Joseph D. Windham
Gladewater High School
Type of Entry:
Type of Activity:
This activity brings to the students the fact that there IS something called DNA and they are going to extract it from living cells.
Notes for the teacher are included in the actual lab.
There is very little preparation time involved. Getting to the meat market is the most inconvenient thing. Chilling of the alcohol can be accomplished by confiscating some ice from the lunchroom.
Class time is about 30-45 minutes. There is not much at this point that can be done with the material. The object is to SEE it.
Abstract of Activity
The activity of extracting DNA is a lab exercise originated by the Texas Biotechnology Teacher Enhancement Project (BTEP) 95. It is a quick, easy way of allowing lower level to higher level students set up a lab and actually see some DNA. It may be done in conjunction with lessons on DNA, or it may also be done in connection with a study on viruses and the lysogenic cycle of certain viruses. The detergent will lyse the cell and give the students a hands-on activity of how some viruses work.
Place a small piece of calf thymus (sweetbread from the local butcher) into a mortar. Use about a cubic centimeter. Cut the sample into smaller pieces using a scalpel or scissors.
Add 10 ml. of 0.9% sodium chloride solution (NaCl), and grind with the pestle for about 2-5 minutes.
Strain the solution through three or four layers of cheese cloth (available from your local fabric shop) into a test tube. Throw away the cheese cloth and keep the suspension.
Add 1.5 ml of 10% dish washing liquid (Dawn). 10 ml detergent in 90 ml water. The detergent lyses the cell membrane just like it removes grease from dishes.
Measure the total sample volume, then measure out two times that amount of ice cold 95% ethanol. Tilt your test tube and gently add the ethanol to the suspension by pouring the ethanol down the side of the test tube.
Using a clean, glass stirring rod, gently stir the mixture at the interface until the DNA begins to precipitate. It may start to precipitate as soon as you add the ethanol. Then twist the glass rod to spool the DNA sample onto the rod.
The precipitated DNA can be stored by transferring it to a fresh test tube or container containing 95% ethanol. Freeze indefinitely.