Final answer:
Polypeptides are initially broken down by pepsin in the stomach, and digestion continues in the small intestine with pancreatic enzymes such as trypsin and chymotrypsin, and brush border enzymes like aminopeptidase and dipeptidase, resulting in amino acids absorbed by the bloodstream.
Step-by-step explanation:
Polypeptides are broken down by pepsin in the stomach and by pancreatic enzymes (trypsin, chymotrypsin, carboxypeptidase) and brush border enzymes (aminopeptidase, dipeptidase) in the small intestine.
The digestion of proteins begins in the stomach, where the enzyme pepsin, in combination with hydrochloric acid (HCl), starts breaking down proteins into smaller polypeptides. These polypeptides then move to the small intestine, where they encounter several pancreatic enzymes that the pancreas has secreted. These include trypsin and chymotrypsin, which are key to further breaking down the polypeptides by attacking specific bonds between amino acids. Additionally, another pancreatic enzyme called carboxypeptidase works at the free carboxyl end of the peptide chain to release free amino acids.
The small intestine's cells, specifically those of the brush border, produce other enzymes such as aminopeptidase and dipeptidase. These enzymes work from the opposite end of the polypeptide chain, facilitating the breakdown into individual amino acids ready for absorption into the bloodstream.