18 Experiment 12: Isolation of DNA
CHEM 1014 DNA experiment
Everyone has a unique set of fingerprints, which is why fingerprinting is so useful for identifying people. For nearly 100 years, fingerprints have been used to track criminals. They also have been used to identify murder victims and soldiers killed in combat. Fingerprints aren’t always helpful in catching criminals, however. People who commit crimes often remember to wear gloves or at least to wipe away their prints. Even when police find a print, they can only compare it to the ones they have on file. If the culprit has never been arrested before, police won’t find a match. Using fingerprints isn’t always useful for identifying bodies, either. Prints can’t be taken from a badly damaged corpse such as one burned in a fire, torn apart by a bomb, or decayed. Even when you can get good prints, you need something to match them to. Unless you have an idea of who the person might be, and that person’s prints are in records somewhere, the fingerprints from the body aren’t of any use. This is why there is so much excitement about DNA fingerprinting, or DNA typing, as it is also called. In many ways, DNA typing is a much better identification tool than prints from fingers. The actual process involved in DNA typing is quite complicated. What it does, however, is rather simple: It turns each DNA sample into a set of lines, like the bar code you find on the price tags for store products. The lines of one DNA sample can be compared to the lines of another sample to see if they are alike.
A sure match between two samples can be made only if entire DNA sequences are compared. That’s such a huge task that it’s not yet possible. So what DNA technicians do instead is compare several sections of DNA. If all the tested sections match, technicians can use mathematical formulas to estimate the odds that both samples come from the same person. DNA testing cannot absolutely prove a match, but it can come very close. One of the great advantages of DNAtyping is that there are so many ways to get a “print.” You can use hair, blood, saliva, semen, skin, and nail clippings, because they all are made up of cells containing DNA. For identifying bodies, DNA typing is better than fingerprinting because DNA lasts longer. After someone dies, the flesh decays quickly. This makes it difficult to get fingerprints. However, bones, teeth, and hair last a long time, and DNA typing using these materials can be done long after death. DNA can also be analyzed for special information that fingerprints don’t give. For example, DNA can be used to tell whether two people come from the same family. DNAcan also be examined for important clues about persons, such as their gender and other physical characteristics. This might be done if, for example, some bones are found, and you want to figure out whom they belong to. Uses for DNA Typing DNA typing was first introduced in the early 1980s. Here are some of the ways it has been used since then:
▼ To prove innocence. DNA typing has been submitted as evidence in thousands of cases in the U.S. and other countries. In about onethird of these cases, it has been used to prove people innocent by showing that their DNA does not match the sample found at the crime scene. It also has been used to prove the innocence of people behind bars, including some death row inmates. For these inmates, DNA typing did not exist or was still too new when they were first tried. DNAevidence can last for years, for example, in semen stains on clothing. Lawyers have used this evidence at retrials to show that their client could not be the guiltyparty because his or her DNA type does not match the evidence.
▼ To prove guilt. It is harder to use DNA as evidence to convict a person because juries need to find the defendant guilty “beyond a reasonable doubt.” DNA typing by itself leaves some doubt because there is always the chance that someone else besides the accused has matching DNA for the sections that were tested. There also is the chance that someone “planted” the DNA to pin the crime on the accused or that the testing lab has made a mistake. However, testing labs have improved their procedures to reduce the risk of false matches. Lawyers have learned how to combine DNA typing with other evidence to strengthen their case. For these reasons, prosecutors are becoming more successful at using DNA to pin the accused to the scene of a crime. ▼ To identify relatives. Children of foreign-born residents of the U.S. and many other countries are allowed by law to enter and live here. Immigration officers have sometimes tried to block the entry of people they suspected were not really the children of legal residents. DNA typing has been used to prove a family relationship and allow legal entry. ▼ To prove fatherhood. DNA typing has been used to prove or disprove paternity, that is, whether a man is the father of a child. It has been used in cases where the woman is suing for child support from a man who denies that he is the father. It also has been used in cases where a man wants to share custody of a child but the woman denies that he is the father. ▼ To identify bodies. DNA typing has helped identify numerous murder and accident victims. For example, DNA typing was used to identify one of the victims of the 1995 bombing of the federal building in Oklahoma City. Long after all the bodies of the known victims were recovered, a leg was found in the rubble. DNAtesting concluded that it belonged to an African-American woman. They used this clue to help identify her. ▼ To identify soldiers. The U.S. military used to rely on dog tags to identify the remains of soldiers. Now it uses DNA typing. Blood and saliva samples are taken from new recruits and stored. If that soldier dies in combat and the body is too damaged to identify, DNA from the body can be compared to the DNA in the stored samples. DNA typing was first used to identify soldiers killed in the Persian Gulf War.
