Write the main function of pepsin.

The main function of pepsin is to aid in the digestion of proteins in the stomach. Pepsin is an enzyme that belongs to the class of proteases, which are enzymes that break down proteins into smaller peptide fragments. It is produced and secreted by the chief cells of the stomach lining in an inactive form called pepsinogen.

When food is ingested, the acidic environment of the stomach activates pepsinogen to its active form, pepsin. This activation occurs due to the low pH (high acidity) of the stomach, which is primarily maintained by hydrochloric acid secreted by parietal cells. The acidic environment causes pepsinogen to undergo a conformational change that converts it into pepsin. Once activated, pepsin starts breaking down the peptide bonds that hold the amino acids together in proteins, ultimately reducing them into smaller peptides and amino acids.

The partially digested mixture of food, hydrochloric acid, and pepsin is known as chyme. The breakdown of proteins into smaller fragments by pepsin is a crucial step in the digestion process. These smaller peptides and amino acids can be further digested and absorbed in the small intestine, where other enzymes like trypsin and chymotrypsin continue the process of protein digestion.

In summary, the main function of pepsin is to initiate the digestion of dietary proteins in the stomach by breaking them down into smaller peptide fragments, which can be further processed and absorbed in the small intestine.