Digestion of Protein by Proteases in the Digestive System

• Pepsin breaks down protein in the acidic conditions of the stomach:

Production of Pepsin

Pepsin is a protease enzyme that plays a crucial role in breaking down proteins in the stomach. It is secreted in an inactive form called pepsinogen by specialized cells known as chief cells in the gastric glands of the stomach lining.

The stomach’s acidic environment, maintained by hydrochloric acid (HCl) secreted by the parietal cells, activates pepsinogen into its active form, pepsin. The low pH (around pH 1.5-3.5) of the stomach denatures the pepsinogen, converting it into pepsin.

Action of Pepsin

Pepsin acts on proteins and breaks the peptide bonds that link the amino acids together. These peptide bonds are relatively stable in neutral or alkaline environments but are susceptible to the acidic conditions of the stomach.

Pepsin hydrolyzes the peptide bonds, resulting in the formation of smaller protein fragments called peptides. These peptides are still relatively large and complex compared to individual amino acids but are broken down enough to be more easily digestible.

• Trypsin breaks down protein in the alkaline conditions of the small intestine:

Production of Trypsin

Trypsin is another protease enzyme, but it is not produced and active in the stomach. Instead, it is produced in an inactive form called trypsinogen by the pancreas.

Trypsinogen is released into the small intestine along with other pancreatic juices when chyme (partially digested food) enters the duodenum, the first part of the small intestine.

To become active, trypsinogen needs to be converted into trypsin. This activation process is catalyzed by an enzyme called enteropeptidase, which is secreted by the cells lining the duodenum.

Action of Trypsin

Once activated into trypsin, it starts acting on the protein fragments that have been partially digested by pepsin in the stomach.

Trypsin continues to break down the peptides into even smaller peptide fragments. It specifically cleaves the peptide bonds next to the amino acids lysine and arginine, resulting in the formation of smaller peptide chains.

The smaller peptide fragments produced by trypsin are still too large to be efficiently absorbed by the body, so further digestion is necessary.