experiment on dna extraction

NOTIFICATIONS

Dna extraction.

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DNA extraction is a routine procedure used to isolate DNA from the nucleus of cells.

The long stringy nature of DNA is hard to conceptualise. By extracting it, the concept can become easier to understand. This activity outlines how to extract the DNA from a tomato.

What does DNA extraction involve?

Step 1. breaking cells open to release the dna.

The cells in a sample are separated from each other, often by a physical means such as grinding or vortexing , and put into a solution containing salt. The positively charged sodium ions in the salt help protect the negatively charged phosphate groups that run along the backbone of the DNA.

A detergent is then added. The detergent breaks down the lipids in the cell membrane and nuclei . DNA is released as these membranes are disrupted.

Step 2. Separating DNA from proteins and other cellular debris

To get a clean sample of DNA, it’s necessary to remove as much of the cellular debris as possible. This can be done by a variety of methods. Often a protease ( protein enzyme) is added to degrade DNA-associated proteins and other cellular proteins. Alternatively, some of the cellular debris can be removed by filtering the sample.

Step 3. Precipitating the DNA with an alcohol

Finally, ice-cold alcohol (either ethanol or isopropanol ) is carefully added to the DNA sample. DNA is soluble in water but insoluble in the presence of salt and alcohol. By gently stirring the alcohol layer with a sterile pipette, a precipitate becomes visible and can be spooled out. If there is lots of DNA, you may see a stringy, white precipitate.

Step 4. Cleaning the DNA

The DNA sample can now be further purified (cleaned). It is then resuspended in a slightly alkaline buffer and ready to use.

Step 5. Confirming the presence and quality of the DNA

For further lab work, it is important to know the concentration and quality of the DNA.

Optical density readings taken by a spectrophotometer can be used to determine the concentration and purity of DNA in a sample. Alternatively, gel electrophoresis can be used to show the presence of DNA in your sample and give an indication of its quality.

What can this DNA be used for?

Once extracted, DNA can be used for molecular analyses including PCR, electrophoresis, sequencing, fingerprinting and cloning.

Related content

In From the smallest bones come the biggest secrets read about the work of former University of Otago Masters student Lachie Scarsbrook. He developed a specialised technique that allows scientists to extract ancient DNA from tiny precious remains and sequence their genomes without damaging the original fossil.

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Practical Biology

A collection of experiments that demonstrate biological concepts and processes.

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Practical Work for Learning

Published experiments

Extracting dna from living things, class practical or demonstration.

You can extract DNA – to see what it is like – from some plant and some animal material using equipment and chemicals you might find in a kitchen. For more thorough analytical work, you need more control over the components of your chemicals, and it may be worth investing in a kit from one of the major suppliers. This is a rough and ready method that should give reasonable quantities of DNA from quite large quantities of material.

Lesson organisation

You can run this as a demonstration, or as small group work. Or you could prepare enough of each of several materials to allow groups to take samples from which they extract the DNA.

Apparatus and Chemicals

For each group of students:.

Access to water bath at 60 °C (optional)

Test tube, 1, for each sample to be used

Ice cold ethanol (IDA), 10 cm 3 for each sample to be used

Wooden spill, straw, glass rod or inoculating loop, 1 per sample

For the class – set up by technician/ teacher:

Blender for each material to be used or knives to chop material and a mortar and pestle to grind material for each working group

Ice bath to keep materials cool as necessary ( Note 1 )

Source/s of DNA ( Note 2 ) – to produce 10-20 cm 3 of blended material per sample

Table salt, a pinch (or 1 cm 3 ) for every 300 cm 3 sample ( Note 3 )

Strainer for each material to be used

Detergent, 30 cm 3 for each 300 cm 3 of blended material to be processed

Protease, for example, pineapple juice, contact lens cleaner, pinch of meat tenderiser

Health & Safety

• Take care with ethanol IDA (see CLEAPSS Hazcard) – which is highly flammable and harmful through skin contact because of the presence of methanol.
• Protease (see CLEAPSS Hazcard) is harmful as a powder and irritant in solution. Wear eye protection and wash off skin promptly.
• Electrical equipment: Any electrical appliances used in the lab should be checked according to your employer’s systems. Use a blender dedicated for laboratory activities, not one that will be used later to process food for human consumption.

Read our standard health & safety guidance

1 Using ice-cold ethanol and ice-cold water increases the yield of DNA. Low temperatures protect the DNA by slowing down the activity of enzymes that could break it apart. A cell’s DNA is usually protected from such enzymes (DNases) by the nuclear membrane which is disrupted by adding detergent. DNases in the cytoplasm would destroy the DNA of viruses entering the cell. Cold ethanol helps the DNA to precipitate more quickly. Chill the ethanol in a screwcap plastic bottle in the prep room freezer. Below 4 °C ethanol is below its flashpoint so this is safe even if your freezer is not spark proof.

