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33 Cards in this Set

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What is trypsinogen? How is it activated?
Proenzyme excreted from pancreas into small intestine and activated to Trypsin (digestive protease) by proteolytic cleavage by enteropeptidase from GI epith cells. Also Trypsin can then form more active rest of proenzymes
What is pepsinogen? How is it activated?
Stomach proenzyme activated to pepsin (protease) by low pH (H+).
What activates the following: chymotrypsinogen, proelastase, procarboxypeptidases?
Trypsin
How are peptides taken up from intestinal lumen & circulation?

How are they released into circulation
Via Na co-transport. Dipeptides through H co-transport.

released via facilitated transport
What is Hartnup disease (autosomal recessive)?
How is it treated?
Def. in uptake of neutral/hydrophobic AAs (including Trp). If pt is also def. in B3 (niacin deficiency) = decreased NAD+ production = photosens., tremors, ataxia, nystagmus (pellagra-like) symptoms

Tx: Niacin rich diet, high protein diet.
What AAs are elevated in the urine of patients with cystinuria.
Cystine, Ornithine, Arginine, Lysine. ("Can Only ARGue LYS" or COAL)
What is the cause and tx of cystinuria?
Def. uptake of COAL at the brush border leading to cystine stones (in kidney, ureter, & bladder) and hyperaminoaciduria.
Tx: High fluid intake and meds that elevate urine pH.
What is lysinuric protein intolerance (autosomal recessive)?
Tx?
Defect in basal transport of basic AAs. (OAL). Patients get hyperaminoaciduria of basic AAs, low plasma basic AAs (dec urea) & secondary hyperammonemia after meals (n/v).

Tx with arginine and nitrogen scavengers to reduce blood ammonia. Also protein restr. high cal diet
What are matrix metalloproteinases and what do they require?

What are cathepsins?
main proteastes involved in extracellular matrix turnover, require zinc

Major lysosomal proteases.
What is ubiquitin?
A small protein that "marks" other intracellular proteins for degradation by proteasomes.
What does a proteasome need to function?
CAP proteins (ATPases) to feed the protein into protease for degradation & ATP to unfold protein & thread into proteasome core
Why is Bortezomib (Velcade) effective in tx MM and certain lymphomas?
It is a protease inhibitor. It is thought to stop the degradation of pro-apoptotic factors leading to cancer cell death.
What is the result of the chromosomal deletion that occurs in Angelman syndrome?
Codes for E3 subunit of ubiquitin ligase.

symptoms: delayed development/mental retardation, speech impairment, happy demeanor, frequent laughing, movement & balance disorders, seizures
What is Von Hippel-Landau syndrome?
Def. in E3 ubiquitin subunit (VHL) prevents destruction of hypoxia inducible factor (factor that promotes angiogenesis).

symptoms: Inc. incidence of tumors (angiomatosis)
What is the fate of the vast majority of AAs in the fed state?
*stored dynamically in functional proteins (80% skeletal muscle)

AAs are shuttled to liver and broken down. C core is used in the synthesis of glycogen and TGs. N is excreted in the urine as urea or NH4.
How are AAs utilized during fasting?
Skeletal muscle (esp. myosin) is broken down into AAs and sent to the liver to produce glucose through gluconeogenesis.
What is the major glucogenic AA?
Alanine
Which organs provide what AAs to the AA pool?
Kidney and intestine - alanine.
Sk. muscle - All, but mainly alanine and glutamine. Brain - glutamine.


*ala & glu most important AAs in blood AA pool
How is glutamine used as an energy source in fast dividing cells?
Glutamine is converted to glutamate and then to alpha-ketoglutarate (by transaminases) and fed into the TCA.
How does usage of the AA pool shift during metabolic acidosis?
Most glutamine is shuttled to kidney to produce NH4 (ammonia), facilitating excretion of H+ ions.
-process coupled w/ bicarbonate release to circulation
How does usage of the AA pool shift during sepsis?
AAs are preferentially used by the liver to produce proteins used in acute phase reactions and to immune cells for energy (glutamine is especially used here).
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List main sources of AAs
de novo synthesis
digestion of dietary proteins
intracellular protein digestion
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List main utilization of AAs
protein synthesis
degradation/energy source
synthesis of other biomolecules
cell signaling
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Explain positive/negative nitrogen balance & when occur
positive: N intake > N excretion
-during growth/pregnancy or recovery

negative: N intake < N excretion
-during illness or malnutrition
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List proteases that participate in digestion of dietary proteins
Stomach: pepsinogen, HCl
Pancreas: HCO3-, trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidases
Duodenum: aminopeptidases, dipeptidases, enteropeptidase
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explain proteolytic cascade that acts in duodeunum
Enteropeptiidase activates proenzyme typsinogen from pancreas to trypsin, then trypsin activates rest of the proenzymes (chymotrypsinogen, proelastase, procarboxypeptidases) into chymotrypsin, elastase, & carboxypeptidase
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How does dietary AA absorption relate to reabsorption of AA in kidneys?
1. AA absorbed through brush border of intestinal lumen (Na+ cotransport)
2. AA are released into circulation via portal vein (facilitated transport)
3. AA reabsorbed by proximal tubules of kidney (Na+ cotransport)
If an AA cannot be absorbed by the intestine it cannot be reabsorbed from the glomerular filtrate (kidney) either, where will it go?
AA will accumulate in urine

**thus AA absorption diseases can be detected by elevated AAs in urine
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explain lysosomal protein degradation

What type of proteins are degraded this way?
Protease digestion & removal


-endocytosed proteins, phagocytosed particles, & autophagy (intracellular organelles)
What do protein digestion disorders that are caused by loss of digestive proteases lead to?

How are they treated?

what are 2 examples?
lead to malabsorption which leads to malnutrition, low serum protein levels, using albumin as a diagnostic tool, poor growth in children

treat w/ pancreatic enzyme supplement

EX; cystic fibrosis, chronica pancreatitis (alcoholism)
How do cystic fibrosis & chronic pancreatitis result in a loss of digestive proteases?
cycstic fibrosis: Cl- channel deficiency, leads to dried secretions blocking pancreatic duct

chronic pancreatitis: damage to pancreas, leads to loss of enzyme secreting pancreatic cells
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explain ubiquitin protein degradation
-protein "marked" w/ ubiquitin for degradation, machinery present in cytosol & nucleus will then degrade

-misfolded/damaged intracellular proteins, turnover proteins (myosin & transcription factors)
How are AAs used in the brain (normally)?
1. branched chain AAs (BCAAs) are transported through blood brain barrier by transporters
2. in astroglial cells, amino group of BCAAs undergoes transamination to make glutamate, which is converted to glutamine
3. glutamine is transported to neurons & converted back to glutamate & GABA