digestion of carbs, starches, and proteins

[student77]

Please explain the process of digestion of carbs, starches, and proteins including amylase and protease.  Thank you!

[Celeste]

Carbohydrate digestion begins in the mouth with salivary amylase. This enzyme catalyzes, or speeds along, the hydrolysis of the starch molecule. You may recall that hydrolysis is how nutrients that you eat are broken down, and it involves splitting bonds with water. Digestion of the carbohydrate does not resume until the food mass reaches the first part of the small intestine that we call the duodenum. Here the carbohydrate meets pancreatic amylase, which is similar to salivary amylase, and continues the breakdown of the carbohydrate.

Protein digestion begins in the stomach, where the acidic environment favors protein denaturation. Denatured proteins are more accessible as substrates for proteolysis than are native proteins. The primary proteolytic enzyme of the stomach is pepsin, a nonspecific protease that, remarkably, is maximally active at pH 2. Thus, pepsin can be active in the highly acidic environment of the stomach, even though other proteins undergo denaturation there.

Protein digestion is primarily a result of the activity of enzymes secreted by the pancreas. Aminopeptidases associated with the intestinal epithelium further digest proteins. The amino acids and di- and tripeptides are absorbed into the intestinal cells by specific transporters. Free amino acids are then released into the blood for use by other tissues.