DNA EXTRACTION LAB
Genetic Science Learning Center
http://gscl.genetics.utah.edu/wheatgerm/
Materials Needed
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Raw wheat germ Liquid detergent - 1 ml or 1/4 teaspoonAlcohol - 14 ml or 1 tablespoon50-60ｰ Celsius tap water - 20 ml or 1 tablespoonDo not use water hotter than 50-60ｰ C. 50 ml beakers Graduated cylinder Wooden applicator stick Eyedropper
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Procedure
Weigh 1 gram of wheat germ and place in the 50ml beaker.
Add 20 ml or 1 tablespoon of hot (50-60 ｰC) tap water and mix constantly for 3 minutes.
Add 1 ml detergent and mix gently every minute for 5 minutes. Try not to create foam.
Use an eyedropper remove any foam from the top of the solution.
Tilt the test tube, beaker or jar 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). 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.
Let the test tube, beaker or jar 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.
You can usually get more DNA to precipitate from the solution by using one of the DNA-collecting tools (such as a glass or paper clip hook) to gently lift the water solution up into the alcohol. This allows more DNA to come in contact with the alcohol and precipitate. You may find it helpful to pour the water/detergent solution into a clean test tube, leaving behind the wheat germ, before adding the alcohol
What is DNA?
DNA is the abbreviation for deoxyribonucleic acid.
DNA is found in the nucleus of every cell & it stores the information that makes up living organisms
It is a double helix of 4 nucleotides. It contains a code hat allows the body to make up proteins.
The nucleotides are
CYTOSINE GUANINE
ADENINE
THYMINE
When forming the double helix the nucleotides will only bind this way
CYTOSINE-GUANINE
GUANINE-CYTOSINE
ADENINE-THYMINE
THYMINE-ADENINE
Why use 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.
What does the detergent do?
Detergent cleans dishes by removing fats. It acts the same way in the DNA extraction protocol, 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.
Soap molecules and grease molecules are made of two parts:
Heads, which like water
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.\
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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.
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When detergent comes close to the cell, it captures the lipids and proteins and releases the DNA.
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What does the alcohol?
The DNA released from the cell nucleus is dissolved in the water/detergent/wheat germ solution and cannot be seen. DNA precipitates (separates) 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
What does the warm water do?
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.
Enzymes are proteins which help chemical reactions in the body speed up.
Denatured enzymes and DNA unravel, loose their shape, and thus become inactive. Enzymes denature at 60ｰ Celsius, and DNA denatures at 80ｰ Celsius.
DNA Graphic from
library.thinkquest.org/
