Lecture 19 - Digestion and Absorption of Protein Flashcards
_________ are enzymes that need to be cleaved at one or more sites in order to become active/functioning.
A. Proenzymes
B. Endopeptidases
C. Exopeptidases
A
__________ cleave proteins by hydrolyzing peptide bonds within the polypeptide chain.
A. Proenzymes
B. Endopeptidases
C. Exopeptidases
B
_________ cleave AA from either N or C terminal ends of peptides or proteins.
C
Pepsin is produced by what organ?
stomach
Trypsin and chymotrypsin are produced by what organ?
pancreas
Peptidases are produced by what organ?
small intestine
What are two non-enzymatic components of gastric juice?
- Gastin
2. HCl
Gastrin acts on the _______ cells to secrete HCl.
parietal
Gastrin acts on the ________ cells to secrete pepsinogen.
chief
HCl decreases pH to denature protein and provide a proper environment for _______.
pepsin
Secretin and CCK are secreted in response to what?
Chyme moving through duodenum
Secretin stimulates the release of _________.
pancreatic juice
CCK stimulates the release of ___________ into the lumen of the small intestine.
pancreatic zymogens
Enteropeptidase catalyzes what reaction?
Conversion of trypsinogen to trypsin
What are the (2) products of protein digestion within the lumen of the small intestine?
35% neutral and basic AA
65% oligopeptides
In the pathway of AA transport from the lumen of the SI to the portal blood, AA first go through the brush border where they are further hydrolyzed by _____.
oligopeptidases
Dipeptides and tripeptides are taken up by AA transporters using a _________ and then hydrolyzed by peptidases in intestinal cells.
proton gradient
Transport proteins (most are Na+ dependent) take AA through the _______ membrane, from the intestinal cell to the portal blood.
basolateral
Enteropeptidases are found where?
Brush border of intestinal cells
If an AA can’t be absorbed in the intestine, it also can’t be absorbed in the ________ and is excreted.
kidney
Long-term use of proton pump inhibitors can result in _________________.
vitamin B12 deficiency
What are two enzymes that require B12 as a cofactor?
- Methylmalonyl-CoA mutase (synthesizes succinyl-CoA in TCA cycle)
- Methionine synthase
Succinyl-CoA is required for _________ synthesis, so a B12 deficiency results in megaloblastic anemia.
heme
