Do-It-Yourself DNASummary Time Required Very Short (≤ 1 day) Prerequisites None Material Availability Readily available Cost Very Low (under $20) Safety No issues Abstract All living things have DNA inside their cells. How do scientists extract the DNA from cells in order to study it? In this experiment you can make your own DNA extraction kit from household chemicals and use it to extract DNA from strawberries. Objective In this experiment, you will design a DNA Extraction Kit and use it to purify DNA from strawberries. Background Introduction All living things come with a set of instructions stored in their DNA, short for deoxyribonucleic acid. Whether you are a human, rat, tomato, or bacteria, each cell will have DNA inside of it. DNA is the blueprint for everything that happens inside the cell of an organism, and each cell has an entire copy of the same set of instructions. The entire set of instructions 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. They can genetically modify foods to be resistant to insects. They can figure out the suspect of a crime. They can even use ancient DNA to reconstruct evolutionary histories! How do scientists get the DNA out of a cell so that they can study it? This is called a DNA extraction, and there are many DNA extraction kits available from biotechnology companies for scientists to use in the lab. During a DNA extraction, a detergent will cause the cell to pop open, or lyse, so that the DNA is released into solution. Then the DNA can be precipitated out of the solution by adding alcohol. In this experiment you will make your own DNA extraction kit from household materials and use it to purify DNA from strawberries. Strawberries are octoploid, which means they have eight copies of the DNA in their genome in every cell! Why use strawberries to test your DNA extraction kit? Because strawberry cells each have eight copies of the genome in every cell! When an organism has eight copies, called an octoploid, it has a lot more DNA per cell than an organism that only has one copy. Using DNA from strawberries will help you have a successful DNA preparation so you can purify a lot of DNA. Materials and Equipment Measuring cup Measuring spoons 1/2 cup rubbing alcohol 1/2 teaspoon salt 1/3 cup water 1 tablespoon dishwashing detergent (Dawn®) Glass or small bowl Cheesecloth Funnel Tall drinking glass 3 strawberries (green tops removed) i plastic sandwich bags Test tube or small glass jar (e.g., spice jar) Bamboo skewer (find them at the grocery store) Experimental Procedure 1. Chill the rubbing alcohol in the freezer. (You'll need it later.) 2. Mix the salt, water, and Dawn detergent in a glass or small bowl. Set the mixture aside. This is your extraction liquid. 3. Line the funnel with the cheesecloth, and put the funnel's tube into the glass. 4. Put the strawberries in the plastic bag and push out all the extra air. Seal it tightly. 5. With your fingers, squeeze and smash the strawberry mixture for 2 minutes. 6. Add 3 tablespoons of the extraction liquid you made in Step 2 to the strawberries in the bag. Push out all the extra air and reseal the bag. The liquid detergent will help break the strawberry cells open allowing the DNA to spill out. The salt helps create an environment where the different strands of DNA can gather together in a clump making it easier for you to see them. 7. Squeeze the strawberry mixture with your fingers for 1 minute. 8. Pour the strawberry mixture from the bag into the funnel. Let it drip into the glass until there is no liquid left in the funnel. 9. Throw away the cheesecloth and the strawberry pulp inside. Pour the contents of the glass into the test tube or small glass jar so it is 1/4 full. 10. Tilt the test tube or jar and very slowly pour the cold rubbing alcohol down the side. The alcohol should form a one-inch deep layer on top of the strawberry liquid. If you have a small test tube or container you will not need all of the alcohol. (Don't let the alcohol and strawberry liquid mix. The DNA collects between the two layers!) DNA does not dissolve in alcohol. When alcohol is added to the mixture, the rest of the mixture, except for the DNA, stays in solution, while the DNA precipitates out into the alcohol layer—that’s the gooey clear/white stuff you can collect with a skewer or other thin rod. 11. Dip the bamboo skewer into the test tube where the alcohol and strawberry layers meet. Pull up the skewer. The whitish, stringy stuff is DNA containing strawberry genes! Variations You can try these steps to purify DNA from lots of other living things. Grab some oatmeal or kiwis from the kitchen and try it again! Which foods give you the most DNA? 