▼ To uncover history. Examining the DNA of people long dead has been used to reveal information about the past. For example, DNA testing was used to identify the bodies of Czar Nicholas II and his family. This royal family was murdered at the beginning of the Russian Revolution in 1917, and the bodies were never found. In 1995, researchers used DNA typing to confirm that the bodies in a mass grave belonged to members of the Czar’s family. ▼ To study human evolution. Scientists are collecting DNA samples from people worldwide. They also are collecting DNA from the preserved skeletons of humans who lived thousands of years ago. They are using this information to better understand how the first humans on earth evolved into the many different peoples of the world.
Issues of Privacy Computers are part of what makes DNA typing such a powerful tool. They can store information from millions of DNA samples. Plus, they can rapidly search through all of this information to find matches. It is this power that concerns Donita, the woman who doesn’t know if she should take part in the DNA screening. If Donita cooperates, her DNAprint will go into the police’s data bank, along with prints from all the other factory workers. The prints will be compared to the DNA from the hairs found in the victim’s hand. Unless those hairs came from Donita’s head, her DNA sample should remove her as a suspect. But her DNA sample may not be removed from the police computer. It may become part of a permanent file. This means that every time the police search their computer to find a match for some DNA evidence found at some crime scene, they will be checking her DNA print. In essence, she will be a permanent suspect. From Donita’s point of view, this is a permanent invasion of privacy. “Privacy” has many definitions. One definition is “the right to be left alone.” As long as her print is on file, Donita is not being left alone. She may never be approached by the police again, but they will always be “looking” at her.
Another definition of “privacy” is “the right to decide for yourself what information others can know about you.” By giving police her DNA, Donita will be releasing all sorts of information about herself. There is the possibility that they will not only type her DNA, but also test it to learn many things about her. The effect on Donita may be a feeling of loss of control over personal information. Another concern for Donita is whether the police will keep the DNA information they have on her secret from others. How will the police safeguard these files? Will they permit the use of the files for purposes that don’t have to do with law enforcement? Finally, if privacy is the right to decide what information others can learn about you, it also is the right to decide what information you learn about yourself. If Donita’s DNA sample is typed, she may learn some things by accident that she never expected to find out. Perhaps she will learn that she is the carrier of a gene mutation that could lead to disease. Perhaps she will learn that she doesn’t share certain genetic traits with her parents and therefore must be adopted. There is all sorts of information that DNA can reveal that people may not want to find out. Controls on DNA Files Mass DNA screenings like the one at Donita’s factory have been used by police in several regions of the world, including England, Wales, and Germany. A new law in England allows the police to take hair or saliva samples from suspects for DNA typing, even without permission. England also has created the world’s first nationwide DNA computer data bank. Mass DNA screening to solve crimes has not yet happened in the U.S. This country has a strong tradition of protecting privacy. The Fourth Amendment to the Constitution protects citizens against “unreasonable search and seizure.” In Donita’s case, there is no reason to suspect her of the murder, except that she worked at the factory where it took place. Therefore, taking her DNA might be ruled an “unreasonable search” by a U.S. court. Also, even though she is being asked to volunteer a blood sample, the courts may feel that this is an “unreasonable seizure” because she is being pressured to give a sample.
However, we don’t know for certain how U.S. courts would rule. There hasn’t been a court case around this issue yet, so we just don’t know. It’s possible that someday mass DNA screenings could become a common tool of U.S. police. Even without mass DNA screenings, however, U.S. law enforcement DNA data banks are growing. Many states require convicted felons and sex offenders to give blood or saliva samples for DNA typing as a condition for parole. The idea is for police to be able to use these data banks to catch repeat offenders. The FBI also is building a DNA data bank of criminals. It is possible that DNA samples may someday be taken from people who are convicted of misdemeanors. This means that even if you get stopped for speeding, your DNA could end up in police files. It is also possible that information from your DNA could end up in other types of data banks. Today, there are many instances where you have to release personal and medical information about yourself. This happens when you apply for a job, for life or health insurance, for credit, for financial aid, or for benefits from the government. If the results of any DNA tests become part of your records, you may have to release the information in order to obtain needed services. Right now, there are no laws concerning DNA data banks. There is no law which says that a blood sample collected for one kind of DNA testing can’t be used for another purpose. There is no law that limits data bank employees from snooping in your files. There is no law that gives you the right to check your DNA file to find out what information is there or to make sure the information is correct. Some people say that we need to come up with rules for how DNA data banks operate. They say it would be easier to set up the rules now, before the practice of storing and sharing DNA information in computers grows any larger. But technology often moves faster than lawmaking. People may not demand this privacy protection until after they have had their DNA on file somewhere. Our growing ability to gather DNA information is making many changes in our ways of life. However, it is not just we humans who are affected. The world is also changing for other animals and for plants as well. We look at these changes in our next chapter.
