Lipids

Fats are complex molecules composed of long chains of carbon atoms (fatty acids) linked to a 3-carbon compound called glycerol. The structure of glycerol is quite simple, as shown in figure 4-21. As previously shown, organic acids each have a carboxyl group (-COOH) at the end of a chain of carbon atoms. A fatty acid is shown in figure 4-22.

Figure 4-21 Structural formula for glycerol.

HHHHHHH

HHHHHHH

Figure 4-22 Structural formula for a fatty acid.

When fatty acids react with glycerol to produce molecules of fat, a dehy-drolysis reaction takes place. Three molecules of water are removed (or created) for each molecule of fat manufactured, as shown in figure 4-23. As illustrated in the figure, the carbon atoms are linked to each other by single bonds, the remaining bonds being attached to hydrogen atoms. This is called

-3H20

OH H

OH H

OH H

HHHHHHHH

HHHHHHHH HHHHHHHHHH

HHHHHHHHHH H H H H H H H

H OHHHHHHHH

H — C —O—C—C—C—C—C— C—C—C—C—H

HHHHHHHH OHHHHHHHHHH

H —c—o—c—c—c—c—C—c—c —C—c—c—C—H HHHHHHHHHH OHHHHHHH H —C—O—C—C—C—C—C—C—C—C —H H HHHHHHH

Figure 4-23 A dehydrolysis reaction uniting glycerol and three fatty acid molecules to form a molecule of fat.

a saturated fat. An unsaturated fat has fewer hydrogen atoms and, hence, # Notes # some double bonds between adjacent carbon atoms, as shown in figure 4-24. An unsaturated fat can be changed to a saturated fat by hydrogénation, the process of adding hydrogen atoms to a compound.

H OHHHHHHHH H — C —O—C— C~C—C~ C—C—C—C—C

H H H H OH HHHHHHHHH H —C—O—C—C C C—C—C—C— C— C—C=C—C—H

H — C —O—C—C—C —C—C—C---C—C—C—H

Figure 4-24 Structural formula for an unsaturated fat.

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