Chapter 3, Problem 3.14PS

QUANTITATIVE Thinking About Lipids. You should be able to answer each of the following questions based on the properties of lipids discussed in this chapter:

1. (a) How would you define a lipid? In what sense is the operational definition different from that of proteins, nucleic acids, or carbohydrates?
2. (b) Arrange the following lipids in order of decreasing polarity: cholesterol, estradiol, fatty acid, phosphatidyl choline, and triglyceride. Explain your reasoning.
3. (c) Which would you expect to resemble a sphingomyelin molecule more closely: a molecule of phosphatidylcholine containing two molecules of palmitic acid as its fatty acid side chains or a phosphatidylcholine molecule with one molecule of palmitate and one molecule of oleate as its fatty acid side chains? Explain your reasoning.
4. (d) Assume you and your lab partner Chris determined the melting temperature for each of the following fatty acids: arachidic, linoleic, linolenic, oleaic, palmitic, and stearic acids. Chris recorded the melting points of each but neglected to note the specific fatty acid to which each value belongs. Assign each of the following melting temperatures (in °C) to the appropriate fatty acid, and explain your reasoning: −11, 5, 16, 63, 70, and 76.5.
5. (e) For each of the following amphipathic molecules, indicate which part of the molecule is hydrophilic: phosphatidylserine, sphingomyelin, cholesterol, and triacylglycerol.