Answer to Question 1
The phospholipids (together with sterols), make up only 5 percent of the lipids in the diet, but they are nevertheless worthy of attention. Among the phospholipids, the lecithins are of particular interest. Like the triglycerides, the lecithins and other phospholipids have a backbone of glycerol; they differ from the triglycerides in having only two fatty acids attached to the glycerol. In place of the third fatty acid, they have a phosphate group (a phosphorus-containing acid) and a molecule of choline or a similar compound. The fatty acids make the phospholipids soluble in fat; the phosphate group enables them to dissolve in water. Such versatility benefits the food industry, which uses phospholipids as emulsifiers to mix fats with water in such products as mayonnaise and candy bars. In addition to the phospholipids used by the food industry as emulsifiers, phospholipids are also found naturally in foods. The richest food sources of lecithin are eggs, liver, soybeans, wheat germ, and peanuts. Lecithins and other phospholipids are important constituents of cell membranes. They also act as emulsifiers in the body, helping to keep other fats in solution in the watery blood and body fluids. In addition, some phospholipids generate signals inside the cells in response to hormones, such as insulin, to help alter body conditions.
Answer to Question 2
c
Hydrolysis reactions for some biochemically important phosphate compounds (part 2)
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