1. Mechanical digestion: In the mouth, teeth break down the protein-containing food into smaller pieces, increasing the surface area for enzymes to work.
2. Chemical digestion:
- In the stomach: The acidic environment in the stomach triggers the release of pepsin, a protease enzyme that begins to break down proteins into smaller peptides.
- In the small intestine:
- The pancreas releases several digestive enzymes, including trypsin, chymotrypsin, and elastase, which further break down peptides into smaller oligopeptides and amino acids.
- The enzyme carboxypeptidase, produced by the pancreas, cleaves amino acids from the C-terminus (carboxyl end) of peptides.
3. Absorption:
- In the small intestine: The small intestine's inner lining contains tiny finger-like projections called villi, which increase the surface area for absorption.
- The oligopeptides and amino acids resulting from protein digestion are absorbed through the villi into the bloodstream.
- Some specialized enzymes called dipeptidases and tripeptidases on the intestinal brush border further break down any remaining oligopeptides into individual amino acids before absorption.
4. Metabolism: Once absorbed, amino acids are transported to the liver, where they can be used for various metabolic processes. They can be:
- Used to synthesize new proteins and other nitrogenous compounds.
- Converted into energy by being oxidized in the mitochondria.
- Converted into carbohydrates or fats through metabolic pathways.
Depending on the specific protein and the individual's digestive capabilities, some proteins may be more easily digestible than others. Factors like food preparation methods, cooking, and individual variations in enzyme production can influence protein digestion and absorption.
