NAME:___________________________________________ PERIOD:______________

 

DATE:_________________________  DATE DUE: _____________________________

 

CHEMISTRY OF CARBOHYDRATES,

 PROTEINS AND LIPIDS

 

INTRODUCTION: Biologists today depend on chemists for much of their understanding of life and life processes.  Thus, an understanding of some chemistry of living things is necessary in order to truly understand living things.  Carbohydrates make up a large group of chemical compounds found in cells.  Carbohydrates are used by the cells as an energy source, or else are used in building cell structures.  Lipids are a part of all cellular membranes.  They may also be stored within a cell as energy food. Proteins form part of almost all structures within a cell.  Therefore, they are essential for cell growth and repair.

 

PURPOSE: The purpose of this exercise is to learn to interpret molecular formulas, and use models to interpret the structural formulas of some carbohydrates, lipids and proteins.

 

MATERIALS:

Scissors

Glue stick or tape

Carbohydrate model sheet

Lipid and protein model sheet

Blank paper

 

PROCEDURE:

PART A

The following questions apply to the chemical formula of water (H2O).

 

1. What elements make up water?

 

2. What does the subscript number 2 following the H in H2O tell you?

 

3. Why does oxygen not have a subscript number following it?

 

4. How many molecules of water are represented by the formula H2O?

 

 The structural formula of water is as follows:                  H         H

 

                                                                                                      O

 

5. What do the lines between O and H in the structural formula represent?

 

 

PART B:

Carbohydrates contain three different elements: carbon (C), hydrogen (H), and oxygen (O).  There are many different types of carbohydrates.  They have been place in to three groups: monosaccharides, disaccharides, and polysaccharides.

 

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 these three sugars and answer the following questions.

 

 

 

 

6. What three elements are present in glucose, fructose and galactose?

 

7. How many atoms of carbon are present in a molecule of glucose?

 

8. How many atoms of carbon are present in a molecule of fructose?

 

9. How many atoms of carbon are present in a molecule of galactose?

 

10. Add the subscripts to the following that indicate the proper chemical formula.  Do this by counting the total number of carbon, hydrogen and oxygen atoms in each molecule in the structural formulas above.

 

            a. glucose:   C ___       H ____                  O ____

 

            b. fructose:  C ___      H ____                  O ____

 

            c. galactose: C ___      H ____                  O ____

 

 

11. What is the ratio of hydrogen atoms to oxygen atoms in a molecule of water?

 

            (circle one)                  1:1       2:1       3:1

 

12. What is the ratio of hydrogen atoms to oxygen atoms for monosaccharides?

 

            (circle one)                  1:1       2:1       3:1

 

13. Compare the structural formula of glucose to fructose.  Are they exactly the same in shape?

 

14. Explain how glucose and fructose differ in their shape?

 

 

Two monosaccharide sugar molecules can join together chemically to from 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 paper models on the separate page to illustrate this process.

 

Cut out a glucose and a fructose paper model molecule from the page.  Cut along the solid lines only.  Attempt to join the two molecules together like puzzle pieces.

 

15. Do the glucose and fructose fit easily together to form a sucrose molecule?

 

In order to join the molecules, remove the –OH end from the glucose molecule and the –H end from the fructose molecule.  Cut along the dotted lines.  Now attempt to join the two molecules together like puzzle pieces. 

 

16. Do the glucose and fructose now fit easily together to form a sucrose molecule?

 

17. The –OH and the –H ends that were removed can also fit together with each other to form a molecule.  This molecule has ________ hydrogen atom(s) and  _______ oxygen atom(s). 

 

18. This molecule has the chemical formula _____________ and is called ___________.

 

The process of putting together two smaller organic compounds into one larger organic compound with the removal of water is called dehydration synthesis or condensation.

 

19. Write the chemical formula for glucose à   _________________________________

Write the chemical formula for fructose à  _________________________________  Add the subscripts together à                     C ___________ H ________O _______

Subtract two hydrogen and one oxygen à                              H     2         O      1

       Write in the correct subscripts à                  C ___________ H ________O _______

 

This is the chemical formula for sucrose.  Tape or glue your sucrose AND water molecules to a blank sheet of paper.  Label them sucrose and water respectively. Write the chemical formulas for sucrose and water under their names. 

 

Different disaccharide molecules can be made by joining other monosaccharides in different combinations.  By chemically joining a glucose molecule to another glucose molecule, maltose is formed.  By chemically joining a glucose molecule to a galactose molecule, lactose is formed. 

 

Just as double sugars were formed from two single sugar molecules, polysaccharides are formed 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 five glucose molecules together the same way you joined the disaccharide.  This will represent only a small part of a starch molecule because starch consists of hundreds of glucose molecules.

 

20. What must be removed form the ends of the glucose model molecules in order to have them easily fit together?

 

21. What is this process called?

 

The chemical formula for a polysaccharide is written as (C6H10O5)n   The n equals the number of C6H10O5 groups that joined together to from the polysaccharide.  Tape or glue your starch molecule and the molecules of water to the blank sheet of paper.  Label them starch and water respectively.  Write the chemical formulas for starch and water under their names.

 

PART C:

On a molecular basis, all fats are somewhat similar.  Just as carbohydrates are composed of monosaccharide molecules, all fats are composed of smaller molecules called glycerol and three fatty acids.  Examine the structural formula for glycerol and answer the following questions.

