What is the end product of protein digestion?

The end products of protein digestion are amino acids. Here's the quick journey:

1. Digestion starts in the stomach with pepsin breaking down large protein molecules into smaller polypeptides.
2. In the small intestine, enzymes from the pancreas (like trypsin and chymotrypsin) break these polypeptides down even further into tripeptides and dipeptides.
3. Finally, enzymes on the surface of the small intestine cells (brush border enzymes) break these down into single amino acids.

These individual amino acids are then absorbed through the intestinal wall into the bloodstream, where they are transported to cells throughout the body to build new proteins, enzymes, and tissues. So, while peptides are intermediate products, the final, absorbable units are always amino acids.