2 You can use a variety of substances for this extraction. The original of this protocol recommended split peas, but onions, and fish eggs or fish sperm (milt) are commonly recommended. It is important to check that your source material contains enough DNA. Kiwi fruit, strawberries and bananas are often recommended, but it is reported (see NCBE article Discovering DNA in the Links section) that the white strands produced here are usually pectin rather than DNA. Kiwi fruit temptingly contain protease that could help to digest the proteins surrounding DNA and make the addition of further protease unnecessary. Some foods (such as grapes) contain a lot of water and will make a watery ‘soup’. In this case, go back to the first step and add less water. You need an opaque cell ‘soup’ for good yields. The amount of DNA you will get will depend on the ratio of DNA to cell volume rather than the number of chromosomes in your material. Plant seeds (such as peas) contain a high proportion of DNA.

3 The salt added helps the DNA to precipitate (as it clumps together) when it meets the ethanol phase.

4 It is important to allow time for each step to complete. The detergent must sit for at least 5 minutes to disrupt the cell membranes and nuclear membranes.

5 If you don’t think you can see any DNA, dip your stick or rod into the surface of the ‘soup’ and then move it gently upward into the ethanol layer. Also, look closely at the ethanol layer for bubbles – sometimes clumps of DNA are loosely attached to the bubbles. If you can leave the mixture for 30-60 minutes, you may see more DNA precipitate.

6 Confirm that what you have is DNA by using a stain for DNA. (It may well be a mixture of DNA and RNA.) Confirm that what you have is not pectin by adding pectinase. If it dissolves it was pectin!

SAFETY: Wear eye protection when handling the enzyme solution.

Avoid skin contact with ethanol and with enzyme solutions or powders.

Wash any spills off your skin promptly.

Preparation

a Chill your ethanol by placing in a freezer for at least 2 hours, or overnight. Keep it on ice throughout the procedure ( Note 1 ).

Investigation

b Make a thick ‘soup’ by blending your source material with a little table salt and some cold water ( Notes 1, 2, 3 ). For example, use 100 cm 3 of split peas, with 200 cm 3 of cold water and a pinch of table salt (around 1 cm 3 – Note 2 ). Blend on high for 15 seconds.

c Strain your ‘soup’ through a mesh strainer and collect the liquid part in a beaker.

d Add 2 tablespoons (30 cm 3 ) of washing-up liquid and swirl to mix.

e Let the mixture settle for 5-10 minutes ( Note 4 ). Some protocols recommend carrying out this stage in a water bath at 60 °C. This may increase yield by increasing the breakdown of cell and nuclear membranes, or reduce yield if it stimulates the action of DNase enzymes ( Note 1 ).

f Pour the mixture into test tubes or other small glass containers, to make each about one third full.

g Add some protease enzymes to each test tube. You could use a pinch of meat tenderizer, a few drops of fresh pineapple juice, or some contact lens cleaning solution.

h Tilt your test tube to 45° and slowly pour well-chilled ethanol (IDA) into the tube so that it forms a layer on top of your ‘soup juice’ – about the same volume as you have of ‘soup/ juice’. Ethanol is less dense than water and will float on top. DNA is soluble in water, but salted DNA does not dissolve in ethanol and will form white clumps where the water and ethanol layers meet ( Note 5 ).

i Use a wooden stick or a straw (or a glass rod) to collect the DNA. Dip the stick into the tube and touch the white layer. Twirl the rod and the DNA should ‘spool’ onto the rod. DNA is a long, stringy molecule. As you pull on one end of the strand, it pulls more DNA into the ethanol layer where it will precipitate. ( Note 3 and 5 )

j Dry the sample on a paper towel if you want to measure the mass of product, or simply save the DNA by placing it in ethanol in any suitable small container with a lid.

Teaching notes

Each cell in the human body contains 46 chromosomes. If you unravelled the DNA from each chromosome and put the 46 segments end-to-end, each cell would contain about 2 metres of DNA. Each piece of DNA is around 4-5 cm long.

What happens at each step?

• blending with salt and water: breaks the cells apart from one another and increases the surface area exposed to reagents such as detergent. It also begins to disrupt some of the cell walls of plant material.
• adding salt: means the DNA is more likely to clump together when it meets the ethanol layer.
• adding meat tenderiser: meat tenderiser commonly contains bromelain or papain – protease enzymes extracted from pineapple and papaya respectively. It will digest proteins associated with the DNA and so may help to purify the sample.

Investigations:

• which sources give the most DNA? how will you measure the sources and the product accurately for comparison?
• do you get better yields if you keep things cool throughout, or if you heat the blended mixture with detergent at 60 °C?
• which detergent works best?
• does the meat tenderiser make a difference? with every source?
• try extracting DNA from things which might not contain it
• how could you prove that this was indeed DNA? (what is the effect on it of stains which act on DNA such as toluidine blue or acetic orcein?)

