Digestion And Absorption Of Proteins Flashcards
Protein digestion
Catabolic pathway
-Proteins are large polypeptides made up of Amino acids (AAs)
-AAs binds together by peptide bond
-The bond that is broken during digestion of Proteins
are called peptide bond
Protein digestion in the stomach: production of pepsin
-Chief cells → pepsinogen → activate → Pepsin
-Activation of Pepsinogen to pepsin requires an acidic environment
-Parietal cells → HCL → Decrease the pH → Acidic Environment 1.8-3.5 → stimulate the conversion of pepsinogen into pepsin
-↑pH → pepsin inactivated
Protein digestion in the stomach: function of pepsin
-Pepsin stimulates the conversion of pepsinogen into pepsin (=Auto activator)
-Pepsin converts large polypeptide → smaller polypeptides
-Targets aromatic amino acids → Break bonds on carboxyl side
-Tyrosine
-Phenylalanine
-Tryptophan
Source of bicarbonate
Mucosal cells
Function of bicarbonate
Neutralizes gastric acids
Bicarbonate stimulate by
Secretin
Source of CCK
I cells (duodenum, jejunum)
Functions of CCK
⬆️Contraction of the gallbladder
↑ Secretion of pancreatic Enzymes
↑Relaxation of the sphincter of Oddi
CCK stimulated by
Postprandial: fatty acids and amino acids entering the small intestine
Source of secretin
S cells (duodenum)
Functions of secretin
↑Pancreatic secretion of bicarbonate
↑Secretion of bile
Secretin stimulated by
Postprandial: ↑ gastric acid and fatty acids in the duodenum
Source of GIP
K cells (Duodenum, jejunum)
Functions of GIP
↑ Insulin secretion
↓ Secretion of gastric acid
GIP stimulated by
Postprandial: fatty acids, glucose, amino acids entering small intestine
GIP
“Glucose-dependent insulinotropic peptide”
“Gastric inhibitory polypeptide”
Production of pancreatic processes
-CCK= Cholecystokinin
-Stimulate acinar cells to produce Proteases
-Relaxes the Sphincter of Oddi → ejection of the Proteases to the duodenum
-Proenzymes (Inactive)
-Trypsinogen
-Chymotrypsinogen
-Procarboxypeptidase
-Proelastase
Activation of pancreatic proteases
-Enterokinase in the epithelial cells of the lumen → brush border enzyme → activate trypsinogen → trypsin
-Trypsin stimulates the activation of proenzymes
1) Trypsinogen → trypsin
2) Chymotrypsinogen → chymotrypsin
3) Procarboxypeptidase → carboxypeptidase (A&B)
4) Proelastase → elastase
Function of pancreatic proteases: trypsin
-Small polypeptide → Cleave peptide bonds on the
carboxyl side where there are Lysine and Arginine → tripeptide, dipeptide
-Exception they cannot hydrolyze the bond if there is Proline next to Lysine or Arginine
Function of pancreatic proteases: chymotrypsin
Small polypeptide→ same as pepsin → Cleave peptide bonds on the carboxyl side where there are Tyrosine, Phenylalanine, Tryptophan → tripeptide, dipeptide
Function of pancreatic proteases: carboxypeptidase
Small polypeptide→ act on carboxyl end→ AA, dipeptide, tripeptide
Function of pancreatic proteases: elastase
Small polypeptide→ act on carboxyl end → AA, dipeptide, tripeptide
Brush border enzymes of small intestin
Dipeptidase
Aminopeptidase
Location of brush border enzymes
-Enterocytes→ epithelial cell found in the small intestine
-Most of the absorption occurs in the small intestine
-Structural Modifications that increase surface area in the small intestine →↑Digestion and ↑Absorption
-Circular Folds
- Villi
-Microvilli
-Enterocyte → little cytoplasmic extensions → increase the surface area for chemical digestion and absorption → microvilli → high concentration of brush border enzymes
Absorption of protein: apical membrane: transporters
-AA Transporters
-Dipeptide Transporters
-Tripeptide Transporters
-Na+ /H+ Antiporter
Absorption of proteins: apical membrane: dipeptides and tripeptides uptake mechanism
-Dipeptide Transporters = H+ / Dipeptide cotransporter
-Tripeptide Transporters= H+ / Tripeptide cotransporter
-Dipeptide and tripeptide uptake is an active process driven by a proton gradient.
-Na+ /H+ Antiporter → brings in proton in exchange of Na+
-Proton used for the transportation of the Dipeptide and tripeptide→ Symport mechanism
Absorption of proteins: apical membrane: AAs Uptake Mechanism
-AA Transporters = Na+ / AA cotransporter
-Na+/K+ / ATPase →↓Na+ in the enterocyte
-Na+/K+ ATPase on the basal membrane → pump 3 Na+ outand2K+ in+utilizinganATP→↓Na+ →Na+ in lumen»_space; Na+ in the enterocyte → AAs follow Na+ from lumen to enterocyte
-Secondary active transport → Driving Force is sodium concentration gradient
-Sodium moves down its concentration gradient into the cell, taking AA
-AA move against its concentration gradient
Absorption of proteins: enterocyte
Enzyme in the enterocyte → Intracellular Peptidase cleave dipeptide, tripeptide → AAs
Absorption of proteins: basolateral membrane
-Transporter: AA transporters
-Mechanism:
-AAs move out of the cell through Facilitated diffusion mechanism → capillaries → veins → hepatic portal vein → liver
-In the liver the AAs → Protein Synthesis
-↑ Insulin release in the fed state → Enhance protein
synthesis and AAs Uptake
Pepsinogen
Activating agent: enteropeptidase and trypsin
Active enzyme: pepsin
Location: stomach
Function: cleaves bonds involving Phenylalanine, Tyrosine, and Tryptophan
Product: peptides, oligopeptides
Trypsinogen
Activating agent: enteropeptidase and trypsin
Active agent: trypsin
Location: pancreas secretion to Duodenum
Function: cleaves bonds of the C-terminal of Lysine and Arginine
Product: tripeptide, dipeptide
Chymotrypsinogen
Activating agent: trypsin
Active enzymes: chymotrypsin
Location: pancreas secretion to Duodenum
Function: cleaves bonds involving Phenylalanine, Tyrosine, and Tryptophan
Product: tripeptide, dipeptide
Pro-elastase
Activating agent: trypsin
Active enzyme: elastase
Location: pancreas secretion to Duodenum
Function: Cleaves bonds, from C-Terminal
Product: AAs, tripeptide, dipeptide
Pro-carboxypeptidase
Activating agent: trypsin
Active enzyme: carboxypeptidase (A, B)
Location: pancreas secretion to Duodenum
Function: cleaves bonds from C-Terminal
Product: AAs, dipeptide, tripeptide
Aminopeptidase
Location: intestinal mucosa
Function: Cleaves unspecific end AAs from N- terminal
Product: AAs
Dipeptidase
Location: intestinal mucosa
Function: cleaves dipeptides
Product: AAs
