Where are brush border enzymes located and what is their general function?

• A. On the microvilli of enterocytes in the small intestine; complete final digestion of disaccharides and peptides into monosaccharides and amino acids.
• B. In the stomach; begin protein digestion.
• C. In the large intestine; digest cellulose.
• D. In the pancreas; digest proteins and fats.

Answer: (A)

Brush border enzymes are located on the microvilli of the enterocytes lining the small intestine, where they carry out the final steps of digestion as chyme passes by. They break disaccharides into monosaccharides (for example, sucrose into glucose and fructose, lactose into glucose and galactose, maltose into glucose) and hydrolyze small peptides into amino acids, making these products ready for absorption at the apical surface. This work happens right at the brush border, the cell membrane area exposed to the intestinal lumen. These enzymes aren’t active in the stomach, large intestine, or pancreas—the stomach digests proteins with acid and pepsin, the large intestine mainly handles water absorption and fermentation, and the pancreas releases other digestive enzymes into the lumen but not as part of the brush border itself.