Several companies produce kits for DNA extraction (for example Edvotek and NCBE – links below). The advantage of using kits is that any enzymes, salts, surfactants and buffer solutions provided will be pre-tested to ensure consistency from batch to batch, and hence reliability of the outcome of the procedure. They will also probably be cheaper than if you tried to source such materials directly. For a simple ‘bulk’ extraction like this, using many domestically available chemicals, it may not be necessary to use a kit. However, if you want clean DNA for further analysis, the kits are recommended. Some kits allow students to extract DNA from their own cheek cells and to encapsulate that DNA in a small plastic pendant (on a chain). Many students respond very positively to this personal dimension in the protocol, and it may make the procedure more memorable.

Health & Safety checked, March 2009

learn.genetics.utah.edu This website provides a clear, simple procedure and useful FAQs.

www.edvotek.co.uk Edvotek is a biotechnology education company providing kits and workshops to support teaching and learning in biotechnology. They produce a simple DNA extraction kit (What does DNA look like?) and a kit (Genes in a tube) for extracting DNA from student cheek cells and making the sample of DNA (in a microcentrifuge tube) into a pendant.

www.ncbe.reading.ac.uk The NCBE has an international reputation for developing innovative educational resources and making sophisticated biotechnology techniques accessible to classroom teachers and students. They provide courses and materials for a wide range of biotechnology practicals – including a DNA pendant kit using which students can store the DNA collected from their own cheek cells in a glass vial. Their website also contains a link to a protocol for extracting DNA from frozen peas (at www.ncbe.reading.ac.uk/NCBE/PROTOCOLS/unpublished.html ).

The article Discovering DNA (in particular a paragraph headed DNA your onions?) on the NCBE site ( www.ncbe.reading.ac.uk/DNA50/peadna.html ) explains that fruits yield pectin rather than DNA.

(Websites accessed October 2011)

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4.2: DNA Extraction

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Background Information

Within the chromosomes of organisms, specific sections of DNA, called genes, code for specific proteins. A gene is “read” through a process of transcription to generate a sequence of mRNA. The mRNA is then used as the blueprint instructions to generate a specific protein during a process called translation. The process of generating a protein from a gene is often referred to as gene expression (Figure 1). A change, or mutation, in DNA can generate a protein that has a different amino acid sequence and therefore an altered or malfunctioning protein. Mutations in DNA of human chromosomes that cause malfunctioning or absent proteins are often the cause of genetic diseases. This lab discusses biotechnological advances that are used to detect and treat genetic diseases, advance agriculture or treat infectious diseases.

Figure 1. Gene expression. The process of transcription generates mRNA from a gene. mRNA undergoes translation to generate a protein. A change in the DNA sequence can alter the amino acid sequence of the protein and therefore can change or stop the function of the protein.

The first step in working with nucleic acids (DNA and RNA) is to remove the molecules from inside the cell. Different types of cells need to be processed differently in order to release nucleic acids. All cells have a cell membrane , a phospholipid bilayer that separates the internal environment of the cell from the external environment. In eukaryotes, DNA is housed inside the nucleus of the cell which is surrounded by the nuclear membrane , a second double-layered membrane, also composed largely of lipid molecules. When extracting DNA from plant cells, the cell wall must also be considered; some types of plant tissue require grinding or flash-freezing in order to break the tough cell wall.

In the DNA extraction procedure, plant cell walls and cell membranes are broken down by blending or mashing the cells. There are two key ingredients in the DNA extraction buffer aside from the water: dish soap (detergent) and salt . The detergent in the extraction buffer solution acts to dissolve phospholipids that form the cell membrane and the nuclear membrane. When the phospholipid membranes are dissolved, the cell lyses and releases the cellular contents, including DNA. The salt has two functions in the extraction process. It helps to neutralize the charge on the sugar-phosphate backbone, making DNA less soluble in water and allows it to more easily precipitate when the alcohol is added. The salt also helps to remove the proteins that are bound to the DNA and to keep the proteins dissolved in the lysis solution. The technique of filtration uses a medium, in this case, cheesecloth, to separate solids from liquids. The resultant material is referred to as filtrate. When cold ethanol is added to the filtrate, DNA precipitates at the water/ethanol interface. Although an individual DNA molecule is not visible with the naked eye, DNA isolated from large quantities of cells can be observed.

This protocol for extraction of DNA is based largely on the principle of solubility . Solubility refers to the ability of one substance (the solute) to dissolve in another substance (the solvent). Polar substances dissolve easily in polar solvents, but do not dissolve easily in nonpolar solvents, a phenomenon commonly referred to as “like dissolves like.” Water is a polar solvent, and molecules that dissolve easily in water are referred to as hydrophilic . DNA molecules are hydrophilic because the sugar-phosphate backbone of the molecules is highly polar. This means that DNA dissolves in water, so in this experiment, the DNA that is released when the cells are crushed dissolves in the juice/extraction buffer mixture.

