Protein Digestion Flashcards
Unlike carbs and lipids, digestion of proteins does not start until reaching the _____
stomach
note: digestion begins here due to acid conditions and pepsin
____ cells secrete HCl
parietal
K+, H+ exchanging ATPase is specific to ____ cells
parietal
In the stomach, Cl- is exchanged for what?
HCO3-
The pH of gastric juice is about ___
2
Pepsinogen and HCl secretion is stimulated by ___ and ____
histamine; gastrin
Pepsinogen is the zymogen of pepsin, secreted by ____ cells
chief
Pepsinogen is activated to pepsin by removal of ___ AA from the N-terminus, with auto-activation at a pH
46; 5
True or false? Pepsins are unstable and inactive at acidic pH
False; pepsins are stable and active at acidic pH
Pepsins are ____ peptidases that contain two _____ residues at the active site
carboxyl; aspartate
Pepsin begins proteolysis in the stomach. The product is mainly what?
large peptide fragments
The presence of AA, oligopeptides, and polypeptides in the duodenum stimulates secretion of what two things from intestinal endocrine cells?
- CCK
2. Secretin
CCK and Secretin stimulate secretion from ____
Pancreas (trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidases A and B, other digestive enzymes)
CCK stimulates intestinal mucosal epithelial cells to secrete ____
enteropeptidase
What does enteropeptidase do?
activates trypsinogen to trypsin (removal of a hexapeptide from N-terminus)
Trypsin further activates more _____
trypsinogen
____ is an endoprotease, and a carboxyl protease
pepsin
____, ____, and ____ are endoproteases, and serine proteases
trypsin, chymotrypsin, and elastase
Carboxypeptidases A and B are metalloproteases requiring ___
zinc
What are the products of intraluminal protein digestion?
Free AA (40%) Small peptides of 2-8 residues (60%)
What 3 protein digestive enzymes are found in the intestinal cell brush border?
- endopeptidases
- aminopeptidases
- dipeptidases
“EAD”
Brush border protein digestive enzymes produce what?
Free AA and di- and tri-peptides
The transport of di- and ti-peptides is usually dependent on ___ or ____
Na+ or H+ (active transport)
The intestinal epithelial cells contain intracellular dipeptidases and tripeptidases. These peptidases complete the breakdown to AAs which are transported to the ____ from the epithelial cells
blood
