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What is the only macronutrient with a significant source of nitrogen?
protein
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What is the major form of nitrogen loss?
unrine as urea
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When is there a positive nitrogen balance?
growing children, pregnant women, body builders
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When is there a negative nitrogen balance?
- protein deficiency (deficiency in one amino acid, starvation)
- severe diseases (infections, wasting diseased, burns)
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What three ways are the amino acid pool replenished?
- digestion and hydrolysis of dietary protein
- hydrolysis of body protein
- de novo synthesis of non-essential amino acids
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What three ways are is the amino acid pool depleted?
- body protein synthesis (protein turnover)
- gluconeogenesis
- synthesis of nitrogen containing compounds
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When are body proteins degraded? (3 times)
- they are damaged
- they are no longer needed
- amino acids are needed for energy metabolism of gluconeogenesis
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What are the three proteases involved in protein turnover/degredation?
- Serine protease (digestion and blood clotting)
- Ubiquitin-Proteasom system (ubiquitin-tagged proteins)
- Cathepsins (cysteine protease, lysosomal enzymes)
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How are amino acids transported into cells of the intestine?
Secondary active Na+ dependent transport (sodium dependent transport)
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What is celiac sprue?
immune mediated inflamation and damage of the mucosa in the small intestine (in response to gluten peptides; gluten intolerant)
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What is Hartnup disease?
defective transporter for neutral amino acids (typtophan) in apical membanes of intestine and kidney (only clinical manifestation is deficiency of tryptophan, bacterial formation of unabsorbed tryptophan in intestine, CNS intoxication, foul smelling stools)
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What is cystinuria?
- deficiency of transporter for dibasic amino acids (cystine, ornithine, arginine lysine=COAL) in apical membrane of small intestine and proximal tubule
- urinary exretion of cytosune and dibasic amino acids in urine
- can form bladder stones
- prevent by drinking lots of fluids
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What two mechanisms degrade body proteins to replenish amino acids?
- ubiquitin-proteasom system (degrades short-lived protein, highly ATP consuming)
- autophagy-lysosome pathway (degrades long-lived proteins, less energy consuming)
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What inhibits ubiquitin proteasome proteolysis?
What activates it?
- Inhibits: insulin
- Activates: starvation, immobilization, denervation, severe catabolic states
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What inhibits autophagy-lysosome proteolysis?
What activates it?
- Inhibits: insulin
- Activates: nutrient depletion, glucagon, stress hormones
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What is a hypercatabolic state?
- elevated levels of cortisol and epinephrine, accelerated protein degradation, muscle wasting
- amino acids mobilized from muscle for gluconeogenesis, acute phase proteins in the liver, provision of glutamine as a fuel for lymphocytes, hepatocytes, intestinal mucosal cells
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What are complementary proteins?
Foods when eaten together or in the same day give you a balanced supply of essential amino acids
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Why do non-exercising, non-growing, healthy adults need to consume protein?
- obligatory nitrogen loss; nitrogen is contiually lost through amino acid catabolism, growing hair and nails, sloughing cells
- necessary for maintenance of nitrogen balance
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