DNA Extraction. Teachers Guide Introduction:

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Jordan Hampton
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DNA Extraction Teachers Guide Introduction: Cells are the basic unit of life and make up all animals, plants and bacteria.

In the same way that animals have internal organs, like the heart, brain, eyes, and lungs, cells have their own miniature organs known as organelles. Each type of organelle has a different function.

molecules, known as macromolecules: Lipids, proteins, polysaccharides, and nucleic acids.

1 DNA Extraction Teachers Guide Introduction: Cells are the basic unit of life and make up all animals, plants and bacteria. A single cell is tiny around 1/500 th of a millimetre so small that the average human has 100 trillion cells in their body. In the same way that animals have internal organs, like the heart, brain, eyes, and lungs, cells have their own miniature organs known as organelles. Each type of organelle has a different function. Although there are many organelles (many more than shown in the diagram below), and although they are complicated systems, cells are composed almost entirely of just four main types of large molecules, known as macromolecules: Lipids, proteins, polysaccharides, and nucleic acids. Lipids can be thought of as fats or oils and make up the cell membrane, which acts as a kind of skin, holding and protecting the contents of the cell from its environment. Lipids also make up the nuclear membrane that surrounds the nucleus. Proteins are used by the cell to create enzymes, transport molecules, and to build structures. Polysaccharides are also known as carbohydrates or sugars, and perform a number of different roles in the cell including energy storage and the modification of proteins. Nucleic acids are used to store information most famously in the form of DNA (deoxyribose nucleic acid) which forms extremely long double-helix strands. DNA contains

the instructions for creating and controlling all aspects of the biology of every known living organism.

Humans have twenty-three pairs of chromosomes one chromosome from each pair is inherited from each parent. Chromosomes, made up of both DNA and proteins, are seen in the right hand image below.

You will be able to extract enough DNA to be visible to the naked eye (in clumps, not single strands).

2 the instructions for creating and controlling all aspects of the biology of every known living organism. In plants and animals the long DNA molecules are coiled around proteins to form chromosomes which are kept in the nucleus of the cell (as in the diagram below). Humans have twenty-three pairs of chromosomes one chromosome from each pair is inherited from each parent. Chromosomes, made up of both DNA and proteins, are seen in the right hand image below. This picture was captured using an electron microscope. This lab demonstration will show how to isolate DNA from strawberries using common materials. You will be able to extract enough DNA to be visible to the naked eye (in clumps, not single strands). Strawberries are a good DNA source for this work because they contain eight copies of each chromosome per cell, which is more than many other organisms. Strawberries are also soft and easy to smash, and produce some enzymes that help in breaking down the cell walls, so they are perfect for this experiment. Equipment and consumables: Resealable plastic bags Strawberries (fresh or frozen) Detergent or shampoo Table salt (NaCl) Water Plastic cups Coffee filter Ice cold isopropanol or rubbing alcohol (available from pharmacies) A stirrer (a teaspoon or a plastic stirrer)

Method: 1. Pull off any green leaves from the strawberries. 2. Put a strawberry in a plastic bag, seal it and gently smash the fruit for about 2 minutes, crushing the strawberry. 3.

3 Method: 1. Pull off any green leaves from the strawberries. 2. Put a strawberry in a plastic bag, seal it and gently smash the fruit for about 2 minutes, crushing the strawberry. 3. In a plastic cup, prepare DNA extraction solution: mix together 50 ml (about 3 tbsp) of water, 1 tsp of salt and 10 ml (2 tsp) of detergent or shampoo. 4. Add 5 ml (1 tsp) of the DNA extraction solution to the bag with the strawberry. Reseal the bag and gently smash the pulp for another 2 minutes (try to avoid making soap bubbles). 5. Add an additional 15 ml (3 tsp) of water to the strawberry mixture. Reseal the bag and mix for a further 30 seconds. 6. Place the coffee filter inside a plastic cup and pour the strawberry liquid into the filter. Gently squeeze the remaining liquid in the filter into the cup. The liquid will have DNA in it, but you won t be able to see it as it is dissolved in the water. 7. Pour 5 ml (1 tsp) of cold isopropanol or rubbing alcohol into the cup containing the strawberry liquid. Do not mix or stir. Wait a few seconds, and a white cloudy substance will form in the top layer of the solution (a precipitate). This is the isolated DNA! 8. Tilt the cup and pick up the DNA using a stirrer. How it works: Strawberries are a complicated mixture containing thousands of different substances; however, the majority of the material consists of the four major macromolecules: Lipids, proteins, polysaccharides, and nucleic acids. DNA is a nucleic acid, so we need to remove the lipids, proteins, and polysaccharides from the strawberries. Luckily, each type of

4 macromolecule has unique properties that we can exploit to separate them from the strawberry DNA. DNA is found in the nucleus of the cell this means that to extract DNA we have to break open the cell membrane and the nuclear membrane. Both the cell membrane and nuclear membrane are made of lipids molecules, which resemble fats or oils, arranged in a double-walled bilayer (see the image below). In the same way that dishwashing detergent is used to dissolve fats and oils from dirty dishes, we can use detergent to dissolve the lipid molecules in the strawberry mixture. Proteins are complicated molecules that have a large number of different functions in the cell. They are responsible for many of the active and functional parts of living cells, such as forming the enzymes that create or break down substances. Proteins embedded in the cell membrane can act as signal receptors and transport channels into the cell (see the diagram above). Proteins also play many structural roles such as forming the spool that coils DNA into chromosomes. To purify DNA we need to remove the protein. A simple way of purifying proteins is to add a large quantity of salt: this will precipitate the protein (make the protein insoluble) so that it will clump together; then we can remove it using the coffee filter. Polysaccharides, also known as carbohydrates, are large sugar molecules. They are used for energy, but also play a structural role forming the fibre that helps plants keep their shape. Polysaccharides are also used as part of a cellular sorting system: polysaccharide labels are attached to items depending on where in the cell they are to be located (see the diagram above). These labels are also used to signal when an item is to be broken down and recycled by enzymes. Polysaccharides are easy to remove from the strawberry mixture

5 either they are insoluble and will be removed by the coffee filter, or they are very soluble and will remain dissolved during the final step. The extraction solution you prepared contains detergent to remove the lipids and salt to precipitate the protein. Pouring the mixture through the coffee filter will remove the protein and the insoluble polysaccharide fibre, leaving a liquid containing the dissolved lipids, the soluble polysaccharides, and the DNA. The final step, adding the cold isopropanol, precipitates the DNA, allowing it to be scooped out, and leaves the lipids and the soluble polysaccharides dissolved in the remaining liquid. Ideas for further investigation: Strawberries work so well for this experiment because they have eight copies of each chromosome (this is referred to as being octoploid) other plants usually have fewer. Kiwifruit have six copies of each chromosome (hexaploid) while most banana varieties have three (triploid). Try extracting DNA from other plants or fruits use similar sized pieces for each of your samples and compare the amount of DNA you are able to extract.

The result; real DNA strands from a banana!

The result; real DNA strands from a banana! DNA (Deoxyribonucleic Acid) is the genetic instruction manual found in every living thing! DNA contains the information needed to make proteins, cells and organs. DNA is extracted from human cells for