Although the chemical reactions described above are all happening when you add the buffer and crush the food (strawberries), they are not visible with the naked eye. However, the addition of the cold ethanol caused a much more dramatic result! Ethanol is a nonpolar solvent, and when it is added to the juice extract, the DNA precipitates out of the solution. A precipitation reaction is a chemical reaction that causes a solid substance to emerge from a liquid solution. In this experiment, the addition of ethanol to the reaction forces the DNA to precipitate out of solution, which we can then spool onto the wooden stirrer or glass rod.

Exercise 1: DNA Extraction

Materials needed

• Isopropyl alcohol 91% (rubbing alcohol) or 95% ethanol, Chilled in the freezer
• Graduated cylinders
• Cheesecloth
• Dishwashing liquid (preferably, Dawn)
• Wide-mouth glass test tubes
• Disposable plastic cups
• Microcentrifuge tubes
• Wooden stirrer or glass rod
• Resealable plastic bag
• 100 or 200 mL beaker
• Ice buckets with ice
• strawberries
• ground flax seed
• ground wheat germ

Preparation

• Have isopropyl alcohol (rubbing alcohol) or ethanol cooled in an ice bucket ● Prepare your food item if needed (i.e. remove green strawberry tops, peel banana, grind wheat germ, etc)
• If not already made, prepare DNA extraction (lysis) buffer by combining the following: • 45 mL DI water
• 5 mL liquid dish soap
• 0.75 g NaCl (table salt)
• Place the food item (i.e 2 large strawberries) into the plastic zipper bag. Seal it and gently smash the food with your hands for about 2 minutes. Completely crush the food (strawberries) to disrupt the cells.
• Open the plastic zipper bag and add 10 mL of the DNA extraction (lysis) buffer. Squeeze the bag to remove all air and seal the bag tightly.
• Gently (to prevent over-sudsing or excessive foaming), but thoroughly, continue to crush the food (strawberries) inside the bag for about one minute or until it is a slushy consistency.
• Completely line the funnel with a layer of cheesecloth. Place the funnel into the wide-mouth test tube.
• Pour the food juice/DNA extraction buffer mixture into the funnel so the juice passes through the cheesecloth and into the test tube. Use the cheesecloth to strain the mixture so that only the juice flows into the tube and the pulp is retained in the cheesecloth.
• Discard the cheesecloth and the pulp. Remove the funnel from the tube. The glass tube now contains a liquid called “filtrate”.
• Carefully and slowly pipette an equal volume of ice-cold ethanol on top of the filtrate in the test tube using the plastic transfer pipette. The alcohol is less dense than the filtrate and will float as a layer on top of the filtrate. Do not mix or stir!
• Hold the tube still at eye level and observe what happens at the interface of the alcohol and the filtrate. DNA will precipitate at the alcohol-lysis buffer interface. This means it will come out of solution into a “solid” form and appear as fluffy white cotton or cloudy material. Verify with your instructor that you have isolated DNA.
• (optional) Use your wooden stirrer or glass rod to transfer your extracted DNA into a microcentrifuge tube. Add a small amount of ethanol to the tube to prevent your DNA from drying out.

Questions for Review

• What reagent in the extraction buffer functions to dissolve membranes?
• What reagent in the extraction buffer precipitates DNA so that it can be seen with the naked eye?
• What reagent in the extraction buffer functions to remove proteins from DNA?

January 31, 2013

Squishy Science: Extract DNA from Smashed Strawberries

A genetically geared activity from Science Buddies

By Science Buddies

Key concepts DNA Genome Genes Extraction Laboratory techniques

Introduction Have you ever wondered how scientists extract DNA from an organism? All living organisms have DNA, which is short for deoxyribonucleic acid; it is basically the blueprint for everything that happens inside an organism’s cells. Overall, DNA tells an organism how to develop and function, and is so important that this complex compound is found in virtually every one of its cells. In this activity you’ll make your own DNA extraction kit from household chemicals and use it to separate DNA from strawberries.     Background Whether you’re a human, rat, tomato or bacterium, each of your cells will have DNA inside of it (with some rare exceptions, such as mature red blood cells in humans). Each cell has an entire copy of the same set of instructions, and this set is called the genome. Scientists study DNA for many reasons: They can figure out how the instructions stored in DNA help your body to function properly. They can use DNA to make new medicines or genetically modify crops to be resistant to insects. They can solve who is a suspect of a crime, and can even use ancient DNA to reconstruct evolutionary histories!

To get the DNA from a cell, scientists typically rely on one of many DNA extraction kits available from biotechnology companies. During a DNA extraction, a detergent will cause the cell to pop open, or lyse, so that the DNA is released into solution. Then alcohol added to the solution causes the DNA to precipitate out. In this activity, strawberries will be used because each strawberry cell has eight copies of the genome, giving them a lot of DNA per cell. (Most organisms only have one genome copy per cell.)

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Rubbing alcohol

Measuring cup

Measuring spoons

Dishwashing liquid (for hand-washing dishes)

Glass or small bowl

Cheesecloth

Tall drinking glass

Three strawberries

Resealable plastic sandwich bag

Small glass jar (such as a spice or baby food jar)

Bamboo skewer, available at most grocery stores. (If you use a baby food or short spice jar, you could substitute a toothpick for the skewer.)

