Concept:Protein digestion is a gradual enzymatic process occurring mainly in the stomach and small intestine, utilizing endopeptidases and exopeptidases.
Formula:$$ \text{Protein} \xrightarrow{\text{Proteases}} \text{Small Peptides} + \text{Amino Acids} $$
Solution:- By the time dietary proteins reach the brush border of the small intestine for absorption, pancreatic and gastric proteases have aggressively cleaved them.
- However, they are not strictly reduced to single amino acids; rather, the intestinal lumen contains a mixture of free amino acids and small polypeptides (dipeptides and tripeptides).
- These di- and tripeptides are absorbed by enterocytes alongside free amino acids.
Why other options are incorrect:Digestion does not perfectly yield 'only' amino acids in the lumen before absorption. Conversely, saying it is 'only' polypeptides ignores the massive amount of free amino acids produced. Ammonia is a metabolic waste product of deamination in the liver, not a product of digestive tract hydrolysis.
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