DNA Extraction from Wheat Germ
Materials











Raw wheat germ – 1 level teaspoon
Liquid detergent - 1 ml
Ethyl Alcohol (95%) – 15 ml (COLD) on Ice
50o – 60o Celsius tap water – 20 ml
Hot plate with Beaker of Tap Water
Thermometer
2 - 50 ml beakers
1 - Graduated cylinder (large)
Glass stirring rod for stirring mixture
Paper towel or Eye dropper – may be needed to remove foam
Paper clip hook or wooden stick or spaghetti for collecting DNA
PROCEDURE:
1. Place 1 LEVEL teaspoon of raw wheat germ in a 50 ml beaker
2. Add 20 ml of hot (50-60 °C) tap water and mix constantly for 3 minutes.
3. Add 1 ml or (15 -18 drops) of detergent and mix gently for 5 minutes. DO NOT MAKE FOAM
4. Use a piece of paper towel or an eyedropper to remove any foam from the top of the solution.
5. BEFORE adding the alcohol, POUR the water/detergent solution into a clean beaker, leaving
behind the wheat germ.
6. Tilt beaker with the water/detergent solution at an angle.
SLOWLY pour 15 ml of COLD alcohol down the side so that
it forms a layer on top of the water/wheat germ/detergent solution.
Do not mix the two layers together. (DNA precipitates at
The water-alcohol interface (the boundary between the water and the alcohol). Therefore, it is
crucial to pour the alcohol very slowly so that it forms a layer on top of the water solution. If the
alcohol mixes with the water, it will become too dilute and the DNA will not precipitate.)
7. Let the beaker sit for a few minutes. White, stringy, filmy DNA will begin to appear where the water
and alcohol meet. You will usually see DNA precipitating from the solution at the water-alcohol
interface as soon as you pour in the alcohol. If you let the preparation sit for 15 minutes or so, the
DNA will float to the top of the alcohol.
8. You can usually get more DNA to precipitate from the solution by using one of the DNA-collecting
tools (paper clip hook) OR spaghetti to gently lift the water solution up into the alcohol. This allows
more DNA to come in contact with the alcohol and precipitate. Then use paper clip hook or a
wooden stick or spaghetti to collect the DNA.
9. Place DNA on paper towel and air dry. FEEL IT. 0R
10. If time permits, place a small sample of DNA on a slide with coverslip; look at it with microscope.
Be sure to share results with all lab partners!!!
Teacher Signature: CLEAN UP !!!!!
DNA EXTRACTION
Name________________ Table#_____
Group Names: ______________________
______________________
Date________________ Per._____
______________________
______________________
50% of your Grade
is the DNA Product
Teach
sign
READ NOTES ON BACK
1. List three things available to you that you might use for a DNA source besides wheat germ, onion,
cheek cells or split peas.
2. List three things that would not be a DNA source.
3. What is the role/purpose of DNA in a cell?
4. a. Explain how DNA is contained in a cell.
b. Why does DNA extraction need to be performed in order to obtain DNA?
5. a. Describe what you saw happening in the beaker.
b. Describe the product that was obtained.
6. What is an Enzyme?
7. Why did you use detergent in the procedure, and how does it work? (see notes on back)
8. What possible benefits might be obtained by the ability to isolate the DNA of any organism?
9. Which “ingredient” (besides wheat germ,cheek cells, onions, or peas) do you think might have the most
effect on the amount of DNA you extract? __________________________________________
10. How can you test your Hypothesis? Describe an experiment to test your hypothesis.
HOW DOES IT WORK?
DNA is present in all living things from bacteria to plants to animals. In
animals, it is found in almost all cell types: cheek, muscles, reproductive cells, hair roots, -- anything
with a nucleus. DNA is NOT found in Red blood cells because they lack nuclei. White blood cells do
have a nucleus. DNA in a cell is about 100,000 times as long as the cell itself. However, DNA only
takes up about 10% of the cell's volume. How can this be? This is because the DNA molecules fold
themselves many times to pack themselves in the cell's nucleus.
