Name______Date______class_____

Molecules of Life: Lipids

Biologists nowadays depend upon chemists for much of their understanding of life and the life processes. Therefore, an understanding of some chemical concepts important to living things is necessary.

Carbohydrates, fats, proteins and nucleic acids are the four major groups of organic molecules found in living organisms.

The lipids are the fats, oils, and waxes. Like carbohydrates, fats contain carbon, hydrogen, and oxygen, but the proportion of energy when combined with oxygen is greater.

With this lab exercise you will be expected to: 1) Understand the structures of alcohols and fatty acids; 2) Construct molecular models of fat; 3) Be able to distinguish between models and actual chemical formulas of molecules; and 4) Be able to determine the molecular characteristics of fats.

Procedure:

Students should work independently or in teams as directed by their instructor. It will be necessary for each student to complete his own worksheet while possibly sharing a packet of molecular parts with other students. The packet of molecular parts consists of:

15Carbon (C) –tetrahedral electrons – black32 Hydrogen (H) – single electron – white

5 Oxygen (O) – double electrons – blue51 Electron bond – plastic tube – white

  1. FATS

On a molecular basis, all fats are somewhat similar. Just as carbohydrates are composed of smaller molecules called monosaccharides, all fats are composed of smaller molecules. The smaller molecules in fats are glycerol (an alcohol) and fatty acids.

  1. Alcoholsare organic compounds that have the hydroxide (-OH) radical. Two examples of common alcohols are shown in Fig. 1.

B. Glycerol is an alcohol with three hydroxide groups as shown in Fig. 2.

FIG. 1 Two common alcohols: Methyl alcohol and Ethyl alcohol FIG. 2. Glycerol.

1. What elements are present in glycerol?______

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

3. What is the molecular formula for methyl alcohol?______

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

Build a model of each molecule (Methyl & Ethyl Alcohol & Glycerol. Have different classmates inspect your models and print their full name here for each.

Methyl Alcohol / Ethyl Alcohol / Glycerol

C. Fatty Acids

The second molecule which contributes to forming fat is a long molecule called a fatty acid. Many different fatty acids exist, but all are similar in several ways.

  1. The structural formulas of three fatty acids are shown in Fig. 3.

Fig. 3 Structural formulas of Butyric acid, Caproic acid, and Lauric acid.

  1. Construct the Lauric acid model of a fatty acid. Show your instructor: ______

This constructed model represents the three-dimensional shape of the molecule. The 3 illustrate above show that individual molecules of fatty acids do differ from one another in the R group (a long hydrocarbon chain) and that they all contain a carboxyl group (-COOH). Therefore, a general formula for organic acids is R-COOH.

  1. Examine the structural formulas of the three fatty acids.
  2. What elements are present in all fatty acids?______
  3. What is the molecular formula of Butyric acids?______

Caproic acid?______Lauric acid?______

  1. Does a 2 to 1 ratio of hydrogen atoms to oxygen atoms exist in fatty acids?______
  2. Is the ratio of hydrogen atoms to oxygen atoms the same in each fatty acid?______

Give specific examples of the ratios for each acid. Butyric acid?______

Caproic acid?______Lauric acid?______

  1. Note that the carboxyl group is found in all three fatty acids.

D.Forming Fats

A fat molecule consists of one glycerol molecule and three fatty acid molecules joined together.

  1. With two other groups, attempt to join together the glycerol molecule with three fatty acids. Will the fat molecule stay together?______
  2. It will be necessary to remove three –OH ends from the glycerol molecule and the –H end from each of the fatty acids carboxyl end in order to join molecules. Does this enable the molecules to be joined together?______If so, do so.
  3. Join the –H and –OH ends. What chemical substance is found when the –H and –OH ends are joined?______
  4. Production of a fat molecule is a chemical reaction. A chemical shorthand way of expressing the formation of a fat is as follows: Fatty acids+ Glycerol ---Fat + Water
  5. How many water molecules are formed when one fat molecule is produced?______

14. Many fats exist in living things. The wide variety of fats is formed by different combinations of fatty acid molecules.

Take your fat and any other parts to have your instructor stamp or sign off that you have constructed a Fat molecule:

______.

15. Identify the different parts of your fat molecule (4 total) ______

Interpretations:

1. Dehydration means “water loss.” Synthesis means “to put together.” Explain why the chemical process responsible for building a fat or protein molecule is called dehydration synthesis.______

2. How would hydrolysis affect your fat? Explain ______

3. How does a glycerol molecule differ from a carbohydrate molecule? (Use structural formulas for comparison.)______

4. How does a fatty acid molecule differ from a carbohydrate molecule?______