A very simple example of a digestion process is the hydrolysis of sucrose (common table sugar),
to produce glucose and fructose monosaccharides that can be absorbed through intestine walls to
undergo metabolism in the body. Each digestive hydrolysis reaction of carbohydrates has its own
enzyme. Sucrase enzyme carries out the reaction above, whereas amylase enzyme converts starch
to a disaccharide with two glucose molecules called maltose, and maltose in turn is hydrolyzed to
glucose by the action of maltase enzyme. A third important disaccharide is lactose or “milk sugar,”
each molecule of which is hydrolyzed by digestive processes to give a molecule of glucose and one of galactose.
Digestion can be a limiting factor in the ability of organisms to utilize saccharides. Many adults
lack the lactase enzyme required to hydrolyze lactose. When these individuals consume milk
products, the lactose remains undigested in the intestine, where it is acted upon by bacteria. These
bacteria produce gas and intestinal pain, and diarrhea may result. The lack of a digestive enzyme
for cellulose in humans and virtually all other animals means that these animals cannot metabolize
cellulose. The cellulosic plant material eaten by ruminant animals such as cattle is actually digested
by the action of enzymes produced by specialized rumen bacteria in the stomachs of such animals.
Stanley E. Manahan
Copyright © 2003 by CRC Press LLC
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