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 bamboo skewer using milligrams before and after the DNA purification. Then subtract the starting weight from the final weight to get your final yield in milligrams (mg). Compare your yield in milligrams (mg) under various experimental conditions: o Start with different amounts of strawberries— i i? o Change some of the components of your kit— will other detergents work better? o Start with different materials— are there other sources of DNA with higher yields? Molecular Scissors Summary Time Required Very Short (≤ 1 day) Prerequisites None Material Availability Readily available Cost Very Low (under $20) Safety No issues Abstract Ever used a pair of molecular scissors? Restriction enzymes are molecular scissors that cut DNA into pieces. Find out which enzymes will cut, and where by making a restriction map. Then you can figure out what will happen if you change the sequence of the DNA. Will the same enzymes still cut the new DNA sequence? Objective In this experiment you will determine if cutting a piece of DNA with a restriction enzyme depends upon the sequence of the DNA. Introduction All living things come with a set of instructions stored in their DNA, short for deoxyribonucleic acid. Whether you are a human, rat, tomato, or bacteria, each cell will have DNA inside of it. DNA is the blueprint for everything that happens inside the cell of an organism, and each cell has an entire copy of the same set of instructions. The entire set of instructions is called the genome and the information is stored in a code of nucleotides (A, T, C, and G) called bases. Here is an example of a DNA sequence that is 12 base pairs long: Notice that this piece of DNA has two sequences: one on the top and one on the bottom. DNA is double stranded, which means that it has two strands. The nucleotides of each of these strands are paired together in a particular way to match the other strand: A pairs with T and C pairs with G. If a nucleotide is paired according to these rules, it is called a match. But if the nucleotide is not paired properly, then it is called a mismatch. The information stored in the DNA is coded into sets of nucleotide sequences called genes. Each gene is a set of instructions for making a specific protein. The protein has a certain job to do, i a function. Since different cells in your body have different jobs to do, many of the genes will be turned on in some cells, but not others. For example, some genes code for proteins specific to your blood cells, like hemoglobin. Other genes code for proteins specific to your pancreas, like insulin. Even though different genes are turned on in different cells, your cells and organs all work together in a coordinated way so that your body can function properly. What if there is something wrong with one of your genes? This can cause problems for your body and how it functions. For example, people who have type I diabetes have problems making insulin. To help people with diabetes, scientists figured out a way to make insulin that diabetics can inject into their body. The insulin is made by a bacteria that has the human gene for insulin. For scientists to study a gene, they need to be able to isolate it. The simplest way to isolate a gene is to cut it out and clone the gene into a small piece of bacterial DNA called a plasmid. How do you cut out a piece of DNA? A restriction enzyme is a protein that acts like a pair of molecular scissors to cut a DNA strand. The enzyme recognizes a certain DNA sequence where it will cut the DNA apart. Here is an example of a restriction enzyme called EcoRI that cuts DNA at a particular sequence, creating sticky ends: (Image from Biotechnology Online, 2007) Once the DNA is cut apart, it can be put back together in different ways. For example, the gene for human insulin can be cut out and then recombined with the DNA of a bacteria. Then the bacteria can grow and make human insulin for people who need it to manage their diabetes. Cutting DNA apart using restriction enzymes is a very important step in the discovery and manufacturing of genes that become important pharmaceuticals, like the insulin gene. In this experiment, you will investigate how restriction enzymes recognize different DNA sequences. You will use a computer program to generate random pieces of DNA sequence. Then you will use another program to test your sequence and look for restriction enzymes that will cut it (often called cutters). By comparing which restriction enzymes cut each unique DNA sequence, you can determine if changing the DNA sequence will change the restriction enzymes that cut it. If the DNA sequence does not affect the restriction enzyme that cuts it, then the different DNA sequences will have a lot of cutters in common. If the DNA sequence does affect the restriction enzyme that cuts it, then the different DNA sequences will have more unique cutters than common cutters. Materials and Equipment A computer with internet connection Java-based web browser Lab notebook and pencil Printer Scissors Glue Experimental Procedure 1. The first step is to make a piece of DNA using the Random DNA Sequence Generator. 2. Enter "20" in the box for the Size of DNA in base pairs (bp), and leave the setting for the GC content at 0.50 (which will give you half G+C and half A+T). 