The purpose of this lab is to have students extract DNA or Deoxyribonucleic Acid, from their own cheek cells. Cheek cells are collected with purified water and placed into a saline and soap solution. When alcohol is added, the DNA precipitates from the solution and thus the DNA is observable. This lab has been adjusted to use equipment and materials readily available within a secondary classroom and to fit within a 30 minute time period. Students will be able to see their own DNA from their own epithelial cells.
Can DNA be found in human eukaryotic cells? DNA, a polar molecule composed of two complementary chains of nucleotides wound in a double helix, is present in all living things from bacteria to plants to animals. In animals, it is found in almost all cell types: muscle fibers, reproductive cells, white blood cells, and skin cells; red blood cells do not contain a nucleus thus no nucleic DNA. The basic procedure for extracting DNA is the same, regardless of its source, although the specifics may vary:
Extracting DNA is a moderately simple process. The activity begins by collecting cheek cells by rinsing the mouth with purified drinking water and gently scraping the oral cavity with the teeth. This process will help gather numerous epithelial cells lining the oral cavity. A soap is then added to the cheek cell solution in order to split or break the cells open. This process releases the DNA from inside the cells and nuclei because the amphiphilic properties of the detergent break apart the fatty and protein components that make up cellular and nuclear membranes. A concentrated saline solution is then added to the cheek cell solution in order to change the polarity of the solution. This process will allow DNA, a polar or slightly negatively charged molecule by nature when released from nuclei, to dissolve in the ionic solution while many fats, carbohydrates and proteins settle out. Having a polarity is a major characteristic that allows the DNA to separate from the solution. Finally, the DNA is then precipitated from the ionic solution by the adding 70-90%+ isopropyl alcohol. This process will allow DNA, which is not soluble in the alcohol, and the alcohol, which are both less dense than the ionic solution, to appear towards the top of the solution. The density of DNA is also a characteristic of allowing it to separate from solution. The DNA will appear white and cloudy and/or thread-like during the precipitating period. The hypothesis for the procedure is that a collection of DNA can be extracted from human epithelial cells, isolated and observed.
Salt (Must be non-ionized “Canning Salt”) w/ spoon(s)
Liquid soap (ie Dawn) w/ 100 mL beaker
90% + Isopropyl alcohol “cooled”; 100 mL beaker to contain
Drinking or tap water
Electronic balance (with filter paper or weighing boat)
Methylene blue (optional)
Group: Note: All items list below should be sterile and properly clean before using for each step:
(2) 250 mL glass beakers
(1) 25 mL graduated cylinder
(1) 100 mL graduated cylinder
(1) test tube rack
(1) stirring rod
(1) test tube with lid or stopper x number of students / group
(1) paper cup (Dixie type) x number of students / group
Procedure: Note: Soap and saline solutions are to be used for both partners.
Optional: Add a few drops of “methane blue stain”. The stain will target DNA by bonding to the molecule due to its positive, flat, ringed characteristics.