Source: https://www.aaas.org/sites/default/files/yourgenes.pdf
Baker, Catherine. Your Genes, Your Choices: Exploring the Issues Raised by Genetic Research. Washington, D.C.: AAAS, 1999. Describes the Human Genome Project, the science behind it, and the ethical, legal, and social issues raised by the project.
Objective
1. If possible, before doing this activity, make and show a slide of some cheek cells and stain it with methylene blue so that students can see the shape of the nucleus of the cheek cell. 2. Provide each student with a copy of the “See Your DNA” student handout and a set of materials. Before students begin, make sure they understand and will follow guidelines for maintaining sterile conditions. 3. Have students prepare their saltwater and detergent solutions. When they are done, have each student swill two teaspoons of the saltwater solution in their mouths for 30 seconds. Make sure that students swish the solution around for the full 30 seconds. This will remove dead cells lining the mouth and provide students with a source of their own DNA. 4. Have students spit their solution into a disposable plastic cup and then pour it into a large test tube containing 1 teaspoon (5ml) of the detergent solution. 5. Students should cap the test tube and gently rock it on its side for 2-3 minutes. It is important that students are not too vigorous while mixing. DNA is an extremely long molecule. Physical abuse can break it into smaller fragments, a process known as shearing. 6. After gently rocking the solution, have students uncap the tube and then slightly tilt it and carefully pour 1 teaspoon (5ml) of the chilled ethanol down the inside of the tube so that it forms a layer on the top. Again, it is very important that the students take care in adding the ethanol so that the alcohol floats above the soapy solution already in the tube. 7. Tell students to allow the tube to stand for one minute. Then, have them use a thin acrylic or glass rod to slowly move some of the ethanol into the soap layer. The alcohol/soap interface is where most of the DNA will precipitate out of the soap solution. Have students twirl the rod to spool the DNA strands around it. If too much shearing has occurred, the DNA fragments may be too short to wind up, and they may form clumps instead. Students can try to scrape these out. 8. After students have wrapped as much DNA on the rod as they can, have them remove the rod and scrape or shake the DNA into a small tube with the remaining ethanol. Tell students that the DNA in their test tubes came from the nucleus of their cells, specifically, the 46 chromosomes in the nucleus. 9. Now that students have their DNA, what will they do with it? Will they grant consent for its use or keep it private from everyone? How will they guarantee this? Work with students to draft a policy statement concerning their own DNA. Use of Ethanol
DNA is only about 50 trillionths of an inch long. The reason it can be seen in this activity is because students are releasing DNA from a number of cells. This happens when the detergent or dishwashing liquid breaks, or lyses, the membranes around the cell and around the nucleus. Once released, the DNA from the broken open cells intertwines with DNA released from other cells. Eventually, enough DNA intertwines to become visible to the eye as whitish strands. Tell students that one strand of DNA is so thin (.0000002mm) they would never be able to see it without using a microscope. Detergents break open cells by destroying the fatty membrane that encloses them. This releases the cell contents, including DNA, into the solution. Detergents also help strip away proteins that may be associated with the DNA. DNA is not soluble at high ethanol concentrations, so it precipitates out as long strands. Salts, such as sodium chloride, also greatly aid in precipitating DNA. The ethanol also causes gases dissolved in the water to be released, which may be observed as small bubbles. This procedure may not work well if the researcher has eaten corn flakes for breakfast. Presumably this is because the corn flakes have scoured too many buccal cells from the inside of the mouth. Repeating may give low yields if most of the loose buccal cells have already been harvested. Source: https://www.pbs.org/wgbh/nova/teachers/activities/2809_genome.html
Good graphics here: https://www.ox.ac.uk/sites/files/oxford/field/field_document/Biochemistry%20workshop%20presentation.pdf http://www.planet-science.com/categories/experiments/biology/2012/03/extract-your-own-dna.aspx
Can DNA be found in human eukaryotic cells? DNA, a polar molecule composed of two complementary chains of nucleotides wound in a double helix, is present in all living things from bacteria to plants to animals. In animals, it is found in almost all cell types: muscle fibers, reproductive cells, white blood cells, and skin cells; red blood cells do not contain a nucleus thus no nucleic DNA. The basic procedure for extracting DNA is the same, regardless of its source, although the specifics may vary:
