Action of Digestive Enzymes
Mechanical processes of cutting and grinding by teeth and muscular mixing by the intestinal tract are important in digestion. However, reduction of foods to small, absorbable units relies principally on chemical breakdown by enzymes, discussed in Cellular Metabolism . Digestive enzymes are hydrolytic enzymes, or hydrolases, so called because food molecules are split by the process of hydrolysis, breaking of a chemical bond by adding the components of water across it:
In this general enzymatic reaction, R −R represents a food molecule that is split into two products, R −OH and R −H. Usually these reaction products must in turn be split repeatedly before the original molecule is reduced to its numerous subunits. Proteins, for example, are composed of hundreds, or even thousands, of interlinked amino acids, which must be completely separated before the individual amino acids can be absorbed. Similarly, carbohydrates must be reduced to simple sugars. Fats (lipids) are reduced to molecules of glycerol, fatty acids, and monoglycerides, although some fats, unlike proteins and carbohydrates, may be absorbed without first being completely hydrolyzed. There are specific enzymes for each class of organic compounds. These enzymes are located in specific regions of the alimentary canal in an “enzyme chain,” in which one enzyme may complete what another has started. The product then moves posteriorly for still further hydrolysis.
In this general enzymatic reaction, R −R represents a food molecule that is split into two products, R −OH and R −H. Usually these reaction products must in turn be split repeatedly before the original molecule is reduced to its numerous subunits. Proteins, for example, are composed of hundreds, or even thousands, of interlinked amino acids, which must be completely separated before the individual amino acids can be absorbed. Similarly, carbohydrates must be reduced to simple sugars. Fats (lipids) are reduced to molecules of glycerol, fatty acids, and monoglycerides, although some fats, unlike proteins and carbohydrates, may be absorbed without first being completely hydrolyzed. There are specific enzymes for each class of organic compounds. These enzymes are located in specific regions of the alimentary canal in an “enzyme chain,” in which one enzyme may complete what another has started. The product then moves posteriorly for still further hydrolysis.
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