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DNA Extraction from Wheat Germ Lab
I.
Background Information
Read the following Background Information before you start the lab experiment.
Wheat germ is the DNA source in this lab. 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 (ground up) into white flour, the wheat germ and wheat bran are removed, leaving only
starch (carbohydrate). 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.
Water temperature
The heat softens the phospholipids (fats) in the membranes that surround the cell and the nucleus.
It also denatures (inactivates) the deoxyribonuclease enzymes called DNase which is a protein. If
present, the DNase would cut the DNA into such small fragments that it would not be visible.
Denatured enzymes and DNA unravel, lose their shape, and thus become inactive. Enzymes
won’t work at 60° Celsius (140°F), and DNA denatures at 80° Celsius (176°F).
Detergent/Soap
Detergent contains sodium laurel sulfate, which cleans dishes by removing fats and proteins. It
acts the same way in the DNA extraction lab, pulling apart the fats (lipids) and proteins that make
up the membranes surrounding the cell and nucleus. Once these membranes are broken apart, the
DNA is released from the cell, then we can extract it!
Soap molecules and grease molecules are made of two parts:
 Heads, which like water
 Tails, which hate water.
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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 membranes have two layers of lipid (fat) molecules with proteins going through them.
When detergent comes close to the cell, it captures the lipids and proteins and releases the 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.
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II.
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Purpose:
The purpose of this lab is to extract DNA from wheat germ.
III.
Hypothesis:
If you add wheat germ, water, soap, and alcohol, then the DNA should appear.
IV.
Materials:
1 gram raw wheat germ
50 ml test tube
20 ml hot (50-60 °C) tap water
¼ teaspoon detergent/soap
Paper towel
14 ml 91% alcohol
V.
Procedure
1.
2.
3.
Place 1 gram of raw wheat germ in a 50 ml test tube.
Add 20 ml of hot (50-60 °C) tap water and mix constantly for 3 minutes.
Add a dropper full of detergent and mix gently every minute for 5 minutes. Try not to
create foam.
4. Use a piece of paper towel to remove any foam from the top of the solution.
5. Tilt the test tube at an angle. SLOWLY pour 14 ml of 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).
6. Let the test tube sit for a few minutes. White, stringy, filmy DNA will begin to appear
where the water and alcohol meet. Observe the DNA inside the test tube.
VI.
Results – ANSWER AFTER THE LAB
1. What was the purpose of using warm water in this experiment?
2. What was the purpose of using alcohol in this experiment?
3. Describe the physical appearance of your extracted DNA (what it looked like).
4. What are some possible errors in this experiment? (For example: could your
group have measured the wrong amount of something? Not poured the alcohol
slowly enough? Not mixed constantly enough for the right amount of time)
5. What did you learn from this experiment?
VII. Conclusion
This is where you summarize your experiment. Restate your purpose and hypothesis.
Summarize your materials and the procedure (in detail). Rewrite the results (questions).
You must write the entire question and a thorough/thoughtful answer. One word answers
will not be accepted.