Protein Digestion Flashcards
(23 cards)
What two important products are found in the stomach that participate in protein breakdown?
Acid denatures proteins, pepsin produces peptide segments.
How is pepsinogen activated to pepsin?
Pro-peptide fragment is cleaved at acidic pH to activate the enzyme.
Which cells make pepsinogen?
Chief cells and pancreatic acinar cells.
What does enteropeptidase do to trypsinogen?
Cleaves it to trypsin. Trypsin can then cleave trypsinogen (pos. feedback)
How does the body deal with trypsinogen that is accidentally activated in the pancreas?
Trypsin inhibitor.
Name two ways in which trypsin inhibitor can be insufficient, resulting in pancreatitis.
- Duct blockage - inhibitor is overwhelmed.
2. Mutant trypsin - inhibitor cannot bind to mutated protein.
Are AAs actively transported into the intestinal cells?
Yes, with a Na+ linked transporter similar to glucose.
What is cystinuria?
Defective cysteine transporter. Cannot resport cysteine from presumptive urine. Cysteine has low solubility and this results in stones in the PCT.
What other AA is transported using the cysteine transporter?
Lysine
What is Hartnup disease?
Defective tryptophan transporter. Results in abnormal excretion into urine and abnormal intestinal absorption. Tryptophan is a precursor to niacin, niacin deficiency –> NAD+ deficiency –> Pellagra (D3 symptoms)
What are three non-dietary AA sources?
- Lysosomal system
- Digestive enzyme turnover
- Ubiquitin/proteasome pathway (major)
How long are the AA fragments that proteasomes poop out?
7-10 AAs long
What are the names of the enzymes that add ubiquitin to proteins?
E1, E2, E3
What enzyme recycles ubiquitin?
Deubiquitinase enzyme
What are the two choices for proteins that are pooped out of the proteasome?
Go to MHC I or get incorporated into new AAs.
What ubiquitination signal means that the protein will be longest-lived?
Methionine on N terminus
How does HPV E6 work?
E6 binds to p53, which attracts E6-AP, which adds ubiquitin to p53 —> degradation of p53
What is the Parkin mutation involved with?
Decreased ability to poly-ubiquitinate proteins. Proteins build up (Lewy bodies) –> neurodegeneration.
Aside from Parkin mutation, what is another enzyme linked to Parkinson’s disease involved in UPP?
Deubiquitinase, which recycles ubiquitin, is defective, so ubiquitinated proteins build up.
What are the essential AAs?
Phenylalinine, valine, threonine, tryptophan, isoleucine, methionine, histidine, arginine, leucine, lysine
(PVT TIM HALL)
What is kwashiorkor?
Insufficient protein in diet. First-child-after-the-second-child-is-born-and-is-now-not-getting-enough-protein-from-mother’s-milk disease.
Name four enzymes made in the pancreas.
- Trypsinogen
- Chymotrypsinogen
- Proelastase
- Procarbodypeptidases
What is the difference between carboxypeptidases and aminopeptidases?
Carboxypeptidases cleave at carboxy end, aminopeptidases cleave at N end.
