1. Worked Example 23.1 Identifying Lipid Families
Use Figure 23.1 to identify the family of lipids to which each of these molecules belongs.
Analysis
Inspect the molecules and note their distinguishing characteristics. Molecule (a) has a four-member fused-ring system. Only sterols have this structure. Molecule (b) has three fatty acids esterified to a single backbone molecule—glycerol. Thus, (b) must be a member of the triacylglycerol family.
Solution
Molecule (a) is a sterol, and molecule (b) is a triacylglycerol.

2. Worked Example 23.2 Comparing Melting Points
Which of these two fatty acids has the higher melting point?
Analysis
First determine the chain length (number of carbon atoms) and the number of unsaturated bonds present. In general, the more carbon atoms present in a molecule, the higher the melting point. However, the higher the number of unsaturated bonds, the lower the melting point. The degree of unsaturation (defined as the number of double bonds) is more important than the number of carbon atoms when the number of carbon atoms is identical or similar.
Solution
Molecule (a) has 18 carbon atoms and two unsaturated bonds. Molecule (b) has 16 carbon atoms and one unsaturated bond. Although molecule (a) is slightly larger than molecule (b) and would be expected to have a higher melting point, molecule (a) has two double bonds, whereas molecule (b) has only one double bond. Since the degree of unsaturation is more important in these similarly sized molecules, molecule (b) has the higher melting point.

3. Worked Example 23.3 Identifying Complex Lipid Components
A class of membrane lipids known as plasmalogens has the general structure shown here. Identify the component parts of this lipid and choose the terms that apply to it: phospholipid, glycerophospholipid, sphingolipid, glycolipid. Is it most similar to a phosphatidylethanolamine, a phosphatidylcholine, a cerebroside, or a ganglioside?
Analysis

4. Worked Example 23.3 Identifying Complex Lipid Components
Continued
Solution
The terms that apply to this plasmalogen are phospholipids and glycerophospholipid. It has a structure nearly identical to phosphatidylethanolamine, so it is most similar to phosphatidylethanolamine.