The soft flesh of a banana provides a ready source of DNA. Using a few simple purification steps in a classroom setting, students can yield loads of crudely prepared DNA. To begin, the banana is mashed in a detergent/salt solution to lyse the cellular and nuclear membranes. Cellular lysate is strained, then the solubilized DNA is cleansed with a meat tenderizer (which contains an enzyme that breaks apart proteins). Lastly, ethanol is added to generate soft, white, globs of DNA and perhaps – with careful technique – slender threads that may be wound onto a glass rod.
By completing this activity, the student will:
1. have successfully extracted DNA from a banana, given the materials provided.
2. observe, handle, and describe a crude preparation of life’s hereditary material.
3. have the opportunity to use prior and newly acquired knowledge to draw conclusions regarding the structure and function of DNA.
4. have separated cellular components according to the standard scientific approach of exploiting chemical differences between the molecules of the cellular milieu.
Necessary Student Background
Students may have prior knowledge of DNA's structure and function. For students who have prior knowledge of the nature of DNA, the addition of cold ethanol at the end of the protocol provides an impressive moment when the white goo of DNA appears so suddenly and in such quantity. Contrasting starkly with the clear liquid extract from the cells, students may be pleased to be able to see for themselves this substance that they know to control life’s processes. For students who have no prior knowledge of the nature of DNA prior to beginning the activity, their own preparation of DNA may serve as an intriguing lead-in to a more conceptual discussion about the structure and function of the genetic material.
National Science Education Standards Addressed
Standard A: Science as Inquiry- In completion of this activity, students will investigate cell structure and the methods to extract DNA.
Standard C: Life Sciences- In completion of this activity, students will examine eukaryotic cell structure and investigate the function and the structure of DNA in living organisms. Students. Students explore DNA as being the molecular basis of heredity
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