3. Click the generate button and you will get a random piece of DNA shown in the text box: 4. Double click in the text box to select your DNA sequence, then copy it to the clipboard by selecting "Edit" and then "Copy" from your file menu. 5. The next step is to check your piece of randomly generated DNA to see which restriction enzymes will cut it using the NEBcutter program from New England Biolabs, a company that happens to sell (you guessed it) restriction enzymes! 6. Click inside the text box and paste your DNA sequence from the clipboard by selecting "Edit" and "Paste" from the file menu. Leave all of the other settings to the default settings. 7. Click the "Submit" button and you will get a page showing your piece of DNA and one or more enzymes that cut it. This is called a restriction enzyme map. Each arrow is a place where the enzyme will cut the DNA. Each restriction enzyme has a name that is written in code, for example EcoRI. You can click on a name to get more information about that enzyme. Also, notice that there is an arrow on both the top and bottom strand of DNA: 8. Print this page, cut it out, and paste it into your lab notebook for your records. Make an alphabetical list of the enzyme(s) that cut the DNA. 9. Now you are ready to repeat steps 1–8 with a new DNA sequence. Just go back to the Random DNA Sequence Generator and start over. 10. Repeat this experiment at least five different times. Each time you will make one new piece of DNA and test it for cutters by making a restriction enzyme map. 11. Compare all of your sequences and the restriction enzyme maps, then ask yourself some questions: o Is there an enzyme which shows up in more than one map? o Is there any enzyme which shows up on all of the maps, that your DNA sequences have in common? o Is there as sequence that only cuts one of the DNA i is unique? 12. Draw a circle around any restriction enzymes which are common in all of the DNA sequences you tested. Count them and write the number in your lab notebook. 13. Draw a square around any restriction enzyme which is unique to one of the DNA sequences you tested. Count them and write the number in your lab notebook. 14. In this experiment, you have collected a lot of data in your notebook. Now you need to analyze your data and put it together into a story. The first step is to make a summary table of your experiment. Here is a sample summary table that you might want to use for this experiment: Name of How Many Restriction How Many are How Many are Sequence Enzymes Cut? Unique? Common? DNA#1 DNA#2 DNA#3 DNA#4 DNA#5 15. Now you can make some graphs to show your data. For this experiment, you can make a bar graph to show the number of unique and common restriction enzymes for each DNA sequence you tried. 16. Now make your conclusion by relating your results to your objective. Are there more unique cutters, or more cutters in common for the different DNA sequences? Did changing the DNA sequence change the restriction enzymes that cut the DNA? Do you think that restriction enzymes are unique to specific DNA sequences? Variations Instead of generating a brand new random sequence each time, you can also make changes to the DNA sequence yourself. You can make subtle changes, or dramatic changes. You can try to add or change restriction enzyme sites. How will these kinds of changes affect your restriction map? You can test whether the length of the DNA will change the number of restriction enzymes that cut it. Just change the size of DNA in bp in step one from 20 bp to test a series of DNA sizes. Try 20 bp, 40 bp, 60 bp, and 100 bp. Which has more cutters, long sequences or short sequences? Some enzymes cut in the same place as other enzymes. By looking at the sequence of the cut site, can you explain why? Try comparing the cut site of restriction enzymes that cut in the same places as other restriction enzymes. What do you see? Sometimes, two restriction enzymes leave ends that can stick together. These are called sticky ends, and will match up to another piece of DNA with matching ends. Can you figure out how to use this experiment to generate different pieces of DNA and then put them together? Bubble-ology Summary Time Required Very Short (≤ 1 day) Prerequisites None Material Availability Readily available Cost Low ($20 - $50) Safety No issues Abstract Making your own bubble solution is fun, but sometimes the bubbles don't seem to work as well as the solutions you buy in the store. In this experiment you can test if adding corn syrup or glycerin to your bubble solution will make it just as good as the stuff you can buy. This experiment will have you blowing bubbles! Objective In this experiment you will test if adding glycerin or corn syrup will improve a mixture of bubble solution. Introduction Everybody loves bubbles! But what makes bubbles form, and float up in the air until they pop? A soap bubble (Wikipedia Commons, 2006). The secret to a good bubble is something called surface tension, an invisible bond that holds water molecules together. Water is a polar molecule, so it has plus and minus ends just like magnets that attract each other. When the water molecules align with each other they stick together, creating surface tension. You might think that it is the surface tension of the