Carmen M. Simon Return to Biology Menu
South Shore High School, Brooklyn
of DNA from White Onion
Deoxyribonucleic acid (DNA) is the genetic material
of all organisms. It is the master
molecule in whose structure is encoded all information needed to create and
direct the chemical machinery of life (Micklos and Freyer, 1999).
Today, scientists can analyze DNA from minute samples
of blood, hair roots and saliva. Scientists
have all the tools needed to clone an extinct animal as a woolly mammoth that
was preserved in permafrost. The debated question is:
Scientists can determine why the legendary chemist,
John Dalton*, born in 1766 was colorblind by extracting DNA from his preserved
eyeballs. They can convict or
exclude rape suspects in the court of law, determine the sex and genetic
disorders of unborn fetuses, and create vaccines to prevent influenza pandemics
as the one of 1918 which killed 20 to 100 million people world-wide**.
Before scientists can study DNA, they must be able to
extract ( remove) the DNA from the tissue that encases it.
chromosomal DNA located within the cell?
organelles are mainly composed of 3 chemicals.
Using your textbook, determine the chemical composition of the cell
membrane. Draw a diagram of the Fluid-Mosaic
Model of Cell Membranes.
nucleotide is the basic unit of DNA. What
are the 3 chemical groups that make up a nucleotide?
Draw a diagram of a nucleotide.
You are a
scientist and you want to extract the DNA from your favorite pet so that you may
clone it. What steps would you take
to acquire pure DNA (no protein, no
lipids or carbohydrates) from your live pet?
Can DNA be extracted from an onion cell?
ml solution with 5 grams of Meat Tenderizer
1ml of dish-washing liquid
500, and 1000ml beakers
degree Celsius water bath
cold 95% ethanol
gram of chopped onion
* John Dalton proposed the atomic theory of matter.
That is, all matter is composed
of invisible entities called atoms. John
Dalton requested that his eyes be preserved after his death so that scientists
in the 18th century can determine the cause of his colorblindness.
Scientists in the 20th century determined the cause.
has killed 11.7 million people through 1997 (Kolata, 1999).
Time requirement: 50 minutes (~40 minutes if steps 1-3 are completed prior to class).
“X” every step of the protocol upon completion
____1. Mince onion.
____2. Heat 100 ml of meat tenderizer solution to 60 C using water bath.
____3. Add 50 g of onion to meat tenderizer solution. Stir and let sit for 15 min. at 60C.
____4. Remove beaker. Immediately place on ice for 5 minutes.
____5. Pour mixture into a blender.
____a. blend at low speed for 45 seconds. STOP
____b. blend at high speed for 30 seconds. STOP
____6. Pour mixture onto 4x folded cheesecloth draped over 500 ml beaker placed on ice.
____7. Gently squeeze off filtrate.
____8. Pour ~ 5 ml of filtrate into individual test tubes that are placed in ice bath. Let test-tubes rest at an angle.
____9. Pour ~10 ml of ice cold 95% ethanol down the wall of the test-tube.
____10. What do you see?
____11. When you see the stringy substance bubbling out of solution (that is the DNA), gently twirl the glass rod in the test-tube picking up the DNA.
____12. You have just extracted DNA. It can now be used for analysis or gene manipulation.
This laboratory exercise is designed to give you the opportunity to extract DNA from onion tissue. DNA was removed from the onion cells by heating the chopped onion; treating it with a soap, enzyme, and salt (meat tenderizer contains salt and enzyme). DNA was precipitated out of solution by using an alcohol (ethanol).
1. Why do you think you chopped and blended the onion? Do you think you could have removed the DNA using a whole onion with this protocol? Explain.
2. Why is detergent/soap used to wash a greasy pan that was used to cook a baked chicken/steak/fish?
3. What does a greasy pan that was used to cook a baked chicken/steak or fish have in common with a cell membrane?
4. Why do scientists use detergents to get clean DNA?
5. What happens when you place 2 negatively charged magnets near each other?
6. Sodium chloride (NaCl) ionizes in solution, i.e., NaClà Na+ + Cl-. How do you think the negatively charged phosphate groups of DNA will respond to the Na+ Cl- ions?
7. What importance does the enzyme have in this procedure?
8. If you had access to a high tech laboratory, what would you do with the DNA that was extracted from the onion?
a. What would be the benefits of your scientific investigation?
b. What would be the risks of you scientific investigation?
9. Create a story board explaining the protocol of extracting DNA from an onion. Be prepared to describe the protocol using the story board.
S2a- The student demonstrates an understanding of the cell.
S4d- The student produces evidence that demonstrates understanding of the impact of technology such as constraints and trade-offs; feedback; benefits and risks; and problems and solutions.
S5c- The student uses evidence from reliable sources to develop descriptions, explanations, and models.
S6a- The student uses technology and tools to observe and measure objects, organisms, and phenomena, directly, indirectly and remotely, with appropriate consideration of accuracy and precision.
S7a- The student represents data and results in multiple ways….
Columbia University Lesson Plan
Instructions Written by Mr. Edwin Klibaner
Dewey High School
Bozzone, D.M., 1999. A practical guide to the use of cellular slime molds for laboratory exercises and experiments. Department of Biology, Saint Michaels College, 10-11,18.
Kolata, G., 1999. Flu. Farrar, Straus and Giroux, New York, page 7.
Micklos, D. A. and Freyer, G.A, 1990. DNA Science.Carolina Biological Supply Company and Cold Spring Harbor Laboratory Press, 1 .