Protein, Lipid and Carbohydrate Digestion - Essay Example

To understand the process of digestion better, we shall look at the process for each type of food - proteins, lipids or fats, and carbohydrates.Chemical digestion of proteins starts in the stomach. The stomach produces HCl which converts pepsinogen to pepsin. Pepsin is a kind of endopeptidase which splits the internal peptide bonds in the protein molecules. That is, it breaks the primary structure of the protein. As opposed to endopeptidases, exopeptidases split the first or last peptide bond in the polypeptide.

Zymogens, a form of protease, are secreted by the pancreas, which in turn are activated by enteropeptidase. Enteropeptidases convert trypsinogen to trypsin, which then hastens the conversion of more trypsinogen to trypsin. Furthermore, other zymogens are converted by trypsin into their active forms. Carboxypeptidase is converted from procarboxypeptidase. Chymotrypsin is converted from chymotrypsinogen. Both trypsin and chymotrypsin are endopeptidases. Carboxypeptidase, on the other hand, is an exopeptidase.

Protein digestion is a concerted effort of all these enzymes.Lipid or fat digestion occurs only in the small intestine. As a result, most fat/lipid molecules remain undigested when they reach the duodenum. Bile, which is produced by the liver and stored gall bladder, emulsifies fat molecules into smaller molecules. Then they are hydrolyzed into fatty acids and glycerol by the pancreatic lipase and are then absorbed in the intestine.Carbohydrate digestion begins in the mouth with the breaking up of starch and glycogen into smaller oligosaccharides, maltotriose, and maltose.

Disaccharidases attached to the epithelium of the duodenum are enzymes that split disaccharides into monosaccharides. Each disaccharidase is specific to a particular disaccharide. For instance, maltase hydrolyzes maltose. Monosaccharides are then absorbed in the area where the final breakdown occurred.Digestion is a very complex biological process that seeks our appreciation. Indeed, it is such a wonder how this complexity arose from chaos.