water that holds the skin of a bubble together. Actually, the surface tension of water is too strong to make a bubble. You can try yourself to blow a bubble with plain old water, it just won't work! A good bubble solution has a detergent added to it to relax the surface tension of the water, allowing it to have more elastic, stretchy properties. Now it can act more like the skin of a balloon, stretching out nice and thin, trapping air inside of the bubble like a liquid balloon. What do you need to make a good bubble solution at home? The basic ingredients are water and detergent. In this experiment, you will add glycerin or corn syrup to see if they can help you make better bubbles. Which solution will make the biggest bubbles? Which bubbles will last the longest? Materials and Equipment Glass mason jars with lids (recycled jars work great) Measuring cups and spoons Distilled Water Liquid dishwashing soap (e.g. Dawn®) Glycerin, small bottle (available at a drugstore or pharmacy) Light corn syrup Pipe cleaners Permanent marker Stopwatch Experimental Procedure 1. First, make your bubble solutions, and store them in clearly labeled glass mason jars. Use one jar for each different solution and label with the formula using a permanent marker. Here are three basic solutions to try, but notice that the total volume of the solution is kept consistent: Solution #1 Solution #2 Solution #3 Ingredient detergent only detergent + glycerin detergent + corn syrup 1 cup (240 mL) + Water 1 cup (240 mL) 1 cup (240 mL) 1 Tbsp (15 mL) Detergent 2 Tbsp (30 mL) 2 Tbsp (30 mL) 2 Tbsp (30 mL) Glycerin ----- 1 Tbsp (15 mL) ----- Corn Syrup ----- ----- 1 Tbsp (15 mL) 2. Now make a pipe cleaner wand for each solution. Pinch a pipe cleaner in the middle and give it a kink. Bend one half of the pipe cleaner into a circle and twist together at the center. Repeat with the other two pipe cleaners, and check that all three circles are the same diameter. 3. Go outside and test your bubble solutions. Blow a bubble and catch it on your wand. Immediately start the stopwatch and time how long the bubble lasts. This will take some practice, so try it out on some extra solution before you start! 4. Repeat the experiment as many times as possible for each solution. 5. Record your data in a data table: Solution #1 - Solution #2 - Solution #3 - Bubble Time (secs) Bubble Time (secs) Bubble Time (secs) Trial 1 Trial 2 ....... Trial 20 TOTAL Average Bubble Time in Seconds 6. For each bubble solution, calculate the average time in seconds that the bubbles lasted. Do this calculation by adding up all of the data for a solution, and dividing by the number of trials for that solution. 7. Make a graph of your data. For each solution, make a bar of the average time in seconds that the bubble lasted. 8. Analyze your data. Which formula worked the best? Variations In this experiment, you investigated the presence or absence of an additive like glycerin or corn syrup. What about the concentration? If you are good at timing bubbles, you can try this experiment using different concentrations of glycerin or corn syrup in your solutions. How little is too little, and how much is too much to add? Do bubbles always make a spherical shape? Try twisting pipe cleaners into different shapes, like: stars, squares, and triangles. What shape will the bubbles be? What happens when three or more bubbles come together? See if you can design an experiment to test the idea that three or more bubbles will always meet at a 120 degree angle. Have you ever tried Magic Bubbles? They are bubbles that resist evaporation, and are so stable that you can even touch them without popping. The secret to this formula is that a polymer (an elastic molecule) has been mixed into the solution which adds to the elastic properties of the bubble while helping to prevent evaporation. Try adding your own secret ingredients to your bubble mix. Does it change the physical properties of the bubble? Here are a few suggestions: o A small amount of glue, like white glue or gel glue o Different combinations of food coloring o Some scented oils Bouncy Polymer Chemistry Summary Difficulty Time Required Very Short (≤ 1 day) Prerequisites None Material Readily available Availability Cost Very Low (under $20) Adult supervision required. Borax is harmful if swallowed. On rare occasion handling Safety borax can result in rashes. Abstract Have you ever wondered how fun toys like Silly Putty, Gak, and Slime are made? These products are so much fun because of the properties of polymers, which make them delightfully bouncy, stretchy, sticky, moldable, breakable, hard, soft, and just plain fun! In this science project you can be the developer of your own putty product by changing the ratio of ingredients to change the physical properties of your putty polymer. By describing the physical properties of your results, you can choose the best recipe for your new product. Objective Determine the best recipe for your own homemade silly putty by varying the ratio of ingredients and by observing physical properties. Introduction You might think