Carbohydrate reactions are indicated by blue reaction arrows. The enzymes involved are in italics and label the relevant reaction arrows. Membrane-bound enzymes are written along the inner surface of the GI tract.
Carbohydrates are composed of chains of simple sugars. The term polysaccharide refers to the largest molecules, oligosaccharides contain from 3 to 10 sugars, disaccharides are double sugars, and monosaccharides are simple sugars.
In the mouth, amylase in saliva breaks polysaccharides into oligosaccharides. No carbohydrate digestion occurs in the stomach. In the small intestine, polysaccharides that survived digestion in the mouth are broken down to oligosaccharides by pancreatic amylase.
The remaining enzymes involved in carbohydrate digestion are membrane bound. Dextrinase breaks oligosaccharides into the disaccharides sucrose, maltose, and lactose. Next, disaccharidases--sucrase, maltase, lactase--break the corresponding disaccharides into monosaccharides that are absorbed into the blood stream.
Blue arrows point from each disaccharide to their corresponding monosaccharides. Sucrose yields a molecule of glucose and a molecule of fructose. Maltose yields two molecules of glucose. Lactose yields one glucose and one galactose.
Last Updated: 17/19/2005