Pepsin trypsin and chymotrypsin are key digestion enzymes with proteolytic activity. Their role is to break amino acid bonds within the protein which organisms consume with food. As a result, amino acids which are key nutrients can be absorbed and used by organisms.
Pepsin was found to lyse proteins in the stomach. It degrades bonds which are formed by aromatic amino acids (tryptophan, tyrosine, and phenylalanine), leucine or methionine. However, it is not highly precise and can attack other types of bonds too. As its activity is highly dependent on pH and it stops working in the intestine, where pH is no longer acidic.
The completion of food digestion takes place in the small intestine. Here trypsin and chymotrypsin are active. Trypsin degrades bonds that are formed by carboxyl groups of basic amino acids such as lysine and arginine, while chymotrypsin degrades bonds that are formed by aromatic amino acids. As a result, proteins are digested into smaller peptides, which are easier to cleave.
The main function of pepsin, trypsin, and chymotrypsin is to cut proteins into smaller parts - peptides. After this carboxypeptidase and aminopeptidases can remove amino acids one by one from C-terminus and N-terminus respectively. Without this partial cleaving, it would have been taken an enormous amount of time to digest proteins that organisms consume with food.
Of course, these enzymes are tightly regulated and their enhanced activity can lead to diseases like ulcer and pancreatitis. However, the number of amino acids will dramatically decline with the loss of functions of these enzymes.