that chemists are a bunch of boring scientists who wear lab coats and look at beakers all day, but did you know that many toys you play with are made using chemistry? Some of your favorite toys like Gak, Slime and Silly Putty started out as chemistry experiments. In fact, some of your favorite toys may have been invented by chemists who work for toy companies like: Crayola, Play-Doh or Mattel. Chemistry is the study of matter, and how matter behaves and interacts with other kinds of matter. There are many different kinds of matter, which can be described using the concept of properties. Toys like silly putty are unique because they have distinct properties that are different from the properties of other types of matter. There are two different kinds of properties, chemical properties and physical properties. Chemical properties are qualities that can be observed during a chemical reaction, like when vinegar reacts with baking soda. Physical properties are qualities that can be observed during a physical change, like the melting of an ice cube. Physical properties can be used to describe the state of some matter, which can be a solid, liquid or a gas. The physical and chemical properties of Silly Putty are what make it so much fun because it is a polymer that is stretchy and bouncy! But Silly Putty is not the only polymer. Polymers are actually found in a many different materials, which have a broad range of properties. Materials made from polymers can be found naturally, such as amber and natural rubber, or generated synthetically, in a laboratory, such as nylon, silicone, and all plastics. Scientists use chemical and physical properties to describe all of the unique qualities of a chemical or a mixture of chemicals, which can also be called a solution. To do this they use descriptive language, or words that are used to describe objects. Some descriptive words used to describe a chemical might be: hot, cold, squishy, hard, soft, crystalline, granular, smooth, liquid, clear, opaque, runny. There are many different qualities to be described. You just need to find the right words to use. The unique physical and chemical properties of a polymer or mixture can be changed by the amount of each different ingredient used to make them. Sometimes the amount of one ingredient compared to the amount of another ingredient can make a big difference. This is called a ratio, and a ratio can be useful to know how much of each ingredient to add to your mixture so you will end up with a mixture that has desirable properties. In this science project you will change the ratio of two basic ingredients in homemade Silly Putty. These ingredients are Borax and Elmer’s glue (both diluted in water). Elmer's glue is made up of a synthetic polymer called polyvinyl acetate, which has many small chemical groups called acetates. Borax (a white powder made up of sodium tetraborate) can react with the acetates in Elmer’s glue. The end result of this chemical reaction is that many acetates link together, and this creates homemade Silly Putty! You will describe the physical properties of each different mixture using a data table. Then you will choose the ratio of ingredients to create the best putty product. Materials and Equipment Zip-lock baggie water Elmer's® School Glue Borax (also called 20-Mule Team household cleaner); See "Local Resources for Purchasing Common Chemicals" on our Guide to Purchasing Chemicals page. Safety Note: Borax is harmful if swallowed. It is uncommon, but possible, for borax to cause skin rashes. Gloves can be used to avoid skin contact. measuring cups and spoons two recycled glass jars with a lid permanent marker Disposable gloves, can be used if there is concern over handling borax. Disposable gloves can be purchased at a local drug store or pharmacy, or through an online supplier like Carolina Biological Supply Company. If you are allergic to latex, use vinyl or polyethylene gloves. Food coloring (optional) Experimental Procedure 1. First you will need to prepare the 50% glue solution, which is made up of half glue and half water. 2. Add one cup of glue and one cup of water to one of the jars. 3. Tightly secure the lid to the jar and shake until glue is fully diluted, and no gooey clumps remain. 4. Using a permanent marker, label this jar "50% Glue". 5. Next, you will make the Borax solution, which is made up of 4% Borax in water. Usually you would weigh the borax, but you can approximate this solution by adding 2 tsp Borax to 1 cup of warm water to a jar. 6. Tightly secure the lid to the jar and shake until no particles of Borax remain, and the solution is clear. 7. Using a permanent marker, label this jar "4% Borax". 8. Now we will add the 50% glue and 4% Borax solutions together in different ratios, to see what properties the final mixture will have. First need to make a data table in your lab notebook like Table 1 below. Physical 50% Glue Solution 4% Borax Solution Observations Properties 1 Tbsp 3 Tbsp 2 Tbsp 2 Tbsp 3 Tbsp 1 Tbsp 5 Tbsp 1 Tbsp Table 1. To write down your observations and results, you can use a table like this one. 9. For each mixture, first add the correct amount of the 50% glue solution to a Zip-lock baggie. 