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14 Cards in this Set
- Front
- Back
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Where does the C and N come from to produce urea?
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One N from aspartate, one from NH4, and C from CO2.
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In what 3 ways is N removed from AAs? What AAs are usually involved?
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Deamination (glutamate via dehydrogenase using NADH). Deamidation (glutamine and aspargine). Transaminases (transfer from alpha AA to glutamate).
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What coenzyme is required for transaminase?
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pyridoxal phosphate (need B6 - pyridoxine)
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What is the main way ammonia is detox. in the brain?
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Glutamate + NH4 via glutamine synthetase using ATP resulting in glutamine
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What are the 3 fxns of glutamate in the urea cycle?
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1. Picks up NH4 from other AAs via transaminase rxns 2. Can donate NH4 via glutamate dehydrogenase 3. Can transaminate OAA to aspartate which can then provide NH2
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Where does urea synthesis take place?
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Liver ONLY! (alanine and glutamine carry the N to the liver from other cells)
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Draw out the urea cycle
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See image.
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What is the rate limiting step in the urea cycle? How is it allosterically regulated?
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CPSI. N-Acetyl-glutamate is a positive regulator.
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When is N-acetyl-glutamate formed?
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High levels of arginine.
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What links the TCA to the urea cycle?
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Fumurate from urea cycle can be fed into TCA to yield energy. OAA can form aspartate through transamination and can be fed into urea cycle.
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What is the difference btw. urea synthesis during short term and long term fasting?
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Short term: Muscle breakdown. AAs transport to liver for gluconeo. and urea excretion thus increases. L/T: Ketone body synthesis is primary energy from FAs so urea excretion decreases.
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What causes Type I hyperammonemia?
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Def in CPS-1 or N-acetylglutamate synthase
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What causes Type II hyperammonemia?
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Def in ornithine transcarbamoylase. X-linked recessive.
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Will urine orotate be low/normal/high in Type II hyperammonemia? Why?
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HIGH. Shifts CP to alt. pathway when OTC is shut-down.
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