http://www.ck12.org Chapter 26. Biochemistry
FIGURE 26.16
A triglyceride is a lipid that is formed by
the esterification of glycerol with three
fatty acid molecules.Glycerol is a triol, an alcohol that contains three hydroxyl functional groups. A fatty acid is a long hydrocarbon
chain, generally from 12 to 24 carbons in length, with a carboxyl group on one end. Each of the three fatty acid
molecules undergoes an esterification reaction with one of the hydroxyl groups of the glycerol molecule. The result
is a large triester molecule referred to as a triglyceride (Figure26.16).
Triglycerides are used for long-term storage of energy in the human body. Because of the long carbon chains,
triglycerides are nearly nonpolar molecules, so they do not dissolve readily in polar solvents such as water. However,
oils and fats are soluble in nonpolar organic solvents, such as hexane or ethers.
Fats may be either saturated or unsaturated. Asaturated fatis a fat that consists of triglycerides whose carbon
chains consist entirely of carbon-carbon single bonds. Therefore, the carbon chains are saturated with the maximum
number of hydrogen atoms possible. Anunsaturated fatis a fat that consists of triglycerides whose carbon chains
contain one or more carbon-carbon double bonds. A fat with one double bond is called monounsaturated, while a
fat with multiple double bonds is called polyunsaturated (Figure26.17).
FIGURE 26.17
Saturated fats are derived from fatty acids
whose carbon chains contain all single
carbon-carbon bonds. A monounsatu-
rated fat contains one carbon-carbon dou-
ble bond, while a polyunsaturated fat con-
tains at least two double bonds.Unsaturated fats are generally considered to be healthier than saturated fats. One reason is that they contain fewer
calories than an equivalent amount of saturated fats. High consumption of saturated fats is linked to an increased
risk of cardiovascular disease. Some examples of foods with high concentrations of saturated fats include butter,
cheese, lard, and some fatty meats. Foods with higher concentrations of unsaturated fats include nuts, avocado, and
foods that contain various vegetable oils, such as canola oil and olive oil. The figure below (Figure26.18) shows
the percentages of different types of fat in some common foods.