 

 

22. What elements are present in glycerol? 

 

23. Are there any elements in glycerol that are not in carbohydrates?

 

24. What is the chemical formula for glycerol?    C________ H ________  O _________

 

25. What is the ratio of hydrogen atoms to oxygen atoms in glycerol?

 

26. How does this ratio compare with the ratio in carbohydrates?

 

The second molecule which contributes to forming fats is a long molecule called a fatty acid.  Many different fatty acids exist, but all are similar in several ways.  Examine the structural formulas of the three examples of fatty acids below and answer the following questions.

 

 

27.  What elements are present in all fatty acids?

 

28. What is the chemical formula of butyric acid?  C ________  H ________ O ________

 

29. What is the chemical formula of caproic acid?  C ________  H ________ O _______

 

30. What is the chemical formula of lauric acid?  C ________  H ________ O ________

 

31. Is the ratio of hydrogen atoms to oxygen atoms the same in each fatty acid?  Explain your answer.

 

Note the end of butyric acid containing the oxygen atoms.  This special end arrangement of carbon, hydrogen and oxygen is called a carboxyl group.

 

32. Is the carboxyl group present in all the fatty acids shown?

 

 

A fat molecule consists of one glycerol molecule and three fatty acid molecules joined together.  Cut out the glycerol and fatty acid paper models.  Cut along the solid lines only.  Attempt to join the molecules together like puzzle pieces.

 

 

33. Do the glycerol and fatty acids fit easily together to form a fat molecule?

 

In order to join the molecules, remove the –OH ends from the glycerol molecule and the –H ends from each of the fatty acid molecules.  Cut along the dotted lines.  Now attempt to join the four molecules together like puzzle pieces. 

 

34. Do the glycerol and fatty acids now fit easily together to form a fat molecule?

 

35. How many molecules of glycerol are in one fat molecule?

 

36. How many molecules of fatty acids are in one fat molecule?

 

37. What chemical substance is formed when the –OH and –H ends are joined?

 

38. How many water molecules are formed when one fat molecule is produced?

 

39. What is the process called when you put together smaller molecules to form a larger molecule with the removal of water?

 

40. Write the chemical formula for glycerol à   _________________________________

Write the chemical formula for butyric acid à  ______________________________

Write the chemical formula for caproic acid à ______________________________

Write the chemical formula for lauric acid à _______________________________ Add the subscripts together à                     C ___________ H ________O _______

Subtract six hydrogen and three oxygen à                             H     6         O      3

       Write in the correct subscripts à                  C ___________ H ________O _______

 

This is the chemical formula for this fat molecule. Tape or glue your fat molecule and the molecules of water to the blank sheet of paper.  Label them fat and water respectively.  Write the chemical formulas for the fat and water under their names.

 

PART D:

Carbohydrates consist of many monosaccharides joined together while fats consist of glycerol and fatty acid molecules joined together.  Proteins also consist of smaller molecules called amino acids joined together.  There are twenty different amino acids that make up proteins.  Examine the structural formulas for the four representative amino acids below and answer the following questions.

 

 

 

41. What elements are present in the amino acids?

 

42. Are there any elements in the amino acids that are not in carbohydrates or fats?

 

43.  What is the chemical formula of valine?  C ______  H ______ O _______ N ______

 

44. What is the chemical formula of threonine?  C ______ H ______ O _____ N ______

 

45.  What is the chemical formula of glycine?  C ______  H ______ O _______ N _____

 

46. What is the chemical formula of alanine?  C ______ H ______ O _____ N ______

 

47. Are the chemical formulas for all amino acids the same?

 

48. How do the structural formulas for all the amino acids differ?

 

49. What end arrangement of atoms is present in amino acids that was also present in fatty acids?

 

Another end arrangement in al amino acids consists of a nitrogen atom and two hydrogen atoms. This group is called an amino group. 

 

50. Do the structural formulas for all of the amino acids have an amino group?

 

Protein is composed of many amino acids joined together chemically.  Cut out the six amino acids paper models. Cut along the solid lines only.  Attempt to join the molecules together like puzzle pieces.

 

 

51. Do the amino acids fit easily together to form a protein molecule?

 

In order to join the molecules, remove as many –OH ends and the –H ends as needed from each of the amino acid molecules.  Cut along the dotted lines.  Now attempt to join the six molecules together like puzzle pieces.   Use the following order:

 

                        gly- ala- gly- val- ala- thr

 

52. Do the amino acids now fit easily together to form a protein molecule?

 

53. What chemical substance is formed when the –OH and –H ends are joined?

 

54. How many water molecules are formed when six amino acids are joined?

 

55. What is the process called when you put together smaller molecules to form a larger molecule with the removal of water?

 

Tape or glue your protein molecule and the molecules of water to the blank sheet of paper.  Label them protein and water respectively.  Write the chemical formula water under its name.

 

QUESTIONS:

 

56. What three elements are present in all carbohydrates?

 

57. What molecules combine to form disaccharides?  Polysaccharides?

 

58. What is the ratio of hydrogen to oxygen in a carbohydrate?

 

59. Dehydration means “water loss”.  Synthesis means “ to put together”.  Explain why the chemical process responsible for building a carbohydrate, a fat or a protein is called dehydration synthesis?

 

60. What two types of molecules are needed to form a fat molecule?

 

61. What type of molecule is needed to form protein molecules?

 

62. How does a glycerol molecule differ from a carbohydrate molecule?

 

63. How do amino acid molecules differ from fatty acid molecules?

 

64. How are amino acid molecules the same are fatty acid molecules?

 

65. Hydro means “water” and lysis means “ to break apart”.  Hydrolysis is the process of breaking down a larger molecule into smaller molecules with the addition of water.  How many water molecules would it take to break down one molecule of fat into glycerol and the three fatty acids?