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3. Why add salt? What is its purpose?Salty water helps the DNA precipitate (solidify and appear) when alcohol is added.4. Why is cold water better than warm water for extracting DNA?Cold water helps keep the DNA intact during the extraction process. How? 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.5. How is the cell wall of plant cells broken down? It is broken down by the motion and physical force of the blender.6. What enzyme is found in meat tenderizer?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).7. 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!8. Why does the DNA clump together?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 you lined up those DNA molecules end to end, a single cell would contain six feet of DNA! If the human body is made of about 100 trillion cells, each of which contains six feet of DNA, our bodies contain more than a billion miles of DNA!9. How can we confirm the white, stringy stuff is 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.10. Isn't the white, stringy stuff actually a mix of DNA and RNA?That's exactly right! The procedure for DNA extraction is really a procedure for nucleic acid extraction.11. How long will my DNA last? Will it eventually degrade and disappear?Your DNA may last for years if you store it in alcohol in a tightly-sealed container. If it is shaken, the DNA strands will break into smaller pieces, making the DNA harder to see. 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.
The DNA molecule is structurally the same in all living things, including plants and animals. That being said, the product obtained from this extraction protocol may look slightly different depending on whether it was extracted from a plant or an animal. For example, you may have more contaminants (proteins, carbohydrates) causing the DNA to appear less string-like, or the amount of DNA that precipitates may vary.
Now that you've successfully extracted DNA from one source, you're ready to experiment further. Try these ideas or some of your own:Experiment with other DNA sources. Which source gives you the most DNA? How can you compare them?Experiment with different soaps and detergents. Do powdered soaps work as well as liquid detergents? How about shampoo or body scrub?Experiment with leaving out or changing steps. We've told you that you need each step, but is this true? Find out for yourself. Try leaving out a step or changing how much of each ingredient you use.Do only living organisms contain DNA? Try extracting DNA from things that you think might not have DNA.Want to conduct more DNA extraction experiments? Try out different soaps and detergents. Do powdered soaps work as well as liquid detergents?Frequently Asked QuestionsDownload a PDF version of this page
12. Does chromosome number noticeably affect the mass of DNA you'll see?Cells with more chromosomes contain relatively more DNA, but the difference will not likely be noticeable to the eye. The amount of DNA you will see depends more on the ratio of DNA to cell volume.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!13. Why are peas used in this experiment? Are they the best source 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.14. 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. That being said, the product obtained from this extraction protocol may look slightly different depending on whether it was extracted from a plant or an animal. For example, you may have more contaminants (proteins, carbohydrates) causing the DNA to appear less string-like, or the amount of DNA that precipitates may vary.15. What sources might I use to extract DNA from animal cells?Good sources for animal cells include chicken liver, calf thymus, meats and eggs (from chicken or fish).16. Why do peas require meat tenderizer, but wheat germ does not?We at the GSLC have done a fair amount of testing with the split pea protocol and the wheat germ protocol. We have found no difference in the "product" (nucleic acids) that is observable, whether using meat tenderizer or not. So, the step was left out of the wheat germ protocol, but kept in the split pea protocol just for fun.Even though it's not necessary, it may be doing something we can't see. For example, perhaps by using the meat tenderizer you get a purer sample of DNA, with less protein contaminating the sample.