Academic journal article The American Biology Teacher

A Visual Demonstration of Plasmid DNA Preparation from Bacteria

Academic journal article The American Biology Teacher

A Visual Demonstration of Plasmid DNA Preparation from Bacteria

Article excerpt


Unprecedented advances in unraveling mysteries of life have occurred as a result of the molecular biology revolution. Some major achievements of this revolution include new methods for the production of therapeutic compounds, insights into mechanisms of gene function and regulation, and the complete sequencing of the genomes of numerous organisms including humans. A critical foundation of this revolution is the ability to use the bacterium Escherichia coli (E. coli) as a factory to produce large amounts of virtually any DNA of interest by inserting it into a small, extrachromosomal circle of DNA called a plasmid. The ease and reproducibility of plasmid DNA isolation from bacteria permits numerous labs to conduct molecular biology experiments and greatly accelerates progress in understanding complex biological processes.

High school biology and introductory undergraduate biology or molecular biology classes frequently include labs in which students either isolate or manipulate plasmid DNA. Such labs often consist of a "cookbook" lab protocol that contains little, if any, information as to the purpose of the various steps involved in isolating the plasmid DNA. A major problem with this approach is that it leaves the procedure as a mysterious "black box" for most students. To assist in illustrating the roles of the different steps of the protocol, a model bacterial cell can be constructed with readily available materials and used in a highly interactive presentation that visually demonstrates the purpose of each step. This demonstration can be used as a stand-alone lesson when introducing recombinant DNA or it can be used as part of an introduction to a wet-lab experiment (a simple, rapid, low-cost, and highly reliable protocol is presented in the Appendix). The demonstration and the discussion related to it provide numerous opportunities to stress concepts included in the National Science Education Standards.

* Developing Student Interest

Why should I care? seems to be a common question in the minds of many students in introductory courses. Depending on the time available, the level of the students or their interests, a number of approaches can be used to help capture students' attention and engage them in class discussion. In high school freshman biology classes, we found that a means of introducing recombinant DNA technology and the role it can play in students' lives is to use an example of cloning a specific gene. Because of the prevalence of diabetes, a useful example is the cloning of the human insulin gene and the production of human insulin for therapeutic use in bacteria (Ladisch & Kohlmann, 1992). This example permits student involvement by questioning them about what they know about diabetes, the role of insulin in the disease, the health effects of this disease, or other areas the students or instructor want to develop. Since many students know someone with diabetes (in many cases they know a classmate who has diabetes or one of them may even suffer from the disease), this example provides an opportunity to get students to actively participate in discussion, regardless of their academic abilities.

An alternative introduction is to discuss consequences of sequencing the entire three billion base pairs of DNA of the human genome ( Genome/home.shtml). The current and potential uses of this technology in forensic science, health care, and business decisions are all areas that may be discussed depending on what focus the instructor wants to develop. Many students who are not normally interested in biological sciences become interested through discussions regarding possible uses of personal genetic information. Students are often surprised to learn that their ability to obtain health or life insurance or their employment may be affected by the DNA sequences they have inherited ( techresources/Human_Genome/elsi/elsi. …

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