You Sank My ... Bacteriophage?

Article excerpt

For the vast majority of the population, pipetting isn't a frequently used skill, but for one class period, the fate of a molecular biology experiment is determined by the skilled use of a $300 piece of equipment. Often the learning objective isn't the correct use of a micropipettor, but rather the steps that produce the amplified DNA band on a gel.

Over the past decade, our center has grappled with adequately training secondary science students and teachers to use micropipettes, trying to balance time spent practicing versus time investigating restriction enzymes or solving a crime using DNA gel electrophoresis. Because we often have students on campus for only a few hours, our goal is to provide an educational and enjoyable science experience that will hopefully leave a lasting positive impression.

Through the years, we have used most micropipetting practice procedures: Petri dishes with rows of wells, plastic gels, microfuge tubes, and colored water. When we switched to a bufferless electrophoresis system, we no longer had to worry about students puncturing their gels. The focus really could be on accurately using a micropipette to measure small volumes of liquid. The Battleship method--or "Pipetting by Coordinates"--was born.

Students are given a set of coordinates that correspond to the wells of a 96-well plate. Students use different volumes and colors of water to create a design in the plate. Eight designs are used by students and teachers in our precollege programs, all with success (see Figure 1 for sample design protocol). There are varying levels of protocol difficulty based on the number of volume changes and complexity of the design. All have volumes requiring the use of both a P20 and P200 micropipettor.

For our purposes, this activity is the perfect introduction to using a micropipette. Proper procedure is modeled by the teacher and then corrected individually while checking to make sure that students are only going to the first stop to draw up their sample. The satisfaction of seeing a design materialize (see Figure 2 for an example) is much more gratifying than moving tiny amounts of clear liquid from one tube to the next. Completed plates can be projected for the class to see and discuss. As an additional assessment, students can determine the total volume of liquid they added to the plate and the corresponding mass (1000 [micro]L water = 1 g) and, using a tared scale, determine the actual mass of the completed design. For example, the total volume for the bacteriophage design is 4462 [micro]L = 4.462 g. More than a 1-2% variance indicates a micropipetting error that needs to be investigated further. Possible causes could be going to the second stop before drawing up the sample, or a missed well. …