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West Lothian Council Lorna C. Webster 1 Protein foods Proteins are important food chemicals that we can get from plants and animals. Our bodies need protein for growing and repairing damage. We can get protein into our bodies by eating the foods shown below. The foods shown above have all come from animals but some people are vegetarians and do not eat food that has come from animals. Vegetarians still need to eat protein because they still need to grow and repair their bodies. They need to eat lots of different plants to make sure they get enough protein. Soya is a protein that comes from a plant and it is used in different foods for example soya milk. Beans also contain protein. Write a heading and try the work below. 1. Why do our bodies need protein? 2. Make a list of foods that contain high levels of protein. Lorna C. Webster 2 3. Do vegetarians need to eat protein – explain your answer? 4. How do people who are vegetarians make sure they have enough protein in their diet? 5. List two foods that contain protein that comes from plants. 6. Copy and complete the table below. Name of food name of animal or plant it came from Steak Bacon Eggs Cheese Beans Milk Chicken Soya 7. Collect a data book and answer the questions below. a) What page would you look at to find out about how much protein there is in food? b) Which food contains the most protein per 100g? c) Which food contains the most fat per 100g? d) Which food contains the most carbohydrate per 100g? e) Which food contains no fat but 6g of carbohydrate per 100g? f) Which two foods contains no fat but 20g per 100g carbohydrates? g) Which food contains approximately the same amount of all three food chemicals? Lorna C. Webster 3 Testing foods for protein Read You may already know about testing foods: the benedict’s test turns from blue to orange if sugar is in food. the iodine test turns from brown to black if starch is in food. the filter paper test goes transparent if fat is in food. Chemists also have a way to test whether foods contain protein. This test is called the soda lime test. Watch your teacher demonstrate (demo 3.40) what happens in the soda lime test. Remember the pH paper must be moist because we need water present to test the pH of a substance. substance + soda lime moist pH paper Write a heading and try the work below. 1. What test is used to find out if a) sugar is in food? b) starch is in food? c) fat is in food? 2. What is the name of the test that is used to find out if protein is present in a substance? 3. Draw a diagram to show what is done in the soda lime test. Lorna C. Webster 4 4. Why does pH paper need to be moist? 5. What happened to the pH paper if the substance contained protein? 6. Does this mean that the gas made was acid, alkaline or neutral? 7. Copy and complete the sentences below. To test if a substance contains protein we add s____- l____ to it and heat it. If the pH paper turns _________ we know that protein is present. This means that an a__________ gas has been made in the reaction. Lorna C. Webster 5 Protein chemistry Read The diagram below shows the elements that are present in all proteins. N C H O Remember we are made of mainly water (60%) with some protein so our bodies contain the same elements as proteins. You may already know that starch is a very large molecule called a polymer made by joining lots of glucose molecules together. glucose glucose glucose glucose glucose glucose Proteins are also very large molecules called polymers. Proteins are made by joining lots of molecules called amino acids together. Amino acid Amino acid Amino acid Amino acid Amino acid Amino acid The reaction to join small molecules into polymers is called a polymerisation reaction. Lorna C. Webster 6 Write a heading and try the work below. 1. Use a data book and the chicken diagram on page 6 to make a list of the elements that you would find in a protein. 2. What elements do our bodies contain? Explain your answer. 3. Is a polymer a large molecule or a small molecule? 4. Explain how starch is made. 5. What are the small molecules called that join together to make a protein molecule? 6. Are proteins large or small molecules? Explain your answer. 7. Copy the diagram to show how a protein is made from amino acids joining together. 8. What is the name of the reaction that makes polymers like starch and protein? 9. Go to the amino acids display and look at the models of amino acids. Draw a picture of each molecule and beside it write the formula. Hint: Black = carbon Red = oxygen Blue = nitrogen White = hydrogen 10. Copy the revision box below and colour it in to make it stand out in your jotter. Polymerisation is the name of a chemical reaction to make large molecules by joining small molecules together. A polymerisation reaction is used to make proteins, starch and also plastics. Lorna C. Webster 7 The Protein problem Our bodies need certain amino acids to keep us healthy. We get these amino acids by eating protein in animal and plant foods. We have the same problem with eating protein as we do with eating starch. Protein molecules are too big to get into our blood. This means that our bodies have to break the proteins up into small amino acids. This is called digestion. amino protein acid The amino acids are small enough to get into our blood and travel to places where they are needed to make new proteins for example muscle protein, skin protein, nerve protein, kidney protein, enzyme protein. Write a heading and try the work below. 1. Why can protein molecules not get into our blood? 2. What is the process called that breaks big protein molecules up into amino acids? 3. Why can amino acids get into our blood? 4. Copy the blood and guts diagram. 5. What happens to the amino acids once they get into our blood? Lorna C. Webster 8