The proteins subjected to digestion and  absorption are obtained from two sources.1.Exogenous2.Endogenous
The Fate of Dietary Protein The intake of dietary protein is in the range of  50-100g/day.Digestion and absorption .Main...
PROTEINS in the BODYAmino Acid Pool – amino acids that are available throughout the body (tissues and fluids) for use whe...
Protein DigestionWhole proteins are not absorbed.  Too large to pass through cell   membranes intact.   H3N+            ...
Protein Digestion  Initiated in stomach    HCl from parietal cells       StomachpH 1.6 to 3.2      Denatures 40, 30, a...
Protein Digestion – Small IntestinePancreatic enzymes secreted  Trypsinogen  Chymotrypsinogen  Procarboxypeptidase  P...
The release of pancreatic zymogens is mediated by the secreation of Cholecystokinin and secretin,two polypeptide hormones...
Digestion inSmall Intestine Zymogens must be converted to active form   Trypsinogen     Enteropeptidase/Trypsin Trypsin ...
Trypsin InhibitorsSmall proteins or peptidesPresent in plants, organs, and fluids  Soybeans, peas, beans, wheat  Pancr...
Protein Digestion   Proteins are broken down to     Tripeptides     Dipeptides     Free amino acids
Peptide Absorption Form in which the majority of  protein is absorbed More rapid than absorption of  free amino acids A...
Free Amino Acid Absorption Free amino acids   Carrier systems      Neutral AA      Basic AA               Na+   Na+   ...
Protein DigestionSmall intestine (brush border)  Aminopeptidases       Cleave at N-terminal AA  Dipeptidases       Cl...
In the Enterocytes… First cells that can use  the amino acids   Transport into portal    blood   Protein synthesis     ...
Basolateral MembraneTransport of free amino acids only*  Peptides are   hydrolyzed   within the   enterocyteTransport m...
Absorption of Intact Proteins   Newborns     First 24 hours after birth     Immunoglobulins        Passive   immunity ...
Abnormalities in the proteindigestion and amino acidabsorption.Defect in the pancreatic secreation.Cystic fibrosis,incomp...
HARTNUP’S DISEASEInability of itestinal and epithelial cells to  absorb neutral amino acids.Tryptophan  absorption is sev...
Digestion and absorption of proteins
Digestion and absorption of proteins
Digestion and absorption of proteins
Digestion and absorption of proteins
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Digestion and absorption of proteins

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Digestion and absorption of proteins

  1. 1. The proteins subjected to digestion and absorption are obtained from two sources.1.Exogenous2.Endogenous
  2. 2. The Fate of Dietary Protein The intake of dietary protein is in the range of 50-100g/day.Digestion and absorption .Maintenance of body protein stores.Net protein synthesis.Synthesis of non-protein compoundsOxidative deamination
  3. 3. PROTEINS in the BODYAmino Acid Pool – amino acids that are available throughout the body (tissues and fluids) for use when needed.Protein Turnover – of the ~ 300 grams of protein synthesized by the body each day, 200 grams are made from recycled amino acids.
  4. 4. Protein DigestionWhole proteins are not absorbed. Too large to pass through cell membranes intact. H3N+ H C C O H O R N C C HDigestive enzymes.Hydrolases R N H C C O H O– Break peptide bonds RSecreted as inactive pre-enzymes. Prevents self-digestion.
  5. 5. Protein Digestion Initiated in stomach HCl from parietal cells StomachpH 1.6 to 3.2 Denatures 40, 30, and 20 structures Pepsinogen from chief cells Pepsinogen HCl Pepsin Cleaves only when carbonyl group of the peptide bond is contributed by Aromatic amino acids. Protein leaves stomach as mix of insoluble protein, soluble protein, peptides and amino acids
  6. 6. Protein Digestion – Small IntestinePancreatic enzymes secreted Trypsinogen Chymotrypsinogen Procarboxypeptidase Proelastase Zymogens Collagenase
  7. 7. The release of pancreatic zymogens is mediated by the secreation of Cholecystokinin and secretin,two polypeptide hormones of digestive tract.
  8. 8. Digestion inSmall Intestine Zymogens must be converted to active form Trypsinogen Enteropeptidase/Trypsin Trypsin  Endopeptidase  Cleaves on carbonyl side of Lys & Arg Trypsin Chymotrypsinogen Chymotrypsin  Endopeptidase  Cleaves carboxy terminal Phe, Tyr and Trp Trypsin Procarboxypeptidase Carboxypeptidase  Exopeptidase  Removes carboxy terminal residues
  9. 9. Trypsin InhibitorsSmall proteins or peptidesPresent in plants, organs, and fluids Soybeans, peas, beans, wheat Pancreas, colostrumBlock digestion of specific proteinsInactivated by heat
  10. 10. Protein Digestion Proteins are broken down to Tripeptides Dipeptides Free amino acids
  11. 11. Peptide Absorption Form in which the majority of protein is absorbed More rapid than absorption of free amino acids Active transport  Energy required Metabolized into free amino acids in enterocyte Only free amino acids absorbed into blood
  12. 12. Free Amino Acid Absorption Free amino acids Carrier systems  Neutral AA  Basic AA Na+ Na+  Acidic AA  Imino acids Entrance of some AA is via active transport  Requires energy
  13. 13. Protein DigestionSmall intestine (brush border) Aminopeptidases  Cleave at N-terminal AA Dipeptidases  Cleave dipeptides into Aas. (Enterokinase or enteropeptidase)  Trypsinogen → trypsin  Trypsin then activates all the other enzymes
  14. 14. In the Enterocytes… First cells that can use the amino acids Transport into portal blood Protein synthesis Digestive enzymes Structure and growth Energy
  15. 15. Basolateral MembraneTransport of free amino acids only* Peptides are hydrolyzed within the enterocyteTransport mainly by diffusion and Groff & Gropper, 2000 Na-independent carriers *Whole proteins are nutritionally insignificant...
  16. 16. Absorption of Intact Proteins Newborns First 24 hours after birth Immunoglobulins  Passive immunity Adults Paracellular routes  Tight junctions between cells Intracellular routes  Endocytosis  Pinocytosis Of little nutritional significance... Affects health (allergies and passive immunity)
  17. 17. Abnormalities in the proteindigestion and amino acidabsorption.Defect in the pancreatic secreation.Cystic fibrosis,incomplete digestion of fat and protein,results in abnormal appearance of lipids (steatorrhea) and proteins in feces.Defective carrier system
  18. 18. HARTNUP’S DISEASEInability of itestinal and epithelial cells to absorb neutral amino acids.Tryptophan absorption is severely effected resulting in pellagra.CYSTINUREA.
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