How are proteins broken down during digestion?

Proteins are broken down during digestion through the process of enzymatic hydrolysis, primarily by pepsin and trypsin.

In the human digestive system, the breakdown of proteins begins in the stomach. Here, the gastric glands secrete hydrochloric acid which denatures the proteins, unravelling them and making them more accessible to enzymatic action. The chief cells in the stomach lining produce an enzyme called pepsinogen, which is an inactive form of pepsin. The acidic environment in the stomach activates pepsinogen into pepsin, which starts the process of protein digestion by breaking down the proteins into smaller polypeptides.

The partially digested proteins then move into the small intestine, where the pancreas releases another enzyme called trypsin. Trypsin continues the breakdown of proteins into even smaller peptides. Other enzymes, such as carboxypeptidase and aminopeptidase, also secreted by the pancreas, further break down these peptides into individual amino acids.

These amino acids are then absorbed through the small intestine's lining into the bloodstream, where they can be transported to cells throughout the body. The cells can then use these amino acids to synthesise new proteins as needed.

It's important to note that the process of protein digestion is a complex one, involving a range of enzymes and different stages of breakdown. Each enzyme has a specific role and acts on a specific type of bond within the protein molecule. This specificity is due to the unique shape and structure of each enzyme, which allows it to bind to its specific substrate and catalyse the reaction. This is a key concept in understanding how proteins are broken down during digestion.