Each chromosome contains a single immense molecule of DNA that, in humans, has a length of up to
12 centimeters when stretched out! (look at 12 cm on ruler) As a matter of fact, all the DNA in one
human cell (on all 46 chromosomes) is about two meters long, yet fits into a cell nucleus which is 2-3
micrometers (that's .000002 meters wide!). Yet, the DNA must still be in such a state as to allow for
enzymes to replicate the molecule or initiate the production of a protein. The 23 pairs of human
chromosomes are estimated to include about 100,000 genes.
WHEAT GERM
Wheat germ comes from wheat seeds. The “germ”
is the embryo, which is the part of the seed that can
grow into a new wheat plant. When wheat seeds are
milled into white flour, the wheat germ and wheat bran
are removed, leaving only starch. Wheat germ
contains many nutrients while wheat bran consists of
fiber. Whole-wheat flour contains all parts of the
wheat seed and is therefore more nutritious than white flour while also providing
important fiber for digestion.
CHEEK CELLS
Cheek cells come from the inner lining of mouth or the check.
These cells are routinely shed and replaced by new cells.
As the old cells die, they accumulate in the saliva in the
mouth and can easily be collected by using mouthwash.
One might say “Spit Happens”.
ONION CELLS
An onion is used because it has a low starch content, which allows DNA to be seen.
The walls of onion cells are made of cellulose, which is a polysaccharide made of
glucose. Cellulose provides a tough barrier that protects
the cell. In order to examine the contents of a plant cell,
blending helps to burst open the cell's walls and release
contents. Onion cells also have membranes that envelop
their contents. Cell membranes are made of a double
layerof lipids that allow the movement and transfer of certain
ions and substances in and out of the cell. Breaking down a
cell's membrane allows you examine the contents of the cell.
Detergents contain chemical compounds that can break down cell membranes.
Water temperature
The heat softens the phospholipids (fats) in the membranes that surround the cell and the nucleus.
It also inactivates (denatures) the deoxyribonuclease enzymes (Dnase) which, if present, would cut
the DNA into such small fragments that it would not be visible. Denatured enzymes and DNA
unravel, loose their shape, and thus become inactive. Enzymes denature at 60°C and DNA
denatures at 80°C.
Detergent
Detergent contains sodium laurel sulfate, which cleans dishes by removing fats and proteins. It
acts the same way in the DNA extraction, pulling apart the fats (lipids) and proteins that make up the
membranes surrounding the cell and the nucleus. Once these membranes are broken apart, the
DNA is released from the cell.
Soap molecules and grease molecules are made of two parts:
Hydrophilic heads: which LIKE water and Hydrophobic tails which HATE water
Both soap and grease molecules organize themselves in bubbles (spheres) with heads outside to
face the water and tails inside to hide from the water.
When soap comes close to grease, it captures it,
forming a greasy soapy ball:
A cell’s membrane has two layers of lipid (fat) molecules with proteins between them:
When detergent comes close to cell, it captures the lipids & proteins & releases DNA:
Alcohol
The DNA released from the cell nucleus is dissolved in the water/detergent/wheat germ solution and
cannot be seen. DNA precipitates out of solution in alcohol, where it can be seen. Besides allowing
us to see the DNA, the alcohol separates the DNA from the other cell components, which are left
behind in the water solution. The alcohol also causes gases dissolved in the water to be released,
which may be observed as small bubbles.
Meat Tenderizer : acts as an enzyme to cut proteins just like a
pair of scissors. The DNA in the nucleus of the cell is molded, folded,
and protected by proteins. So, the enzyme (papain) cuts the proteins
away from the DNA. Papain also helps break down DNAase, an enzyme
that breaks down DNA)
(Not used in all of the DNA extractions)
Results Questions:
1. What does the salt do?
2. What does the blender do?
3. When you mix the blended cell source with the soap, what is happening?
4. What does the alcohol do? Why does the DNA rise to the top after adding alcohol?
5. If you try a seed food such as peas, there will be more protein residue in the liquid. Why?
6. Why can’t you see the double helix
7. What part of the cell did the DNA come from?
BONUS:
1. If you did the experiment with both plant and animal cells, how would their DNA compare?