Preparation

Chill the rubbing alcohol in the freezer. (You’ll need it later.)

Mix one half teaspoon of salt, one third cup of water and one tablespoon of dishwashing liquid in a glass or small bowl. Set the mixture aside. This is your extraction liquid. Why do you think there is detergent in the extraction liquid?

Completely line the funnel with cheesecloth. Insert the funnel tube into the tall drinking glass (not the glass with the extraction liquid in it).

Remove and discard the green tops from the strawberries.

Put the strawberries into a resealable plastic sandwich bag and push out all of the extra air. Seal the bag tightly.

With your fingers, squeeze and smash the strawberries for two minutes. How do the smashed strawberries look?

Add three tablespoons of the extraction liquid you prepared to the strawberries in the bag. Push out all of the extra air and reseal the bag. How do you think the detergent and salt will affect the strawberry cells?

Squeeze the strawberry mixture with your fingers for one minute. How do the smashed strawberries look now?

Pour the strawberry mixture from the bag into the funnel. Let it drip through the cheesecloth and into the tall glass until there is very little liquid left in the funnel (only wet pulp remains). How does the filtered strawberry liquid look?

Pour the filtered strawberry liquid from the tall glass into the small glass jar so that the jar is one quarter full.

Measure out one half cup of cold rubbing alcohol.

Tilt the jar and very slowly pour the alcohol down its side. Pour until the alcohol has formed approximately a one-inch-deep layer on top of the strawberry liquid. You may not need all of the one half cup of alcohol to form the one-inch layer. Do not let the strawberry liquid and alcohol mix.

Study the mixture inside of the jar. The strawberry DNA will appear as gooey clear/white stringy stuff. Do you see anything in the jar that might be strawberry DNA? If so, where in the jar is it?

Dip the bamboo skewer into the jar where the strawberry liquid and alcohol layers meet and then pull up the skewer. Did you see anything stick to the skewer that might be DNA? Can you spool any DNA onto the skewer?    

Extra: You can try using this DNA extraction activity on lots of other things. Grab some oatmeal or kiwis from the kitchen and try it again! Which foods give you the most DNA?

Extra: If you have access to a milligram scale (called a balance), you can measure how much DNA you get (called a yield). Just weigh your clean bamboo skewer and then weigh the skewer again after you have used it to fish out as much DNA as you could from your strawberry DNA extraction. Subtract the initial weight of the skewer from its weight with the DNA to get your final yield of DNA. What was the weight of your DNA yield?

Extra: Try to tweak different variables in this activity to see how you could change your strawberry DNA yield. For example, you could try starting with different amounts of strawberries, using different detergents or different DNA sources (such as oatmeal or kiwis). Which conditions give you the best DNA yield?

Observations and results Were you able to see DNA in the small jar when you added the cold rubbing alcohol? Was the DNA mostly in the layer with the  alcohol and between the layers of alcohol and strawberry liquid?

When you added the salt and detergent mixture to the smashed strawberries, the detergent helped lyse (pop open) the strawberry cells, releasing the DNA into solution, whereas the salt helped create an environment where the different DNA strands could gather and clump, making it easier for you to see them. (When you added the salt and detergent mixture, you probably mostly just saw more bubbles form in the bag because of the detergent.) After you added the cold rubbing alcohol to the filtered strawberry liquid, the alcohol should have precipitated the DNA out of the liquid while the rest of the liquid remained in solution. You should have seen the white/clear gooey DNA strands in the alcohol layer as well as between the two layers. 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! (“Octoploid” means they have eight genomes.)

More to explore Do-It-Yourself Strawberry DNA, from the Tech Museum of Innovation, Stanford School of Medicine About Genetics , from the Tech Museum of Innovation, Stanford School of Medicine DNA Extraction Virtual Lab, from Learn Genetics, the University of Utah Do-It-Yourself DNA , from Science Buddies

This activity brought to you in partnership with  Science Buddies

DNA EXTRACTION

LEARNING OBJECTIVES

Extract DNA from plant cells.

Explain the purpose of each step in DNA extraction.

MCCCD OFFICIAL COURSE COMPETENCIES

Compare and contrast prokaryotic cell and eukaryotic cells.

Compare and contrast the physiology and biochemistry of the various groups of microorganisms.

Strawberries yield more DNA than any other fruit because they are octoploid which means they have eight of each type of chromosome. Other fruit options include peeled kiwi, papaya, banana, and mango.

Store the isopropyl alcohol in the freezer for at least 60 minutes prior to use (overnight will produce significantly better results).

PHOTO REQUIREMENTS

Take a photo with your photo ID during the lab exercise when you see this icon.

