Agarose gel electrophoresis system in the classroom: Detection of DNA strand breaks through the alteration of plasmid topology

Good quality scientific teaching depends on the ability of researchers to translate laboratory experiments into high school and undergraduate classes, bridging the advanced and basic science with common knowledge. A fast‐growing field in biomedical sciences is oxidative stress, which has been associated to several diseases, including cancer and neurodegenerative disorders. We suggest herein a simple methodology for exploring DNA damage as an introductory pathway to these themes. The potential of natural or artificial products to induce DNA strand breaks can be easily tested in supercoiled plasmids incubated with selected products followed by agarose gel electrophoresis. This is designed to detect single and double strand breaks caused by reactive oxygen species generated by the products being tested. The altered topology of the damaged plasmid migrates slowly in the gel, creating a new band. We further introduce the quantitation of supercoiled DNA forms using densitometry of the gel with a digital camera; the values can then be used to estimate the number of breaks per genome using Poisson distribution. The system is inexpensive, rapid, and does not need high‐cost equipment and supplies and can be performed in high schools and undergraduate classes with a minimal structure.