This demonstration can be used to help students visualize DNA by lysing (breaking open) bacterial cells on a slide and “stringing up” the DNA with a toothpick in less than one minute. It is most useful for grades 7-12. It requires minimal materials (bacterial cultures, glass microscope slides, 3% (w/v) potassium hydroxide (KOH), and wooden toothpicks). This technique can also be used to study bacteria because only Gram-negative bacteria lyse in 3% KOH; Gram-positive bacteria do not. The technique is equivalent to the Gram-stain reaction, but does not require a microscope or potentially messy stains.
University of Massachusetts, Amherst
Claudia A. Jasalavich