1. Sample Problem 17.1 Structures and Properties of Fatty Acids
Consider the line-angle structural formula for vaccenic acid, a fatty acid found in dairy products and human milk.
a. Why is this substance an acid?
b. How many carbon atoms are in vaccenic acid?
c. Is the fatty acid saturated, monounsaturated, or polyunsaturated?
d. Give the shorthand notation for the number of carbon atoms and double bonds in vaccenic acid.
e. Is it most likely to be solid or liquid at room temperature?
f. Would it be soluble in water?
Solution
a. Vaccenic acid contains a carboxylic acid group.
b. It contains 18 carbon atoms.
c. It is a monounsaturated fatty acid (MUFA).
d. 18:1
e. It is liquid at room temperature.
f. No. Its long hydrocarbon chain makes it insoluble in water.

2. Sample Problem 17.1 Structures and Properties of Fatty Acids
Continued
Study Check 17.1
Palmitoleic acid is a fatty acid with the following condensed structural formula:
a. How many carbon atoms are in palmitoleic acid?
b. Is the fatty acid saturated, monounsaturated, or polyunsaturated?
c. Give the shorthand notation for the number of carbon atoms and double bonds in palmitoleic acid.
d. Is it most likely to be solid or liquid at room temperature?
Answer
a. 16 b. monounsaturated c. 16:1 d. liquid

3. Sample Problem 17.2 Drawing the Structure for a Triacylglycerol
Draw the condensed structural formula for glyceryl tripalmitoleate (tripalmitolein), which is used in cosmetic creams and lotions.
Solution
Glyceryl tripalmitoleate (tripalmitolein) is the triacylglycerol that contains ester bonds between glycerol and three palmitoleic acid molecules.
Step 1 Draw the condensed structural formulas for glycerol and the fatty acids.

4. Sample Problem 17.2 Drawing the Structure for a Triacylglycerol
Continued
Step 2 Form ester bonds between the hydroxyl groups on glycerol and the carboxyl groups on each fatty acid.
Study Check 17.2
Draw the condensed structural formula for the triacylglycerol containing three molecules of myristic acid (14:0).
Answer

5. Sample Problem 17.3 Reactions of Lipids During Digestion
Write the equation for the reaction catalyzed by the enzyme lipase that hydrolyzes glyceryl trilaurate (trilaurin) during the digestion process.
Solution
glyceryl trilaurate is an ester of glycerol and three lauric acid molecules (12:0). When the ester undergoes hydrolysis by lipase, the products are glycerol and three lauric acid molecules.

6. Sample Problem 17.3 Reactions of Lipids During Digestion
Continued
Study Check 17.3
What is the name of the product formed when a triacylglycerol containing oleic acid (8:1) and linoleic acid (18:2) is completely hydrogenated?
Answer
glyceryl tristearate (tristearin)

7. Sample Problem 17.4 Drawing Glycerophospholipid Structures
Draw the condensed structural formula for the cephalin that contains two stearic acids, phosphate, and serine as the ionized amino alcohol.
Solution

8. Sample Problem 17.4 Drawing Glycerophospholipid Structures
Continued
Study Check 17.4
Draw the condensed structural formula for the lecithin that contains two myristic acids phosphate, and choline as the ionized amino alcohol.
Answer

9. Sample Problem 17.5 Sphingomyelin
The sphingomyelin found in eggs contains sphingosine, palmitic acid, the 16-carbon saturated fatty acid, and the ionized amino alcohol choline. Draw the condensed structural formula for this sphingomyelin.
Solution

10. Sample Problem 17.5 Sphingomyelin
Continued
Study Check 17.5
Stearic acid is found in sphingomyelin in the brain. Draw the condensed structural formula for this sphingomyelin using ethanolamine as the ionized amino alcohol.
Answer

11. Sample Problem 17.6 Cholesterol
Refer to the structure of cholesterol for each of the following questions:
a. What part of cholesterol is the steroid nucleus?
b. What features have been added to the steroid nucleus in cholesterol?
c. What classifies cholesterol as a sterol?
Solution
a. The four fused rings form the steroid nucleus.
b. The cholesterol molecule contains a hydroxyl group (—OH) on the first ring, one double bond in the second ring, methyl groups (—CH3) at carbons 10 and 13, and a branched carbon chain.
c. The hydroxyl group determines the sterol classification.
Study Check 17.6
Why is cholesterol in the lipid family?
Answer
Cholesterol is not soluble in water; it is classified with the lipid family.

12. Sample Problem 17.7 Lipid Bilayer in Cell Membranes
Describe the role of phospholipids in the lipid bilayer.
Solution
Phospholipids consist of polar and nonpolar parts. In a cell membrane, an alignment of the nonpolar sections toward the center with the polar sections on the outside produces a barrier that prevents the contents of a cell from mixing with the fluids on the outside of the cell.
Study Check 17.7
What is the function of cholesterol in the cell membrane?
Answer
Cholesterol adds strength and rigidity to the cell membrane.