- Life Science
- Advanced Biology
Notes for teacher: This activity might introduce a reading or a lab about electrophoresis and restriction analysis.
Background required of students: Students should know that DNA is the primary genetic material in cells. They should be familiar with the double-helix structure of DNA and with how information is encoded in the sequence of bases. They should understand that DNA molecules are too small to study directly under the microscope, and that scientists have devised indirect ways of studying them.
Preparation time needed: 5 minutes to make signs and arrange chairs.
Class time needed: 10 - 15 minutes.
LESSON / ACTIVITY:
The purpose of the exercise is to help students picture what is happening at the molecular level during electrophoresis. Three students take the role of DNA pieces or fragments. Ask them what charge they carry. (Because they are deoxyribonucleic acid, they give off hydrogen ions in solution and carry a net negative charge.) The classroom becomes a gel bed. The chairs become agarose molecules in the gel. Tape, or have two students hold, "+" and "-" signs at opposite ends of the room to represent the positive and negative electrodes. The three students line up at the negative end of the gel tray (discuss why). When the electricity is "turned on" (a student holding a sign "Power Supply" shouts "Go!"), the DNA fragments run (or walk quickly) toward the positive electrode (discuss why). They must weave in and out of the desks. When the Power Supply yells "Stop!", the DNAfragments must freeze in their tracks. When the DNA fragments are all about the same size, it should be seen that they all reach the same place at about the same time, forming a band.
What would happen if a mixture of DNA fragments of different sizes were loaded into the gel? In a second run, small DNA fragments run next to large DNA fragments (2 students linking arms). When the Power Supply yells "Stop!", it will be seen that the smaller fragments have traveled farther than the larger fragments. Relate to gel pictures. Be sure that students understand that each band represents many, many DNA fragments of the same size, not just one fragment.
Materials needed: A classroom with separated desks or chairs arranged in a grid (I use 3 desks by 5 desks), "+" and "-" signs for the electrodes, and a Power Supply sign.
Evaluation: Students should be able to tell the numbers and relative sizes of different DNA pieces from a banding pattern in a gel picture.