Extracting DNA is a moderately simple process. The activity begins by collecting cheek cells by rinsing the mouth with purified drinking water and gently scraping the oral cavity with the teeth. This process will help gather numerous epithelial cells lining the oral cavity. A soap is then added to the cheek cell solution in order to split or break the cells open. This process releases the DNA from inside the cells and nuclei because the amphiphilic properties of the detergent break apart the fatty and protein components that make up cellular and nuclear membranes. A concentrated saline solution is then added to the cheek cell solution in order to change the polarity of the solution. This process will allow DNA, a polar or slightly negatively charged molecule by nature when released from nuclei, to dissolve in the ionic solution while many fats, carbohydrates and proteins settle out. Having a polarity is a major characteristic that allows the DNA to separate from the solution. Finally, the DNA is then precipitated from the ionic solution by the adding 70-90%+ isopropyl alcohol. This process will allow DNA, which is not soluble in the alcohol, and the alcohol, which are both less dense than the ionic solution, to appear towards the top of the solution. The density of DNA is also a characteristic of allowing it to separate from solution. The DNA will appear white and cloudy and/or thread-like during the precipitating period. The hypothesis for the procedure is that a collection of DNA can be extracted from human epithelial cells, isolated and observed. Method
Apparati:
Class:
Salt (Must be non-ionized “Canning Salt”) Liquid soap (ie Dawn) 70% + Isopropyl alcohol “cooled” ; 100 mL beaker to contain Distilled water Drinking or tap water Electronic balance (with filter paper or weighing boat) Methylene blue (optional)
Group: Note: All items list below should be sterile and properly clean before using for each step:
Procedure: Note: Soap and saline solutions are to be used for both partners..
Optional: Add a few drops of “methane blue stain”. The stain will target DNA by bonding to the molecule due to its positive, flat, ringed characteristics.
References
How to extract DNA from any living thing. Retrieved from http://www.lewport.wnyric.org/jwanamaker/download/easy_dna_extraction.pdf
Using genetic evidence to evaluate group behavior. Retrieved from http://biology.arizona.edu/sciconn/ lessons2/Vuturo/vuturo/dna.htm
|
|||||||||||
Lab: DNA Extraction from Human Cheek Cells
Introduction
DNA…you hear about it all the time. DNA is used every day by scientists and lawyers to help in criminal investigation, paternity suits, cloning, etc. Your DNA is your “genetic fingerprint”—this means that your DNA is like no one else’s in the world! The procedure that we will use to see your DNA includes the same basic processes that researchers use to isolate, analyze, and manipulate DNA in a laboratory setting (although the DNA isolated here is not nearly as “pure” as the research lab version).
DNA is a nucleic acid, made of carbon, hydrogen, oxygen, nitrogen, and phosphorous. DNA can be considered the hereditary “code of life” because it possesses the information that determines an organism’s characteristic and is transmitted from one generation to the next. You receive half of your genes from your mother and half from your father. Day to day, DNA’s job is to direct the functioning within the cells of your body.
DNA is in the nucleus of almost every cell in your body. The length of DNA per cell is about 100,000 times as long as the cell itself. However, DNA only takes up about 10% of the cell’s volume. This is because DNA is specially packaged through a series of events to fit easily in the cell’s nucleus. The structure of DNA, the double helix, is wrapped around proteins, folded back onto itself, and coiled into a compact chromosome.
Individual chromosomes can be studied using microscopes, but the double helix of a chromosome is so thin that it only be detected through innovative, high-tech procedures. Chromosomal DNA from a single cell is not visible to the naked eye. However, when chromosomal DNA is extracted from multiple cells, the amassed quantity can easily be seen and looks like strands of mucous-like, translucent cotton.
We will first collect cheek cells by swishing water in our mouths and using our teeth to scrape cells off our cheeks. (The more vigorous and the longer that you swish, the more cells are removed, and the more materials you’ll have from which to extract DNA.) Then, we will lyse the cell membranes by adding a detergent based cell lysis solution, which allows the DNA to be freed. DNA is soluble in water, but much less soluble in alcohol. Thus, alcohol will be slowly added, and DNA will precipitate to the water/alcohol interface, and you will be able to see your own DNA! The white, stringy material is thousands of DNA molecules stuck together (with some proteins too).
