How does pepsin function in protein digestion?

Pepsin functions in protein digestion by breaking down proteins into smaller peptides in the stomach.

Pepsin is a type of protease, an enzyme that breaks down proteins. It is produced in the stomach by the chief cells in the form of pepsinogen, an inactive precursor. When pepsinogen comes into contact with the acidic environment of the stomach, it is converted into its active form, pepsin. This process is known as an autocatalytic activation.

The primary role of pepsin in protein digestion is to cleave proteins into smaller peptides. It does this by breaking the peptide bonds between the amino acids that make up proteins. Pepsin is particularly effective at cleaving bonds involving the aromatic amino acids phenylalanine, tryptophan, and tyrosine. This initial breakdown of proteins is crucial as it allows the enzymes in the small intestine to further digest the peptides into individual amino acids, which can then be absorbed into the bloodstream.

Pepsin functions optimally at a pH of around 1.5 to 2, which is the typical pH of the stomach. This acidic environment not only activates pepsinogen into pepsin but also helps to denature dietary proteins, making them more accessible to enzymatic digestion. If the pH of the stomach rises above 5, pepsin becomes denatured and loses its enzymatic activity.

In summary, pepsin plays a crucial role in the initial stages of protein digestion in the stomach. It is produced as an inactive precursor, pepsinogen, which is activated by the acidic environment of the stomach. Once activated, pepsin breaks down proteins into smaller peptides by cleaving peptide bonds, particularly those involving aromatic amino acids. This process prepares the proteins for further digestion and absorption in the small intestine.