Protein I Flashcards
Where does protein digestion begin and what occurs?
Begins in the stomach where HCl reduces the pH of the stomach
What does acidification in stomach do for protein digestion?
Low pH favors protein denaturation and activates pepsinogen to pepsin
What is pepsin?
Gastric protease
Endopeptidase - cleaves internal peptide bonds
Secreted as inactive zymogen known as pepsinogen
Stable and active at low pH
Describe pepsin activation
Pepsinogen inactive because active site blocked by conformation structure
Low pH alters pepsinogen conformation
Small peptide is removed via hydrolysis and the active site is unblocked
What reaction can pepsin catalyze?
Autocatalytic reaction where pepsinogen generates active pepsin from itself
What is the function of pepsin?
Cuts proteins into large peptide fragments and contributes to formation of partially digested food (chyme)
Cleaves bonds formed by amino groups of aromatic amino acids and leucine
How does protein digestion continue in the intestinal lumen?
Chyme enters the intestines and stimulates the cells of intestinal mucosa to release the hormones, secretin and cholecystokinin into the blood
What is the function of secretin?
Stimulates the pancreas to release bicarbonate (HCO3) rich fluid which neutralizes the acidic chyme
What is the function of cholecystokinin?
Stimulates release of bile from the gallbladder and release of digestive enzymes from pancreas into the lumen of the small intestine
What are the pancreatic digestive enzymes?
Trypsin
Chymotrypsin
Elastase
Carboxypeptidase A and B
All secreted as inactive zymogens and their activation starts with enteropeptidase
What is enteropeptidase?
Membrane anchored protease, found on surface of mucosal villae.
Converts trypsinogen into active trypsin
What occurs when trypsin is activated?
Cascade of enzyme activation is initiated.
Trypsin autoactivates itself and then activates the rest of the zymogens and liberase chymotrypsin, elastase, and carboxypeptidase A and B
Pancreatic proteases and peptidases then generate a mixture of free amino acids and short peptides
Acute Pancreatitis
Causes - Alcohol, gallstones, infections. Premature activation of trypsin within the pancreas
Symptoms - Abdominal pain, nausea, vomiting, and pancreatic necrosis (advanced)
How are amino acids absorbed?
In the intestinal lumen, free amino acids and small peptides are present and must be transported across intestinal epithelial membrane by carrier transporters that require energy input provided by:
Proton gradient
Sodium electrochemical gradient
What does the proton dependent transporter transport on apical side on intestinal lumen?
Di and Tri peptides -> di and tri peptidases produce free amino acids from the peptides