Paste the photo into the DNA Extraction Questions Document.

introduction

Nucleic acids are one of the macromolecules of life along with carbohydrates, proteins, and lipids. Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are nucleic acids. Like all macromolecules nucleic acids are made of building blocks or monomers. The monomer of nucleic acids is nucleotides. Nucleotides are composed of deoxyribose sugar, a phosphate group, and a nitrogenous base. There are four nitrogenous bases in DNA:  adenine, guanine, cytosine and thymine. In DNA adenine pairs with thymine and cytosine pairs with guanine. DNA is a double stranded molecule that resembles a spiral staircase. The sides of the staircase are composed of deoxyribose and phosphate groups. Each step of the spiral staircase is made of two nitrogenous bases. DNA is present in every cell. In a prokaryotic cell DNA is located in the cytoplasm. In a eukaryotic cell DNA is located in the nucleus.

Flow of information from DNA–>RNA–>PROTEIN is the central dogma of biology. A dogma is a principle or set of principles laid down by an authority as incontrovertibly true. Flow of information in a cell explains how DNA becomes E. coli , a herpes virus, Giardia lamblia , or you. The process of DNA being converted to mRNA is known as transcription. In transcription one of the two DNA strands will serve as a template to produce single stranded mRNA. The process of mRNA being converted to protein is known as translation. In translation the mRNA sequence is “read” three nucleotides (codon) at a time. Each codon specifies a particular amino acid. The mRNA sequence is thus used as a template to assemble the chain of amino acids that form a protein.

The first step in obtaining DNA from any organism is to release the DNA from a cell. In this lab we will be extracting DNA from soft fruit. Mashing the fruit helps break down cell walls and cell membranes. We will then add DNA extraction solution that contains detergent and salt. The detergent in the DNA extraction solution helps to dissolve the cell membrane thus releasing DNA, RNA, and proteins from inside of the cell. DNA has a negative charge due to the phosphate groups present in DNA. DNA molecules repel each other due to their overall negative charge. Think about how magnets repel if you try to push together two of the same poles. When salt is added, the positively charged sodium ions are attracted to the negative charges of the DNA molecule, neutralizing the negative charge of the DNA. This allows the DNA molecules to come together instead of repelling each other. When molecules are soluble, they are dispersed in the solution and are therefore not visible. When molecules are insoluble, they precipitate (clump together) and become visible. DNA is soluble in water but not in alcohol; therefore, when alcohol is added, it forces the DNA out of the solution. Molecules are less soluble at lower temperatures, so we chill the alcohol to get more of the DNA to precipitate. In this experiment, you will use soft fruit (strawberries, kiwi, mango, banana, papaya) to extract DNA.

Read all instructions carefully before you start the experiment.

Experiment Video Guide

1. If you are using strawberries, cut the green stem off the top, use the knife to chop the berries into small pieces. If you are using a banana, peel the banana, use the knife to chop half the banana into small pieces. If you are using two kiwi, peel the kiwi. Use the knife to chop the kiwi into small pieces. If you are using papaya or mango, peel the fruit. Using the knife chop half of the papaya or mango into small pieces.

2. Add the chopped fruit to the resealable bag and close the bag.

3. On a hard surface like a tabletop or counter, mash the fruit in the bag for 2 minutes. Do not mash the fruit too close to the bag’s seal, this could cause the seal to open and the fruit to squirt out and make a mess.

4. Measure a 1/4 cup of HOT water, add it to the bag and close the bag.

5. Measure 1/2 teaspoon of salt, add it to the bag and close the bag.

6. Gently mix and slosh the salt, water, and fruit together for 2 minutes. Try to not make bubbles.

7. Measure 1/4 teaspoon of dish detergent ( or laundry detergent or liquid soap or shampoo or body wash), add it to the bag and close the bag.

8. Gently mix and slosh the salt, water, fruit, and detergent together for 1 minute. Try not to make bubbles or have the mixture become foamy.

9. Place a piece of paper towel (or a coffee filter) into a small cup. Fold the top of the paper towel (or coffee filter) over the rim of the cup and secure it with a rubber band.

10. Carefully pour some of the contents of the bag into the paper towel (or coffee filter). Let it sit for several minutes until the liquid has dripped into the cup. You may use a spoon to gently stir the fruit mash to increase the speed of the liquid drip. Be careful do not rip the paper towel (or coffee filter). Repeat this process until all the contents of the bag have dripped through the paper towel (or coffee filter).

11. Dispose of the zipper bag and paper towel (or coffee filter) in the trash.

12. Remove the alcohol from the freezer. Tilt the cup containing the fruit mash. Slowly pour an equal amount of ice cold isopropyl alcohol down the side of the cup so that the isopropyl alcohol forms a layer on top of the fruit mash. Do not stir anything! Let the cup sit at room temperature for up to 30 minutes. You will see white strands come together and float to the top of the alcohol. This is the DNA.