Materials and Methods
- Label your 15mL test tube with a piece of tape and your initials.
- Obtain a small cup of water and swish it around in your mouth for 1 full minute. As you swish, gently and continuously scrape the sides of your cheeks with your teeth to help release your cheek cells.
- Spit the water (with your collected cheek cells) back into the small cup.
- Pour the contents of the cup into your labeled test tube (discard the cup).
- Holding the test tube at an angle, use the provided plastic pipet to add a pipette full of cell lysis solution to your collected cheek cells.
- Cap your test tube, and invert it 5-8 times. (This mixes the lysis solution with the cheek cells.)
- Allow this to stand for 2 minutes.
- Using the provided pipet, add the cold alcohol by letting it run gently run down the side of the test tube (hold the test tube at an angle). Add the alcohol until your total volume reaches 12-13mL. You should have 2 distinct layers. DO NOT mix the cheek cell solution with the alcohol!!!
- Watch as wispy strands of translucent DNA begin to clump together where the alcohol layer meets the cheek cell solution. (It kind of looks like cobwebs extending upward.)
- Place your 15mL test tube in a test tube rack and let it stand undisturbed for 15 minutes. During this time the DNA will continue to precipitate out.
- Use a plastic pipette to transfer your DNA into a smaller test tube. To do so, place the pipet near the DNA and draw the DNA into the pipet (along with some alcohol). Do not move your pipet up and down into the bottom layer.
Discussion Questions
- What are the 5 elements that make up DNA? ____________________________________________________________________________________________________________
- What is the function of DNA from day to day? ______________________________________________________
- Describe how long strands of double-helical DNA fit into the nucleus of a single cheek cell. ______________________________________________________
- What was the purpose of using the cell lysis solution? ______________________________________________________
- Why does the DNA become visible once the alcohol is added? ______________________________________________________
- If DNA is so thin, how is it that we are able to see it during this simple lab exercise? ______________________________________________________
- Why is DNA referred to as your genetic fingerprint? ______________________________________________________
- Give some examples of how DNA is used everyday. __________________________________________________________________________________________________________________________________________________________________
TEACHERS’ NOTES In order to understand what you are doing in this activity, it isimportant that you know the “big picture” behind the methods we will beusing: · Cells may be physically and chemically treated to break open the outer cell membrane and inner nuclear membrane. · The portion of the cell mixture containing DNA (the watery portion) will be separated from the cell membranes and organelles (the gloppy portion). · The solution containing dissolved DNA will be chemically altered so that the DNA can precipitate out of the solution in its solid, string-like state.
Additional Notes· The recipe for the Salt/detergent mixture is: 2 L distilled water, 100 mL detergent (we use Palmolive dishwashing detergent), 15 g salt. · The ethanol needs to be ice cold–keep in freezer until the time it is needed. · There is about a 15-minute wait time–plan something DNAish during this time.
STRAWBERRIES:
DNA Isolation from Strawberries Developed by Diane Sweeney http://www.caseciw.org/first_light_case/horn/strawberries/strawbdnaproc.html Teacher Background This is a simple, effective protocol for spooling DNA. Ripe strawberries are an excellent source for extracting DNA because they are easy to pulverize and contain enzymes called pectinases and cellulases that help to break down cell walls. And most important, strawberries have eight copies of each chromosome (they are octoploid), so there is a lot of DNA to isolate. The purpose of each ingredient in the procedure is as follows: Shampoo or dishwasher soap helps to dissolve the cell membrane, which is a lipid bilayer. Sodium chloride helps to remove proteins that are bound to the DNA. It also helps to keep the proteins dissolved in the aqueous layer so they don’t precipitate in the alcohol along with the DNA. Ethanol or isopropyl alcohol causes the DNA to precipitate. When DNA comes out of solution it tends to clump together, which makes it visible. The long strands of DNA will wrap around the stirrer or transfer pipet when it is swirled at the interface between the two layers. Notes on Materials and Recipes • Use Ziploc TM freezer bags rather than sandwich bags, as they are thicker. • Fresh or frozen strawberries can