| Demonstration of Microscale Projection Experiments -
Chemistry en miniature Dische Reaction Peter Keusch |
Note: Animal cells like thymus and testes are a rich source of DNA. Thymus cells of the calf contain a large nucleus. The membranes of the cells and nuclei are lysed by treating with a surface-active agent (sodium dodecyl sulfate). When the membranes are disrupted the DNA of the nucleus can be isolated.
Hazards and safety precautions:
Safety glasses and protective gloves should be worn. Good ventilation required. DISCHE REAGENT should be prepared in a fume hood! Preparation of the experiment: 10 g of thymus placed into approx. 40 mL of tap water are cut finely with scissors. The suspension is filtered through a filter consisting of two layers of gauze. While stirring the filtrate, sodium dodecyl sulfate is added, until the filtrate becomes clear and viscous. The viscosity is caused by the liberated DNA. 10 mL dilute HCl are added to the viscous solution with stirring in order to separate the simultaneously formed proteins from the DNA. The precipitation of roughly cleaned DNA is filtered immediately and will be used for the test reactions. However, at first the DNA must be hydrolyzed. The precipitated DNA is dissolved in 2 M H2SO4 and the solution is heated for approx. 15 minutes in a boiling water bath. Experimental procedure: Three test tubes are set up as shown in the table below.
All three samples are mixed with 1 mL of DISCHE REAGENT and are placed afterwards for 5 - 10 minutes in a boiling water-bath.
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