14. Pour the contents of the cup down the sink. Let the water run for at least 30 seconds to dilute the alcohol.

DISCOVERIES IN MICROBIOLOGY

DR. BRUCE AMES

Do you prefer to buy products not tested on animals?  The Ames test was developed by American biochemist Dr. Bruce Ames in the 1970’s to determine if a chemical is a mutagen. The Ames test uses a mutant strain of Salmonella that cannot produce the amino acid histidine. If the chemical reverses the mutation, it is a mutagen of Salmonella . The chemicals that are mutagenic by the Ames test may be further tested on animals to assess their ability to cause mutations/cancer in humans.

Hands On Microbiology Copyright © 2022 by Jill Raymond. All Rights Reserved.

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DNA Extraction Lab: Extracting DNA from Strawberries and Other Fruit

Categories STEM Activities

One of my favorite science experiments is the DNA extraction lab where kids learn how to extract DNA from strawberries or another fruit. NGSS has it as a high school activity, but I routinely do it as part of middle school STEM activities and even with elementary kids.

I think it’s really fun for kids of all ages and really dives into the lab work part of science in a safe way.

Keep reading to learn how extracting DNA from fruit works!

What is a DNA Extraction Lab?

In this experiment, you are extracting DNA from fruit! It’s a multi-step science experiment that you can use to explore what DNA strands look like up close!

Strawberries are often used because they have a lot of DNA that is easily extractible. You might not get as much DNA using another fruit, but any fruit will work!

DNA Lab NGSS Alignment

Technically, the NGSS alignment for this activity is high school. But I use it in middle school and elementary all the time.

It’s OK to go rouge sometimes!

HS-LS3-1. Ask questions to clarify relationships about the role of DNA and chromosomes in coding the instructions for characteristic traits passed from parents to offspring. 

Although the NGSS alignment for this lesson is high school, I find that kids of all ages love doing DNA extraction.

How to Extract DNA from Cells

Follow along with this video and the experiment below to learn how to extract DNA from fruit.

DNA Lab Science

The science behind the DNA extraction experiment is simple. DNA is coded into every cell in any living organism so it can replicate.

Normally, DNA strands are tightly woven inside of a cell, but with a combo of soap and salt, the cell walls are broken down and the DNA strands are released.

The alcohol then lifts the DNA strands from the rest of the cells isolating them so the DNA can be examined.

DNA Extraction Lab Hypothesis

There are a few hypotheses you can apply to this science lab.

• Is it possible to isolate DNA from cells?
• Is there a difference in how much DNA is extracted depending on soap type?
• Does the DNA of all fruits look the same?
• Which type of fruit produces the largest amount of DNA strands?

Any of these questions are a great place to start!

DNA Extraction Lab Supplies

Shop these Amazon affiliate links for everything you need to do the fruit DNA lab!

DNA Extraction Lab Lesson Plan

Grab the lesson plan for this experiment below!

How to Extract DNA from a Strawberry or Another Fruit

Here is how to extract DNA from a strawberry! Kids will have a lot of fun with this hands-on science lesson.

Before getting started, put a 1/4 cup of rubbing alcohol into the freezer.

First cut up your fruit into tiny pieces.

Next, line a jar or cup with a plastic baggie and add the berries.

Add a tablespoon of dish soap and a teaspoon of salt. Add 1/3 of a cup of water.

Seal up your bag and squish all the ingredients together until it makes a pulp.

Place a coffee filter over the top of your jar to make a filter. You may find it helpful to hold it in place with a rubber band.

Pour the goo over the filter into the jar to isolate the juice.

Pour the juice into your test tube.

Cover the juice with a 1-inch layer of rubbing alcohol.

Watch as a snotty substance rises to the top of the rubbing alcohol. This is the DNA!

Use an eyedropper to isolate the DNA strands and examine it with a microscope.

More Middle School Science Activities

Leaf Chromatography Experiment for Elementary and Middle School

How to Make Cloud Bread- At-Home Kitchen STEM!

Laminar Flow Science Experiment with a Balloon

Charcoal Water Purification

Share this project with a friend!

• Virtual Labs

DNA Extraction

DNA is extracted from human cells for a variety of reasons. With a pure sample of DNA you can test a newborn for a genetic disease, analyze forensic evidence, or study a gene involved in cancer. Try this virtual laboratory to perform a cheek swab and extract DNA from human cells.

Try It Yourself!

To learn how to do DNA extraction yourself, use the link in the grey box above the virtual lab.

Supported by a Science Education Partnership Award (SEPA) Grant No. R25RR023288 from the National Center for Research Resources.

The contents provided here are solely the responsibility of the authors and do not necessarily represent the official views of NIH.

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How to Extract DNA From Human Cheek Cells

It’s easy to extract DNA from human cheek cells. You don’t even need a lab. Here’s how to do this experiment in your kitchen.

What Is DNA?

DNA is deoxyribonucleic acid. It’s the genetic material in every cell in your body, except mature red blood cells, which have lost their cellular nuclei. DNA codes for proteins, which are used to build structural material, such as teeth and bones, and also cells, which combine to form tissues and organs. Your DNA is unique to you!