be used. Be sure to thaw the frozen berries at room temperature. Bananas or kiwi fruit can also be used but yield less DNA. • Use non-iodized table salt or laboratory-grade sodium chloride. • 95% ethanol or 91 or 100% isopropyl alcohol can be used to precipitate the DNA. Isopropyl alcohol can be purchased from a pharmacy. Whichever you use, make sure it is ice cold by placing in an ice-water bath or in the freezer. DNA Extraction Buffer • 100 ml (3/8 cup) shampoo (without conditioner) or 50 ml dishwasher detergent • 15 grams sodium chloride (2 teaspoons) • water to 1 liter The GENETICS Project Department of Genome Sciences University of Washington http://chroma.mbt.washington.edu/outreach/genetics 2 DNA Isolation from Strawberries Student Directions Materials per student group • 1-3 strawberries (about the volume of a golf ball). Frozen strawberries should be thawed at room temperature. • 10 ml DNA Extraction Buffer (soapy salty water) • about 20 ml ice cold 91% or 100% isopropyl alcohol • 1 Ziploc TM bag • 1 clear test tube • 1 funnel lined with a moistened paper towel • 1 coffee stirrer or transfer pipet Directions 1. Remove the green sepals from the strawberries. 2. Place strawberries into a Ziploc TM bag and seal shut. 3. Squish for a few minutes to completely squash the fruit. 4. Add 10 ml DNA Extraction Buffer (soapy salty water) and squish for a few more minutes. Try not to make a lot of soap bubbles. 5. Filter through a moistened paper towel set in a funnel, and collect the liquid in a clear tube. Do not squeeze the paper towel. Collect about 3 ml liquid. 6. Add 2 volumes ice cold isopropyl alcohol to the strawberry liquid in the tube. Pour the isopropyl alcohol carefully down the side of the tube so that it forms a separate layer on top of the strawberry liquid. 7. Watch for about a minute. What do you see? You should see a white fluffy cloud at the interface between the two liquids. That’s DNA! 8. Spin and stir the coffee stirrer or transfer pipet in the tangle of DNA, wrapping the DNA around the stirrer. 9. Pull out the stirrer and transfer the DNA to a piece of saran wrap or clean tube. The fibers are thousands and millions of DNA strands. 10. To view in a microscope, put the glob on a clean slide and gently tease/stretch apart using 2 toothpicks or dissecting pins. The fibers will be easier to see in the teased-apart area. 11. Rinse your funnel. Put the Ziploc TM bag and paper towel in the garbage.
https://www.gs.washington.edu/outreach/dhillon_dnaprocedure.pdf
https://imb.uq.edu.au/files/32865/Strawberry%20DNA%20Extraction.pdf
https://imb.uq.edu.au/strawberry-dna-extraction-activity
All living things have DNA: the chemical instructions on how to make a living thing, from humans to strawberries.
Many people assume that because DNA is so small, we can’t see it without powerful microscopes. But in fact, DNA can be easily seen with the naked eye when collected from thousands of cells.
Have a go at completing this fun research activity to extract and view DNA from a delicious strawberry.
And once you have completed it, be sure to share a photo of your successful experiment with us on social media by tagging us on Twitter and Facebook.
DNA: background information
What does DNA stand for?
DNA stands for deoxyribonucleic acid.
DNA is a long molecule in the shape of a double helix – two spirals twisting around each other. These spirals are the backbone of the DNA, and are made up of sugars and phosphates. The spirals are connected by chemicals known as bases, which stretch between the spirals like the rungs of a ladder. DNA has four types of bases: adenine (A), thymine (T), guanine (G) and cytosine (C). A and T always join together, as do G and C.
What does DNA do?
Our genes are made up of DNA, and DNA contains our unique genetic code.
Like a recipe book or instructions for lego , DNA holds the instructions for making all our proteins, which do all the jobs in our bodies.
Genes in common
You don’t look much like a fly or a worm. But, believe it or not, you share genes with both of them and with every other living thing. Scientists study the genes in bacteria, zebrafish and other living things to learn more about humans.
How much DNA do you share with these living things?
Why do we use the dishwashing liquid?
The dishwashing liquid bursts open the cells of the strawberries, releasing the DNA.
Why do we use the salt?
It ensures that the proteins in the cell are kept separate from the DNA.
What does the alcohol do?
When molecules are insoluble (unable to be dissolved), they clump together and become visible. DNA is not soluble in alcohol; therefore, it makes the DNA strands clump together and become visible to the naked eye.
https://www.genome.gov/Pages/Education/Modules/StrawberryExtractionInstructions.pdf
https://www.pbs.org/wgbh/nova/teachers/activities/pdf/3214_01_nsn_01.pdf
Feedback/Errata