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23 Cards in this Set

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Where does the urea cycle begin?
The urea cycle begins in the liver.
List the steps in the urea cycle.
NH4 + HCO3 to carbamoyl phosphate to citrulline to argininosuccinate to arginine to orthinine
What enzyme catalyzes the formation of carbamoyl phosphate from NH4 and HCO3?
Carbamoyl phosphate synthestase I
? and ? form citrulline and what catalyzes the reaction?
carbamoyl phosphate and ornithine; ornithine transcarbamoylase.
How does aspartate enter the urea cycle?
From the transamination of oxaloacetate in the mitochonria and it is then transported to the cytosol.
Argininosuccinate is formed from ? and ? and its formation is catalyzed by what enzyme?
aspartate and citrulline; argininosuccinate synthetase
Argininosuccinate is cleaved to ? and ? catalyzed by ?.
arginine and fumarate; argininosuccinase (argininosuccinase lyase AL)
What is the only reversible step in the urea cycle?
The cleavage of argininosuccinate to arginine and fumarate.
What is the fate of the fumarate generated by the urea cycle?
It enters the mitochondria to join the pool of citric acid cycle intermediates.
Arginine is cleaved to yield ? and ?
urea and ornithine
List the enzymes involved in the urea cycle.
carbamoyl phosphate synthetase I, ornithine transcarbamoylase, argininosuccinate synthetase, argininosuccinase (lyase), arginase
How are the citric acid cycle and the urea cycle linked?
Aspartate is generated by the CA cycle and shuttled to the cytosol for the urea cycle. Fumarate generated by the urea cycle is converted to malate and enters the CA cycle.
How is the activity of the urea cycle regulated?
Via regulation of the synthesis of the urea cycle enzymes + carbamoyl phosphate synthetase I and by allosteric regulation of CPSI via N-acetylglutamate.
What is arginine's effect on the urea cycle?
Arginine is an activator of N-acetylglutamate synthase, and thus an activator of the urea cycle.
Deficiencies in which enzyme do not result in symptomatic hyperammonemia as severe or often as other UCDs?
Arginase.
Clinical symptoms are most severe when the UCD is at the level of which enzyme?
CPS I
What are the common elements of treatment of UCDs?
Reduction of protein in the diet, removal of excess ammonia and replacement of intermediates missing from the urea cycle.
The administration of ? reduces ammonia through its action of ?.
Levulose; acidifying the colon
How can antibiotics be used in the treatment of UCDs?
Antibiotics can be administered to kill intestinal ammonia-producing bacteria.
What two medications can be administered to bind glycine and glutamine?
Sodium benzoate and sodium phenylbutyrate
What is the most common type of UCD?
OTC
Which UCD is the most rare?
Arginase
Which amino acids are not produced by the human body and therefore are essential?
PVT. TIM HALL
Phe
Val
Thre
Trp
Ile
Met
His
Arg
Leu
Lys