Materials for DNA Extraction

• sodium chloride (table salt)
• liquid soap or detergent
• distilled water
• rubbing alcohol
• yourself or a volunteer
• a scale and a measuring cup or beaker for small volumes

How to Extract DNA

• First, you want to make an 8% salt solution. This means you dissolve 8 grams of salt in 92 milliliters of distilled water. If the salt won’t dissolve, you can microwave it for a few seconds to warm the water.
• In another container, mix together 25 milliliters liquid soap with 75 milliliters distilled water.
• Pour 10 milliliters of water into a cup. Swirl this water around in your mouth for 30 seconds to a minute.
• Spit the water into a small cup.
• Pour 1 milliliter of your salt solution into the cup.
• Add 1 milliliter of the liquid soap solution.
• Gently swirl the contents of the cup to mix them together.
• Pour 5 milliliters of rubbing alcohol down the side of the cup so that it slowly flows into the liquid.
• Within a few minutes, the DNA will rise to the surface of the cup as a cloudy, slimy-looking substance.
• Pour 1 milliliter of alcohol into a small, clear container (a test tube is great, if you have one handy).
• Use a glass rod or plastic toothpick to remove the DNA from its container. Do this by twirling the rod into the DNA, like twirling spaghetti onto a fork.
• Dip the rod into the container of alcohol. You may need to swish it around gently to dislodge the DNA you just extracted. That’s it!
• If you want more DNA, you can repeat the earlier steps and add the new DNA to the same final container. You’ll need to swish the water around in your mouth longer to get a good sample. Or, if you don’t really care about having the same DNA, add a sample from someone else’s mouth.

You can examine the DNA more closely using a magnifying glass or a microscope. The same process works with other types of cells. Try extracting DNA from a banana .

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Nucleic acid extraction is a common yet critical task in the molecular biology lab. Also known as nucleic acid isolation or nucleic acid purification, removal of genetic material from the sample matrix is the first step in many genetic and genomic studies. Preparing high quality samples improves the likelihood that your experiment will work and you’ll get the results you need.

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Nucleic acid extraction methods

Nucleic acid extraction and isolation starts with disrupting the cellular structures containing the genetic material—nuclei, ribosomes, bacteria, viruses; this is usually accomplished by adding a compatible detergent, mechanical disruption, and/or heat.

From there, several methods for nucleic acid purification are common. Each nucleic acid isolation method is based on a different biochemical principle. Selection of a method is based on the throughput required, equipment available in the lab, or the degree of purity required.

Tools for nucleic acid extraction and isolation

KingFisher Purification Systems

PureLink RNA Mini Kit

mir Vana miRNA Isolation Kits

Organic extraction and precipitation

Nucleic acid isolation by organic extraction involves addition of phenol and guanidine isothiocyanate to separate the DNA, RNA, and proteins into different organic phases. Organic extraction is a low-cost method, and with advanced reagents such as TRIzol , is a straightforward process requiring very little equipment.

Silica-based nucleic acid isolation

Nucleic acids bind to silica (also known as glass fibers) under high-salt conditions and can be released under low-salt conditions. Silica-containing columns provide an easy way to bind, wash, and elute purified nucleic acids from multiple clarified cell lysates in parallel.

Invitrogen Purelink  and GeneJET  columns are designed to flow buffers through centrifugation, vacuum, or gravity. Most protocols use spin column technology to take advantage of readily available lab equipment. Spin plates provide a high-throughput format based on the same isolation principle.

Paramagnetic bead-based nucleic acid purification

In this method paramagnetic (attracted to magnet) beads are added to the sample, and nucleic acids bind to the beads. Using a strong magnet, the beads are held in place while removing unwanted material. After washing, the genetic material is eluted from the beads in water or a low-salt buffer.

Magnetic bead isolation is now one of the most popular nucleic acid extraction methods due to its scalability and automation compatibility; MagMAX Bead Kits  and KingFisher Sample Purification Systems  are designed to work together to efficiently purify a variety of nucleic acids.

Instruments, kits, and reagents for a variety of nucleic acid extraction and purification techniques

Our nucleic acid extraction instruments, kits and reagents are optimized to provide maximum yield, purity, and integrity from virtually any sample type. Whether you need to extract and purify RNA, viral nucleic acid, DNA fragments, plasmid DNA, or genomic DNA, Thermo Fisher Scientific has a solution.

Genomic DNA extraction

Sensitive, scalable genomic DNA purification products help maximize your efficiency.

RNA extraction

Select RNA extraction kits based on your application, sample, or RNA type.

Plasmid DNA purification

Isolate, purify, and extract high-quality plasmid DNA for cloning or transfection.

Automated nucleic acid purification

Efficiently perform DNA, RNA, viral nucleic acid, and plasmid isolation with MagMAX kits and KingFisher automated nucleic acid purification systems.

Viral nucleic acid purification

Purify viral DNA and RNA with excellent reproducibility from a variety of sample types.

PCR & agarose gel cleanup

Purify DNA fragments with simple, rapid PCR and gel cleanup kits.

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