Name Period Date The Chemistry of Carbohydrates Biologists today depend upon chemists for much of their understanding of life and life processes. Therefore, an understanding of some chemical concepts important to living things is necessary. Carbohydrates make up a large group of chemical compounds found in cells. Carbohydrates are used for both energy and structural support in living organisms. In this investigation, it is expected that you: apply information about water to answer questions about carbohydrates. distinguish between models used in the lab and actual chemical formulas of molecules. determine the molecular characteristics of carbohydrates. Materials: carbohydrate models your cerebral lobes PART A. Water Information can be gained from examination of the chemical formula of water, H 2 0. 1. What elements make up water? 2. What does the number 2 following the H tell you? 3. Why does oxygen NOT have a subscript? 4. How many molecules of water are represented by the formula H 2 0? 5. What is a molecular formula? 6. What is the molecular formula of water? 7. What is a structural formula? This is the structural formula of water. 8. What do the lines between the O and the H in the structural formula of water represent?
PART B: Carbohydrates An important group of biological compounds are the saccharides, or more commonly, carbohydrates. Carbohydrates contain carbon (C), hydrogen (H), and oxygen (O). The many different types of sugars have been grouped into three main categories: monosaccharides, disaccharides, and polysaccharides. Monosaccharides or Simple Sugars The prefix mono means one. Monosaccharides are sugars that are made up of only one molecule. Thus, they are called single or simple sugars. The one molecule of a monosaccharide can, however, have different shapes due to a different arrangement of the atoms. Three examples of monosaccharides are glucose, fructose, and galactose. Examine the structural formulas for the three monosaccharides below. 9. What three elements are present in monosaccharides? 10. How many atoms of carbon are present in each molecule of glucose? in each molecule of fructose? in each molecule of galactose? 11. Add the subscripts to the following to indicate the proper chemical formulas. Do this by counting the total number of carbon, hydrogen and oxygen atoms in each molecule in the structure. a. glucose: C H O b. fructose: C H O c. galactose: C H O 2
12. What is the ratio of hydrogen atoms to oxygen atoms in monosaccharides? 13. What is the ratio of hydrogen atoms to oxygen atoms in water? 14. The structural arrangement of C, H, and O in glucose, fructose and galactose differs. How does this difference help to explain why different model shapes are used for each monosaccharide in your carbohydrate kits? 15. Molecules of monosaccharides may have the same molecular formula but differ in three-dimensional structure. This is called isomerism. Describe isomerism in your own words using the structural formulas and the models as a guide. Disaccharides or Double Sugars Two monosaccharide sugar molecules can join together chemically to form a larger carbohydrate molecule called a disaccharide, or double sugar. The prefix di means two. By chemically joining a glucose molecule with a fructose molecule, a double sugar called sucrose is produced. Use the models in your kit to illustrate this process. To make a glucose molecule add an -H piece and an -OH piece to the end of the glucose shape. Do the same to the fructose shape to make a fructose molecule. Now attempt to join the glucose to the fructose. 16. Does the model interlock like a puzzle? In order to join the molecules properly, remove an -OH end from the glucose and an -H end from the fructose. Now fit the glucose piece into the fructose piece. 17. With the-oh and -H pieces removed do the pieces fit more securely to make sucrose? 18. The OH and H ends that were removed can also fit together to form a molecule. This molecule has hydrogen atom(s) and oxygen atom(s). 19. This molecule has the chemical formula and is called. The process of putting together two smaller organic compounds into one larger compound with the removal of water is called dehydration synthesis. 3
20. Write the molecular formula for the sucrose molecule that you just created by adding the proper subscripts below. (Think about what two molecules you joined together to make the sucrose. Refer back to number 11 for some guidance and remember that one molecule of H 2 0 was lost.) sucrose: C H O Construct another disaccharide called maltose by joining together two glucose molecules together. Follow the same procedure as before by adding the H piece and OH piece to the ends of both glucose molecules. Now remove the H and OH pieces to ensure a proper fit between the two glucose molecules. 21. Write the molecular formula for the maltose that you just created by adding the proper subscripts below. (Think about what two molecules you joined together to make the sucrose. Refer back to number 11 for some guidance and remember that one molecule of H 2 0 was lost.) maltose: C H O 22. The disaccharide lactose forms when a glucose molecule joins with a galactose molecule. Determine the molecular formula for lactose. (Again, refer back to number 11 if necessary and don t forget the lost H 2 0.) lactose: C H O 23. Determine the ratios of hydrogen atoms to oxygen atoms for both the sucrose and maltose molecules you made. How does the ratio of H to O atoms compare: a. in sucrose, maltose and lactose? b. in glucose and fructose? c. in water? 24. Does isomerism exist in double sugars? Compare your sucrose model with the maltose model. 25. How many monosaccharide molecules are needed to construct a disaccharide molecule? 4
Polysaccharides or Complex Sugars Just as double sugars were formed from two single sugar molecules, polysaccharides form when many single sugars are joined together chemically. The prefix poly means many. Starch, glycogen and cellulose are the three most common polysaccharides in biology. They consist of long chains of glucose molecules joined together. Construct a starch molecule by joining three glucose molecules together the same way you did when making a disaccharide. This will represent only a small portion of a starch molecule because starch consists of hundreds of glucose molecules. Before beginning, be sure to reattach the H and OH ends to each glucose molecule. 26. What must be removed from some of the glucose molecules in order to join them properly? 27. Recall what this process is called. 28. Determine the molecular formula of your starch molecule. (Remember to subtract H and OH pieces that you removed when inserting your subscripts.) starch: C H O 29. Compare the ratio of H and O atoms a. in starch b. in disaccharides? c. in monosaccharides? d. in water? 5
Analysis 30. What 3 elements make up all carbohydrates? 31. What is the ratio of H to O atoms in carbohydrates and water? 32. What small molecules make up all disaccharides? 33. What small molecules make up all polysaccharides? 34. What common molecule is always formed when monosaccharides molecules are joined? 35. Mono means one, di means two, and poly means many. Why are these terms used in describing the three types of sugars? 36. Synthesis means putting together. Dehydration means loss of water. Explain why chemists refer to the joining of monosaccharides to form disaccharides as a dehydration synthesis reaction. 37. Why is the joining of three glucose molecules in forming a polysaccharide an example of dehydration synthesis? 38. The word carbohydrate is derived from carbon and water (hydrate). Explain why this combination correctly describes this chemical group. 39. Describe what your beautiful/handsome body would look like if you eat only Twinkies and drink only Pepsi (Sugar H 2 O) for the next 5 years. 40. Why would you look that way? 6