10. Then add the corresponding amount of the 4% Borax solution to the baggie. 11. Seal the baggie, and using your fingers squish the mixture around to mix together the ingredients. a. For fun: Try adding food coloring to the mixtures before mixing. Make sure to add the same amount of food coloring to each mixture so that the coloring is a controlled variable. 12. Write down your observations in your data table. 13. When the mixture begins to form a sticky glob, you can take it out of the baggie. 14. Write down your description of the physical properties of the material in your table. Remember to use words like runny, slimy, sticky, hard, soft, bouncy, etc. 15. Which ratio of ingredients produced the best product? What will you call your new product? 16. Cleanup Tip: If you have leftover 50% Glue or Glue/Borax mixtures, do not pour them down the drain. They can cause clogs. Instead, throw them in the garbage. Variations Are there other ways to change the recipe in order to change the physical properties of the putty? Try changing the percentages of glue or Borax in the solutions to see how that changes your product. Can you optimize the recipe in new and different ways to obtain different types of products? Another polymer is the protein gelatin found in Jello. What experiments can you conduct to explore the physical properties of gelatin? A common use for polymers is to make thin sheets of material for holding things, for example plastic shopping bags, garbage bags, Zip-lock baggies or balloons. Can you design a series of experiments to test these different materials? Are some materials stronger, or more puncture resistant? How do the properties of the material make it a good useful product? Turn Milk into Plastic! Summary Difficulty Time Required Very Short (≤ 1 day) Prerequisites None Material Availability Readily available Cost Very Low (under $20) Safety This science project uses hot liquids. Adult supervision and/or help is needed. Abstract "Plastic made from milk" —that certainly sounds like something made-up. If you agree, you may be surprised to learn that in the early 20th century, milk was used to make many different plastic ornaments —including jewelry for Queen Mary of England! In this chemistry science project, you can figure out the best recipe to make your own milk plastic (usually called casein plastic) and use it to make beads, ornaments, or other items. Objective In this chemistry science project, you will investigate which is the best recipe for making plastic out of milk. Introduction What can you make out of milk? Cheese, butter, whipped cream, sour cream, yogurt, ice cream, and...plastic! Are you surprised by plastic? It is true. In fact, from the early 1900s until about 1945, plastic made from milk was quite common. This plastic, known as casein plastic or by the trade names Galalith and Erinoid, was used to manufacture buttons, decorative buckles, beads, and other jewelry, as well as fountain pens and hand-held mirrors and fancy comb-and-brush sets. Figure 1 below shows examples of belt buckles made from casein plastic in the 1930s and '40s; more examples can be found in the references in the Bibliography. Figure 1. These decorative belt buckles were all manufactured from casein plastic in the 1930s and '40s. (Photograph courtesy of Galessa's Plastics Photostream, 2007) But how can milk be changed into plastic? To answer that we need to think first about what plastic is. The word plastic is used to describe a material that can be molded into many shapes. Plastics do not all look or feel the same. Think of a plastic grocery bag, a plastic doll or action figure, a plastic lunch box, and a disposable plastic water bottle. They are all made of plastic, but they look and feel different. Why? Their similarities and differences come from the molecules that they, like everything else, are made of. Molecules are the smallest units (way too small to see with your eye!) of any given thing. Plastics are similar because they are all made up of molecules that are repeated over and over again in a chain. These are called polymers, and all plastics are polymers. Sometimes polymers are chains of just one type of molecule, as in the top half of Figure 2 below. In other cases polymers are chains of different types of molecules, as in the bottom half of Figure 2, that link together in a regular pattern. A single repeat of the pattern of molecules in a polymer (even if the polymer uses only one type of molecule) is called a monomer. Figure 2. The top image shows a polymer where the monomers are just one type of molecule. The bottom image shows a polymer where the monomers are made up of three different molecules. In both polymers, the monomers link in a repeating pattern. Milk contains many molecules of a protein called casein. When you heat milk and add an acid (in our case vinegar), the casein molecules unfold and reorganize into a long chain. Each casein molecule is a monomer and the polymer you make is made up of many of