Final answer:
Pepsin primarily breaks down proteins into peptides in the stomach. Complete digestion to amino acids occurs in the small intestine with the help of other enzymes.
Step-by-step explanation:
If pepsin were digesting an actual protein substrate, the product would be peptides and potentially also some amino acids. However, the predominating products created by pepsin are peptides, which are short chains of four to nine amino acids. These peptides are further broken down into single amino acids by additional enzymes like carboxypeptidase, dipeptidase, and aminopeptidase in the small intestine.
Pepsin is a proteolytic enzyme secreted in the stomach that specifically acts on peptide bonds, especially those contributed by aromatic amino acids like tyrosine, tryptophan, and phenylalanine. While protein digestion initiates with the action of pepsin in the stomach, the complete hydrolysis of proteins into free amino acids, suitable for absorption into the bloodstream, occurs mostly in the small intestine with the aid of pancreatic enzymes like trypsin, elastase, and chymotrypsin, followed by various peptidases.