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Protein Digestion

Protein Digestion

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Major Components of Protein Digestion
Denaturation
  • Protein unfolding (uncoiling), which occurs in the highly acidic gastric milieu, where the pH is ~ 2.
Peptide bond cleavage (commonly referred to as digestion)
  • Enzymatic activity of proteases (peptidases), which catalyze hydrolytic peptide bond cleavage, most prominently by pancreatic enzymes within the proximal small intestine, where the pH is ~ 6.
Peptide Uptake
  • Uptake of short peptides into enterocytes (brush border cells along the small intestine), where they are further cleaved into individual amino acids.
Amino Acid Absorption
  • The diffusion and transport of amino acids out of enterocytes and into the surrounding capillaries for systemic dispersion.
Protein Digestion: Diagram
  • In Western nations, we consume ~ 100 grams/day of dietary protein (70 to 100 grams/day).
– We see that protein is in its coiled (folded) state.
  • Another ~ 100 grams/day of protein (35 to 200 grams/day) enters the gut endogenously.
– These are the nitrogen-containing materials that pass into the gut: the digestive enzymes, desquamated cells, bile salts, phospholipids, lysed cells, plasma proteins, etc…).
  • We use the laboratory value of fecal nitrogen excretion to measure protein absorption efficiency.
– Poor protein digestion and absorption means that proteins pass through our GI system and into our fecal waste, unabsorbed.

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