Final answer:
Protein breakdown begins in the stomach and is completed in the small intestine. The enzyme pepsin in the stomach breaks down proteins into smaller peptides, which are further broken down into amino acids in the small intestine.
Step-by-step explanation:
The digestion of proteins begins in the stomach and is completed in the small intestine. In the stomach, gastric juices are secreted which contain the enzyme pepsin. Pepsin breaks down proteins into smaller peptides. These peptides are then further broken down into individual amino acids by enzymes in the small intestine.