The cold alcohol helps the DNA precipitate solidify and appear more quickly. Make sure that you started with enough DNA. Many food sources of DNA, such as grapes, also contain a lot of water.
If the blended cell soup is too watery, there won't be enough DNA to see. To fix this, go back to the first step and add less water. The cell soup should be opaque, meaning that you can't see through it. Cold water helps keep the DNA intact during the extraction process. Cooling slows down enzymatic reactions. This protects DNA from enzymes that can destroy it.
Why would a cell contain enzymes that destroy DNA? These enzymes are present in the cell cytoplasm not the nucleus to destroy the DNA of viruses that may enter our cells and make us sick.
A cell's DNA is usually protected from such enzymes called DNases by the nuclear membrane, but adding detergent destroys that membrane. The two most common enzymes used in meat tenderizer are Bromelain and Papain.
These two enzymes are extracted from pineapple and papaya, respectively. They are both proteases, meaning they break apart proteins. Enzymatic cleaning solutions for contact lenses also contain proteases to remove protein build-up. These proteases include Subtilisin A extracted from a bacteria and Pancreatin extracted from the pancreas gland of a hog. How much pineapple juice or contact lens solution should I use to replace the meat tenderizer?
You just need a drop or two, because a little bit of enzyme will go a long way. Enzymes are fast and powerful! DNA precipitates when in the presence of alcohol, which means it doesn't dissolve in alcohol. This causes the DNA to clump together when there is a lot of it. And, usually, cells contain a lot of it! For example, each cell in the human body contains 46 chromosomes or 46 DNA molecules.
If the human body is made of about trillion cells, each of which contains six feet of DNA, our bodies contain more than a billion miles of DNA! There is a protocol that would allow you to stain nucleic acids, but the chemical used would need to be handled by a teacher or an adult. So, for now, you'll just have to trust that the molecules precipitating in the alcohol are nucleic acids.
That's exactly right! The procedure for DNA extraction is really a procedure for nucleic acid extraction. Your DNA may last for years if you store it in alcohol in a tightly-sealed container. If it disappears it's likely because enzymes are still present that are breaking apart the DNA in your sample.
Using more sophisticated chemicals in a lab, it is possible to obtain a sample of DNA that is very pure. DNA purified in this way is actually quite stable and will remain intact for months or years. Cells with more chromosomes contain relatively more DNA, but the difference will not likely be noticeable to the eye.
For example, plant seeds yield a lot of DNA because they have very little water in the cell cytoplasm. That is, they have a small volume. So the DNA is relatively concentrated. You don't have to use very many seeds to get a lot of DNA!
Peas are a good source of DNA because they are a seed. But, we also chose the pea for historical reasons. Gregor Mendel, the father of genetics, did his first experiments with the pea plant. How does the experiment compare when using animal cells instead of plant cells? The DNA molecule is structurally the same in all living things, including plants and animals.
Let the solution drain 5 minutes. Do not agitate the solution. Let the solution sit for two minutes without disturbing it. The DNA will appear as transparent, slimy, white mucus which can be spooled up with the wood applicator stick. Why do we use shampoo? What does the salt do? Why do we need to cool the mixture? What does the cold ethanol do?
Discussion Questions To extract DNA from cells, what must you isolate it from in the case of a plant such as strawberry? What steps did we use to extract the DNA? What is DNA used for when it is extracted? After the cell walls have been disrupted during mechanical mashing of the fruit, the detergent in the shampoo disrupts the cell and nuclear membranes of each cell to release the DNA.
It does this by dissolving lipids and proteins that hold the membranes together. A single strand of DNA is extremely tiny, too tiny to see with the naked eye, but because the DNA clumped in this activity you were able to see just how much of it three strawberries have when all of their octoploid cells are combined!
This activity brought to you in partnership with Science Buddies. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Go Paperless with Digital. Be careful to pour down the side of the container to form a layer on top instead of mixing the two layers.
The peas are initially ground in the blender to remove the shells. This is like what happened to the egg in vinegar. Each pea cell is still surrounded by a cell membrane. Adding detergent does this. Just as soap is able to remove dirt from your hands, the detergent molecules surround particles in the cell membrane to remove them.
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