food quickly. Restriction enzymes break down DNA into smaller, nonfunctional parts. The enzymes do this by inserting molecules of water into the DNA chain, explains Dr. Joan Brooks in a 1987 paper in the journal "Methods in Enzymology." Wherever a molecule of water joins the DNA chain, the chain splits into two parts.
Restriction Enzyme Applications
One important feature of restriction enzymes, notes Dr. Brooks, is that they break DNA chains at specific places rather than randomly. This means that researchers can use enzymes that have been isolated from bacteria to break down sections of DNA and move pieces of the DNA from one organism to another. This is useful, because it allows researchers to confer specific traits common to one type of bacterium upon another.
Medical Applications
Researchers can even use restriction enzymes to move traits from human cells to bacterial cells. For instance, individuals with type 1 diabetes must take the protein hormone insulin on a regular basis, explains Dr. Gary Thibodeau in his book, "Anatomy and Physiology." Insulin is expensive to make in the lab, but it's possible to insert a small portion of human DNA isolated using restriction enzymes into bacterial cells. The cells then become "infected" with the insulin gene and begin producing insulin that can be collected for use in humans.
References
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
- "Methods in Enzymology"; Properties and Uses of Restriction Endonucleases; Joan Brooks; 1987
- "Anatomy and Physiology"; Gary Thibodeau, Ph.D.; 2007