those casein monomers hooked together in a repeating pattern like the top (all pink) example in Figure 2.. The polymer can be scooped up and molded, which is why it is a plastic. In this chemistry science project, you will investigate what is the best recipe for making casein plastic by making batches of heated milk with different amounts of vinegar. How much vinegar is needed to give you the most plastic? Without enough vinegar the casein molecules do not unfold well, making it difficult for them to link together into a polymer. Of course, if you were manufacturing you would be thinking about both the amount of plastic you can make and the cost. The more of any ingredient you use the more expensive the end product is. The "best" recipe will have the highest yield (make the most plastic) for the smallest amount of vinegar. The plastic you make will be a bit more crumbly and fragile than Galalith or Erinoid. That is because the companies that made those casein plastics included a second step. They washed the plastic in a harsh chemical called formaldehyde. The formaldehyde helped harden the plastic. Although you will not use formaldehyde because it is too dangerous to work with at home, you will still be able to mold the unwashed casein plastic you make. Once you have a recipe, with the best ratio of vinegar to milk, for your casein plastic, you can have fun with it. Try shaping it, molding it, or dyeing it to make beads, figures, or ornaments, such as those shown in Figure 3 below. Figure 3. The casein plastic you will make in this project can be used to make beads, figures, or ornaments like the ones shown here Materials and Equipment The materials listed below are for doing the experimental procedure exactly as written. However, you can make changes to the experimental procedure in order to use a different size measuring cup and/or a stovetop rather than a microwave. Mugs or other heat-resistant cups (4); they should all be identical so as not to introduce another variable (See Variables in Your Science Fair Project), and large enough to hold more than 8 oz. of liquid Masking tape Pen or permanent marker Teaspoon measuring spoon White vinegar (at least 8 oz.) Milk (at least 12 cups); nonfat, 1%, 2%, and whole milk will all work Microwavable liquid measuring cup; should be large enough to hold 4 cups of milk like this one from Amazon.com Microwave Cooking or candy thermometer, such as this one from Amazon.com Spoons (4) Cotton cloth (12 squares, each 6 x 6 inches); cutting up old T-shirts works just fine Rubber bands (4) Clear plastic or glass drinking cups (4), each large enough to hold 8 oz. of liquid Kitchen scale, should be accurate to 1 gram, such as this one from Amazon.com Wax paper (in 12 identical pieces); each piece should be smaller than the weighing surface of the kitchen scale Paper towels Lab notebook Optional (for fun): molds, cookie cutters, food coloring, paint, glitter, permanent markers Experimental Procedure Making Casein Plastic This experiment uses hot liquids, so an adult's help will be needed throughout. 1. Using the masking tape and pen, label the four mugs: 1, 2, 4, and 8. 2. Use the measuring spoon to add 1 teaspoon (tsp.) of white vinegar to the mug labeled "1," 2 tsp, to the mug labeled "2," 4 tsp. to the mug labeled "4," and 8 tsp. to the mug labeled "8." 3. Heat 4 cups of milk (1 quart) in a large measuring cup in the microwave. a. The exact amount of time needed will depend on your microwave. Start by warming the milk at 50% power for five minutes. The 50% power will help you avoid scalding (burning) the milk. b. Have an adult check the milk with a thermometer to make sure it is at least 49°C (120°F). If it is not heated enough, put it back in the microwave for another two minutes at 50% power. Repeat this step until the milk is hot. Warmer than 49°C is fine. c. In your lab notebook write down the total number of minutes it took you to warm the milk and the final temperature of the hot milk. When you repeat these steps later you should try to get as close to these numbers as possible. 1 or 2 degrees warmer or cooler is fine as long as the milk is at least 49°C. 4. Carefully pour 1 cup of hot milk in to each of the four mugs with vinegar in them. (You may need to ask an adult to pour the hot milk for you.) What do you see happening in each mug? Write down your observations in a data table, like Table 1 below, in your lab notebook. In at least one of the mugs you should see that the milk has separated into white clumps (called curds). a. Make sure to pour the milk in to all four of the mugs at the same time so that the milk is the same temperature across all four vinegar amounts. Number teaspoons Forms curds? Describe liquid Weight of casein Write down any other of vinegar (yes/no) after sieve plastic (in grams) observations 1 2 4 8 Table 1. Make a table like this in your lab notebook to write down your data. Make a new table for each repeat of this experiment, for a total of three tables. 5. Mix each mug of hot milk and vinegar slowly with a spoon for a few seconds. That will help make sure the vinegar reacts with as much of the milk as possible. 