Final answer:
The complete digestion of proteins into amino acids is carried out by proteases produced in the small intestine, following initial breakdown by pepsin in the stomach.
Step-by-step explanation:
Protein Digestion and Enzyme Action
In the context of protein digestion, the breakdown of proteins into amino acid constituents is completed by proteases produced in the small intestine. Digestion begins in the stomach, where hydrochloric acid (HCl) denatures proteins and an enzyme called pepsin begins to break them down into smaller polypeptides. As digestion continues in the small intestine, pancreatic enzymes like trypsin and chymotrypsin, as well as peptidases from the intestinal lining, further reduce these polypeptides into individual amino acids, which are then absorbed into the bloodstream. Thus, the correct answer to the question is 'c. proteases produced in the small intestine'.