SUMMARY

• 11.1 Fatty Acids Are a Main Source of Fuel

  Lipids are defined as water-insoluble molecules that are soluble in organic solvents. Fatty acids are an important lipid in biochemistry. Fatty acids are hydrocarbon chains of various lengths and degrees of unsaturation that terminate with a carboxylic acid group. The fatty acid chains in membranes usually contain between 14 and 24 carbon atoms; they may be saturated or unsaturated. Short chain length and unsaturation enhance the fluidity of fatty acids and their derivatives by lowering the melting temperature.

• 11.2 Triacylglycerols Are the Storage Form of Fatty Acids

  Fatty acids are stored as triacylglycerol molecules in adipose cells. Triacylglycerols are composed of three fatty acids esterified to a glycerol backbone. Triacylglycerols are stored in an anhydrous form.

• 11.3 There Are Three Common Types of Membrane Lipids

  The major classes of membrane lipids are phospholipids, glycolipids, and cholesterol. Phosphoglycerides, a type of phospholipid, consist of a glycerol backbone, two fatty acid chains, and a phosphorylated alcohol. Phosphatidylcholine, phosphatidylserine, and phosphatidylethanolamine are major phosphoglycerides. Sphingomyelin, a different type of phospholipid, contains a sphingosine backbone instead of glycerol. Glycolipids are sugar-containing lipids derived from sphingosine. Cholesterol, which modulates membrane fluidity, is constructed from a steroid nucleus. A common feature of these membrane lipids is that they are amphipathic molecules, having one hydrophobic and one hydrophilic end.