6. Meanwhile, take one of the cotton-cloth squares and attach it with a rubber band to the top of one of the clear cups so that it completely covers the cup's opening. This will make a sieve as shown in Figure 4 below. a. Make sure the cloth hangs down a bit inside the cup so that you have room to pour liquid in. b. Repeat this step with the other three clear cups. c. Label the clear cups 1, 2, 4, and 8 with the tape and pen. 7. Once the milk and vinegar mixture has cooled a bit, carefully pour the mixture from mug "1" into the cotton cloth sieve on cup "1." If there are any curds, they will collect in the cloth sieve. The leftover liquid will filter into the clear cup. Figure 4 below shows what the setup looks like. Where do you think the casein is, in the liquid in the cup or the curds in the sieve? Tip: You may want to do this step over a sink just in case any of the liquid spills. Figure 4. A piece of cotton cloth and a rubber band are used to make a sieve at the top of a clear glass. Once the milk and vinegar mixture is poured into the sieve, the curds will gather on the top of the sieve, and the liquid will drain through into the clear cup. 8. In your table in your lab notebook, write down what the leftover liquid in the clear cup looks like. What color is it? How clear is it? Be sure to write the information down for each cup on the corresponding line on the table (for instance, cup "1" for the cup with 1 tsp. of vinegar, and so on). 9. Over a sink, carefully remove the rubber band sieve on cup "1." With your hands, squeeze all the extra liquid out of the curds. Scrape the curds off of the cloth and knead them together, as you would bread dough, into a ball. This is your casein plastic. Before it dries, the ball of dough will look similar to Figure 5 below. Figure 5. The wet casein plastic will form a lumpy ball of whitish dough like the one shown here. 10. Weigh the ball of casein plastic on a kitchen scale (set for grams) using a piece of wax paper to keep the scale clean. Record the weight in your table. a. When weighing, remember to turn on the scale and first make sure it reads zero with nothing on it. This will help make sure your measurements are accurate. Also, use a new sheet of wax paper each time you weigh a different ball of casein plastic. This will give you exact weights (without crumbs and liquid from the last ball) b. The amount of casein plastic each recipe makes is called the yield for that recipe. The more plastic, as measured by weight in this case, the greater the yield. 11. Repeat steps 7-10 for the other three mugs of milk and vinegar. 12. If you want to make your casein plastic into something, you can color, shape, or mold it now (within an hour of making the plastic dough) and then leave it to dry on some paper towels for at least 48 hours. See the "Ideas for Fun with Casein Plastic" for more suggestions. 13. For your science project you will want to repeat steps 1-11 again two more times. This will give you enough data to see whether one recipe reliably yields more casein plastic than another. Analyzing Your Data 1. Calculate the average yield (amount in grams) of casein plastic made from each recipe. If you do not know how to average, ask an adult to show you. 2. Make a bar graph showing the average yield for each recipe. You can make the bar graph by hand or use a website like Create A Graph to make the graph on the computer and print it. a. On the left axis (the y-axis) write the average yield of casein plastic. Make a bar along the x-axis for each of the four recipes you tested. 3. When you look at your observations about the liquid left over after straining out the curds, do the weights of the yields make sense? Why or why not? 4. Which recipe yielded the most casein plastic on average? Was any other recipe a close second? Based on this data, which do you think is the "best" recipe in terms of yield? Ideas for Fun with Your Casein Plastic Try making beads, ornaments, or figurines out of your casein plastic. You should do the molding and coloring steps (except for paint and/or marker) within the first hour of making the plastic or it will start drying out. 1. Shaping the plastic: a. Knead the dough well before shaping it. b. Molds and cookie cutters work well on the wet casein plastic. c. You can also sculpt the wet casein plastic into figures, but it takes a bit more patience. 2. Coloring the plastic: a. Food coloring, glitter, or other decorative bits can be added to the wet casein plastic dough. The beads in Figure 3 above were made from casein plastic dough that had yellow food coloring and multicolored glitter kneaded into it. b. Dried casein plastic can be painted or colored on with markers. The smiley face in Figure 3 is on uncolored casein plastic and was drawn on using a black permanent marker. 3. Hardening the plastic: a. Casein plastic will be hard once it has dried. b. Drying time varies depending on the thickness of the final item (thicker pieces take longer), but most casein plastic requires at least two days to become hard.