Download Lipids - U of L Class Index

Chapter 18
18
Lipids
Study Goals
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Describe the properties and types of lipids.
Write the structures of triacylglycerols obtained from glycerol and fatty acids.
Draw the structure of the product from hydrogenation, hydrolysis, and saponification of
triacylglycerols.
Distinguish between phospholipids, glycolipids, and sphingolipids.
Describe steroids and their role in bile salts, vitamins, and hormones.
Describe the lipid bilayer in a cell.
Chapter Outline
18.1
18.2
18.3
18.4
18.5
18.6
18.7
18.8
Lipids
Explore Your World: Solubility of Fats and Oils
Fatty Acids
Health Note: Omega-3 Fatty Acids in Fish Oils
Waxes, Fats, and Oils
Explore Your World: Fats and Oils
Chemical Properties of Triacylglycerols
Health Note Olestra: A Fat Substitute
Environmental Note: Trans Fatty Acids and Hydrogenation
Explore Your World: Types of Fats
Glycerophospholipids
Sphingolipids
Health Note: Lipid Diseases
Steroids: Cholesterol, Bile Salts, and Steroid Hormones
Health Note: Anabolic Steroids
Plasma (Cell) Membranes
Chapter Summary and Demonstrations
1. Types of Lipids
Lipids are discussed in terms of their components and solubility in various solvents. Saturated and
unsaturated fatty acids are described along with a comparison of their melting points.
Demonstration: I introduce this chapter with examples of lipids such as margarine, butter, lard,
cooking oils (corn, olive, safflower), gallstones, and vitamin A and oil of lemon.
Demonstration: Read the labels on some vegetable oils, margarines, or peanut butter. Ask students
what they know about saturated fat, unsaturated fats, and polyunsaturated fats. What process
occurred if the label states that the product is partially hydrogenated?
2. Fatty Acids and Triglycerides
The formation of the ester linkage between alcohols and fatty acids in waxes or glycerol and fatty
acids in triglycerides is shown. Several reactions of the triglycerides including hydrogenation, acid
and enzyme hydrolysis, saponification and oxidation are described.
Lipids
Demonstration: A discussion of hydrogenation of vegetable oils in the production of margarine is
an eye opener for many students. I place bottles of oil on the table along with a tub and cube of
margarine, and perhaps some Crisco. I ask the students how the oils in the bottles become the solid
products in front of them. This leads into a practical discussion of hydrogenation and the terms
associated with lipids such as unsaturated and saturated fats.
3. Phospholipids
The phospholipids are discussed along with their dual polarity and function in cell membranes.
Students are asked to look at the difference in properties for each of the components in cell
membranes. The chapter concludes with the coverage of steroids and steroid hormones with a
discussion of high- and low-density lipoproteins.
Demonstration: Bring in samples of lecithin, a phospholipid, and perhaps some cholesterol (if you
have gallstones). A discussion of anabolic steroids (see health note) is interesting to students who
are athletes or lift weights.
Laboratory Suggestions
Lab 30 Lipids
Students observe the physical and chemical properties of some common lipids and draw the
structure of a typical triacylglycerol. Chemical tests are used to distinguish between saturated and
unsaturated fats. A sample of hand lotion is prepared, which illustrates the physical properties of
various types of lipids.
A. Triacylglycerols
B. Physical Properties of Some Lipids and Fatty Acids
C. Bromine Test for Unsaturation
D. Preparation of Hand Lotion
Laboratory Skills to Demonstrate
Remind students of the change in color with bromine adds to a double bond.
Lab 31 Glycerophospholipids and Steroids
Students isolate cholesterol and lecithin from egg yolk using extraction techniques. The differences
in solubility of cholesterol and lecithin in acetone and ether is used to separate the steroid from the
glycerophospholipid.
A. Isolating Cholesterol in Egg Yolk
B. Isolating Lecithin in Egg Yolk
Laboratory Skills to Demonstrate
Caution in use of flammable solvents
Proper disposal techniques for organic compounds
Lab 32 Saponification and Soaps
Soap is prepared by the saponification of a triglyceride and collected. The behavior of soap with soft
water, oil and CaCl2 is observed.
A. Saponification: Preparation of Soap
B Properties of Soap and Detergents
Laboratory Skills to Demonstrate
Caution in the saponification procedure using NaOH to form soap.
Use of the Büchner filtration apparatus.