LabBench Activity

Key Concepts II: Electrophoresis

In the 1960s, scientists discovered that bacteria have enzymes that cut, or "digest," the DNA of foreign organisms and thereby protect the cells from invaders such as viruses. Scientists have now isolated several hundred of these enzymes, known as restriction enzymes, or restriction endonucleases. Each is able to recognize and cut at a specific DNA sequence, known as a recognition sequence.

The discovery of restriction enzymes made genetic engineering possible because researchers could use them to cut DNA into fragments that could be analyzed and used in a variety of procedures.

In this part of the laboratory, you will use gel electrophoresis to separate samples of DNA that have been digested by restriction enzymes. Then you will compare fragments of unknown size to fragments of a known size to calculate the unknown fragment sizes.

Let's begin by looking at how restriction enzymes work.