L1 : amino acid metabolism Flashcards
what is kwashiorkor?
a severe form of protein malnutrition
what is kwashiorkor caused by?
insufficient protein consumption
what happens as a result of insufficient protein consumption?
osmotic imbalance in the GI system which leads to gut swelling
what is gut swelling also known as?
edema or water retention
gut swelling decreases the body’s ability to produce:
- new intestinal epithelial cells
2. digestive enzymes
what is the aim of digesting dietary proteins?
hydrolyzing proteins into di- and tri- peptides and free amino acids
where does the digestion of proteins begin?
the stomach
where does the digestion of proteins end?
the small intestine
where are proteolytic enzymes produced?
- stomach
- small intestine
- pancreas
what is secreted by parietal cells?
HCl
what does HCl do?
denatures proteins and kills some bacteria because its too dilute to hydrolyze the proteins
what is secreted by chief cells?
pepsin; as an inactive zymogen (pepsinogen)
what is pepsin?
an endopeptidase
how is pepsinogen activated to pepsin?
- low pH of HCl
2. autocatalytic activation by other pepsin molecules
what is the type of mechanism in which autocatalytic activation runs?
positive feedback mechanism
what is the function of pepsin?
release peptides and a few amino acids
what is the release of zymogens in the pancreas mediated by?
two hormones; cholecystokinin and secretin
how are zymogens activated in the pancreas?
a duodenal enteropeptidase converts trypsinogen to trypsin
how are all pancreatic zymogens activated?
by trypsin
what is the specificity of trypsin?
cleaving only after arginine and lysine
how is digestion done in the small intestine?
by aminopeptidases
what is the classification of aminopeptidases?
exopeptidase
where are aminopeptidases found?
the luminal surface of the intestine
what do aminopeptidases do?
repeatedly cleaves the N-terminal residue from oligopeptides
when oligopeptides are cleaved what do they form?
smaller peptides and free amino acids
how are free amino acids absorbed?
intestinal enterocytes by Na+ linked secondary transport system
how are the di and tri peptides absorbed?
H+ linked transport system
how does the Na+ leave the cell?
Na/K pump
how are free amino acids RELEASED?
facilitated transporters; to be metabolized by the liver
how many transporters have overlapping specificity?
at least 7
what do the small intestine and proximal tubule of the kidney share?
common transport systems for AA uptake
which amino acid do the small intestine and proximal tubule of the kidney have an affinity to, and what disease may it lead to?
cystine; cystinuria
what is cystinuria?
its an inborn error of metabolism characterized by a genetic defect in the transport system which leads to an accumulation in the amino acids
what is the role of HCl in digestion?
denatures proteins
what initiates protein digestion in the stomach?
pepsin
which hormone stimulates the release of pancreatic zymogens?
cholecystokinin
which cells produce pepsin?
chief cells
where does the enzymatic digestion of proteins start?
stomach
what is a characteristic of pepsin?
autocatalytic
what is a characteristic of trypsin?
synthesized as a zymogen (trypsinogen)
what secretes gastric HCl?
parietal cells
how is pepsinogen activated?
positive feedback
