Dean Saghafi-Ezaz

Benjamin Cardozo H.S., Queens, NY

Columbia University

Summer Research Program for Secondary School Science Teachers

August 1998


How can we extract human DNA ?

Materials: Diversity of Phenotypic expression of MELAS 3243 by Carolyn Sue, Eppendorf tubes 1.5 mL, 1X digestion buffer, Proteinase K (Sigma), Safety goggles, water bath at 37 degrees Celsius, forceps, bunsen burner. [Teaching Standard D- Make accessible science tools]

Motivation: How can you extract human DNA from a human? [9-12 Content Standard C- The Cell]

You can isolate human DNA from a person without having to manipulate bodily fluids, such as a hair follicle, blood, urine, saliva, etc.? (elaborate a little in class)


SAFETY NOTE: During this experiment USE SAFETY GOGGLES at ALL TIMES! [Teaching Standard D- Ensure safe working environment]

Take a blunt forceps and remove 3-6 hair follicles from your scalp.

Pipette 100 ul of 1x digestion buffer and 20 ug (2 ul of 10 mg/ mL) of Proteinase K into a 1.5 mL eppendorf tube.

Isolate the hair follicles by cutting the shaft away with scisssors and forceps, which are dipped in ethanol alcohol and passed through the flame of a bunsen burner.

Place the hair follicles into a labled 1.5 mL eppendorf tube and incubate the tube in a water bath at 37 degrees Celsius for 1 hour.

After the incubation, briefly centrifuge the tube to collect the evaporate and then heat the tube at 95 degrees Celsius for 10 minutes to inactivate the Proteinase K.

Let the tube cool off and then centrifuge the the tube at 13,000 rpm for 3-5 minutes.

Transfer the supernatant containing the DNA to a clean tube.

Label your tube and place it into the freezer until you are ready to use.

Summary Questions:

Why was the Proteinase K used? [9-12 Content Standard E- Understandings about science and technology]

Why did the Proteinase K become inactivated when heated for 10 minutes at 95 degrees Celsius?

How much DNA do you think is in your tube? How are you going to get an adequate amount of DNA from this sample ?

List 3 possible ways you think you could improve this experimental protocol. [Teaching Standard B- Orchestrate scientific discourse]


Return to Biology Lesson Plans Menu